CLINICAL DENTAL PROSTHETIC'S Clinical Dental Prosthetics H. R. B. FENN F.D S. R.C S.(ENO.), D.D S.(PENN.) professor Emeritus of Dental Prosthetics, Unnersily of London and W 1 Director of Dental Prosthetics , Guy's Hospital Dental School Past Examiner in Dental Prosthetics , Dental Mechanics and the Properties of Dental Materials to the Royal College of Surgeons of England and to the Universities of Durham, Leeds, Liverpool, London, Manchester, Birmingham and Edinburgh Yt. ■?. UTSDELCyW F.D.S. R.C.S.(ENG.), If.D.D. R.C.S.(EDIN.J Professor of Dental Prosthetics, University of London Hedd °f the Prosthetic Department, King’s College Hospital Den'al School Honorary Consultant Dental Surgeon to King’s College Hospital Past Examiner in Dental Prosthetics and the Properties of Dental Materials to the Universities of Birmingham, Glasgow and Durham and m Dental Technology to the City and Guilds of London Institute Present Examiner to the Universities of London and Bristol and to the Royal College of Surgeons of England A. P. GIMSON L.D.S. R.C.S.(ENG.) Senior Lecturer in Dental Prosthetics, King’s College Hos fatal Dental School Examiner in Dental Technology, City and Guilds of London Institute STAPLES PRESS LONDON To All Past, Present and Future Dental Students AND TO All Technicians Without Whose Craftsmanship the Clinician’s Efforts Would Be Valueless CONTENTS Preface to the First Edition . . . . . . ix Preface to the Second Edition » . . . . . xi Introductory Historical Notes . . . . . . xiii i Introduction to Prosthetics . . . . i it Applied Anatomy . . . . . . . . 1 1 m History Taking and Examination of the Mouth 54 iv Simple Surgical Preparation of the Mouth . . 76 At Impression Taking 94 vi Recording the Position of Centric Occlusion . . 172 'vn The Selection of Teeth .. .. .. .. 224 vm Setting-up the Teeth in a Plane-line Articulator 235 ix Anatomical Articulation 264 x Phonetics . . . . . . . . ■ . • * 3 02 xi Trying in the Dentures . . . . . . • . 309 /xn Fitting the Finished Dentures . . . . . . 326 xm Check Records for Completed Dentures . . 336 xiv Complaints . . . . • . . . • * 3^5 xv Re-lining, Resilient Linings, Aids to Retention and Repairs 39 2 xvi Outline of Techniques Suitable for Overcoming Difficulties Encountered in Full Denture Prosthetics . . . . . • • - • • 4°^ xvii Appearance .. .. •• •• •• 4*7 vii CONTENTS Preface to the First Edition . . . . . . ix Prelace to the Second Edition . . . . . . xi Introductory Historical Notes . . . . . . xiii i Introduction to Prosthetics . . i ii Applied Anatomy . . . . . . . . 11 m History Taking and Examination of the Mouth 54 iv Simple Surgical Preparation of the Mouth . . 76 /v Impression Taking . . . . . . . . 94 vi Recording the Position of Centric Occlusion . . 172 / vii The Selection of Teeth .. .. .. .. 224 vm Setting-up the Teeth in a Plane-line Articulator 235 ix Anatomical Articulation 264 x Phonetics . . . . . . . . . - . . 302 xi Trying in the Dentures . . . . . . . . 309 /sn Fitting the Finished Dentures . . . . . . 326 xni Check Records for Completed Dentures . . 336 xiv Complaints . . . . . . . . . . 365 xv Re-lining, Resilient Linings, Aids to Retention and Repairs . . . . . . . . . . 392 xvi Outline of Techniques Suitable for Overcoming Difficulties Encountered in Full Denture Prosthetics . . . . . . . . . . 408 xvn Appearance .. .. .. .. .. 417 CONTENTS viii xvin Partial Dentures . . . . . . . . . . 454 xix Classification of Partial Dentures . . . . 469 xx The Component Parts of a Partial Denture . . 479 xxt Materials for Partial Denture Bases . . . . 536 xxn The Basic Principles of Partial Denture Design 544 xxra The Position of Partial Dentures in Relation to the Treatment of the Mouth as a Whole .. 618 xxrv Taking Impressions of the Partially Edentulous Mouth . . . . . . . . . . . . 634 xxv Recording of the Position of Occlusion in Partially Edentulous Cases 648 xxvi Immediate Dentures . . . . . . . . 662 xxvu Overlay or Onlay Dentures 689 xxvm The Cleft Palate from the Prosthetic Aspect . . 706 xxix Surgical Prostheses 767 xxx Implant Dentures 785 Bibliography .. .. .. .. 81 1 Index 819 PREFACE TO THE FIRST EDITION The justification for adding yet another textbook to the shelves of dental literature is to be found in the presentation of the subject matter and not in any novelty of technique. As teachers of undergraduate dental students we have become increasingly aware of the fact that the purely clinical aspect of dental prosthetics is still to quite a large extent over- shadowed by dental mechanics in current textbooks. Another shortcoming which we desired to remedy is that whilst there arc many books on full denture construction there arc few on partial dentures and none which give adequate information on both full and partial dentures in the same volume. An attempt has been made to explain the principles of denture construction, both full and partial, together with a detailed description of the clinical work involved and the reason for each particular operation. As this hook is intended primarily for undergraduate students whose time is necessarily limited, many excellent but more complicated techniques have purposely been omitted but it is hoped that this book is sufficiently comprehensive to guide the operator in the construction of dentures for all but the most unusual eases. The purely mechanical side of denture construction is not mentioned as it is already well catered for and the present trend in dental education is, rightly or wrongly, to increase the clinical knowledge and skill at the expense of the purely laboratory work. It will be obvious that we have freely consulted the available dental literature and whilst wc have neither quoted from it verbatim nor duplicated any illustrations wc have in a few instances followed it fairly closely and where this has occurred wc should like to express our appreciation to the Authors concerned. Wc would like to express our indebtedness to our many colleagues whose help and encouragement has made the production of this book possible. In particular wc should like ix PREFACE TO THE SECOND EDITION The first edition of this book, while covering the basic essentials of prosthetics, gave no information in the wider fields of the subject. Also since no textbook can remain permanently up to date, it was decided to revise certain sections and make some additions. The section on partial dentures has been largely re-written with many new illustrations. Several new chapters have been included dealing with perfecting the occlusion and articulation ; obturators; appearance and overlay and implant dentures, thus presenting in one volume all the essentials which a student should know before qualification and also making the book more useful to the practitioner. An experiment has been tried in this new edition with some trepidation - which is to drop the use of die term ‘bite’ taking, substituting where possible the word ‘record’ taking as being more in keeping with modern teaching: time will show whether this change is justified or not. The many suggestions and criticisms which have been received have all been carefully considered and we arc grateful for them, even though wc have not been able to incorporate them all. We should like to expicss our thanks particularly to Mr Wesley Johnson, who devoted a lot of his own time to preparing a detailed, constructive criticism of the first edition. This was of great help to us and many of his valuable amendments and suggestions have been incorporated in the second edition. We should also like to thank those who have so kindly and readily loaned us illustrations: Mr Adrian Haider, for fig. 1 8 1 (a), Mr Denis Glass for fig. 520, Professor Malcolm Gibson for fig. 514, and Mr Maurice Kettle for figs. 513, 5C5, 579, 580. Some of the additional photographs have been kindly taken by Mr A. Smith of the Photographic Department of King’s PREFACE College Hospital whilst Mr H. Bone, Mr T, Marshall, Mr F. Treacher, Mr G. Hough and Mr P. Nowell have produced many of the appliances and models used for illustration. Mr Roy Honeywood and Mr A. J. Bailey are responsible for the additional line illustrations and Mrs M. Harrison and Miss S. and Miss V. Uddelow have patiently typed and re-typed the new manuscript. To all of them we say thank you indeed for both your work and your forbearance. We should also like to record our appreciation of both the help and courtesy which we have received from the Production Department of Staples Press, especially from Mr Derek Morrison and Mr N. J. Cowan. Finally, but by no means least, we should like to record our gratitude to our wives for their help and forbearance during the long period of production of both the original and this second edition, without which the work could never have been completed. H. R. B. F. K. P. L. A. P. G. King’s College Hospital, Dental Department and School, London, S.E. 5. July 1961. INTRODUCTORY HISTORICAL NOTES Dental prostheses are undoubtedly among the earliest forms of dental treatment, the oldest existing denture being one of the lower six anterior teeth bound together with gold wire and attached by the same means to the adjacent natural teeth. It was made by the Etruscans in about 300 b.c. and shows a much higher degree of skill and craftsmanship than many specimens of a considerably later date. The early Japanese, in particular, constructed very crude dentures of wood with pebbles inserted to represent the teeth. Probably the earliest written reference to full dentures is in the preface to Blagravi’s ‘Mathematical Jewel’ (1585) in which the author mentions his nephew ‘who caused his teeth to be all drawn out and after had a sett of ivory teeth in agayne.’ Until the middle of the nineteenth century dentures were usually carved out of a solid block of ivory or bone, sometimes with natural teeth inserted in them and usually the anterior six uppers and lowers ( see fig. 181(a)). The useful life of these dentures was short as the materials were of course subject to caries and the fit could never have been more than approxi- mate. The carving was by trial and error though undoubtedly some marking medium was used in the mouth and Purman in 1684 mentions making a model of the mouth but from his description it is not clear whether his model was an impression or a cast. It was not until 1782 that impression taking is men- tioned, by William Rac who describes a technique for taking an impression in wax and pouring into it a cast of plaster of Paris. Although Philip Phaff of Prussia is usually credited with the introduction of models made of plaster of Paris. Pierre Fauchard may truly be regarded as the ‘Father of Dentistry'’ and his 'Chirurgien Dentiste' published in 1728 contains many detailed descriptions of various prostheses, including no fewer than five different types of obturators. xiii XIV PREFACE He obviously encountered some difficulty in keeping his dentures in place since he describes the use of springs for retention ‘where necessary’. It is interesting to note that George Washington’s dentures were retained by springs. The disadvantages of ivory and bone were obviously serious and metal bases of swaged gold or platinum were commonly used by the beginning of the nineteenth century and Chemant of Paris tried fused porcelain for both bases and teeth but his contemporaries, among whom was John Hunter, soon aban- doned it, having been unable to overcome the shrinkage when fusing. About 1774 Duchateau, an apothecary of Paris, and Dubois de Chemant, a dentist, made a whole denture from fused porcelain, but it was not until 1808 that Fouzi of Italy started making individual porcelain teeth and later (1837) Claudius Ash of London introduced fused porcelain tube teeth for the same purpose. The first thermoplastic denture base was probably used by Harrington of Portsmouth who in 1830 softened and moulded tortoise-shell but the introduction of vulcanized rubber by Goodyear in 1839 was really the beginning of modern dental prosthetics. \A quotation from Gutmann of Leipzig written in 1827 is interesting as showing the appreciation of the trifold functions of a denture. ‘In order to render the use of artificial teeth more widespread and more serviceable to the community, I refuse to accept a fee for installing them until patients have had one, or in certain circumstances even two, months in which to con- vince themselves of their suitability for ornament, for clear enunciation and for mastication.’ The technique of the casting of metal has a long history and the lost wax process was probably used by the Egyptians and the goldsmiths of Solomon to produce decorations for the temple. It was Taggart, however, in 1907 who first used this process for producing gold inlays and later it was used for dentures. A lot of trouble was experienced with the contraction of the metal and it is only in recent years that really accurate metal casting has been made possible. Chrome cobalt or an alloy of similar metals was discovered by Elwood Haynes in igo7 when experimenting to find a durable PREFACE XV alloy for the electrodes ot sparking plugs. In jgog R. W. Erdle and G. H. Prange of Austcnal Laboratories modified this alloy for casting dentures and patented it as Viiallium. It is inter- esting to note that this alloy played an important part in the development of the jet engine because its ability to maintain its physical properties at high temperatures was invaluable in this field. The acrylic resins arc of comparatively recent development and were first used for denture bases in 1935. The most recent developments in prosthetic dentistry arc probably the alginate materials introduced in about 1938 and the rubber base impression materials introduced in the ’50s. Chapter I INTRODUCTION TO PROSTHETICS Definition of Prosthetics A Prosthesis may be defined as an appliance which replaces lost or congenitally missing tissue. Some prostheses restore both the function and the appearance of the tissue they replace, others merely restore one of these factors. Prosthetics is the art and science of designing and fitting artificial substitutes to replace lost or missing tissue. Dental Prosthetics is a subdivision which deals with its application to the mouth. By definition dental prosthetics includes the replacement of any lost tissue and therefore embraces the filling of teeth and the fitting of artificial crowns. In actual practice, however, the term has come to mean the fitting of appliances such as artificial dentures, bridges, obturators, surgical prostheses and lip supports, and it is in this sense that the term will be used throughout this book. Why are Dentures Necessary? Before studying in detail the methods, techniques and theories employed in and relating to dental prosthetics, it is necessary to have clearly in mind the purpose which is being served. It is pertinent, therefore, to commence a book of this character by asking and answering the question - ‘Why do we make dentures?’ In order to answer this question the functions of the teeth must be understood. These are threefold: (1) To divide the food finely so that a large surface area is available for the action of the digestive juices. (2) To assist the tongue and lips to form some of the sounds of speech. (3) The teeth form an important feature of the face, and by supporting the lips and cheeks enable these structures to CLINICAL DENTAL PROSTHETICS perform their functions of manipulating the food and expressing emotion. The teeth are also mutually interdependent; premature loss of any tooth may cause a collapse of the dental arch, and movement of individual teeth, with loss of interprovimal contacts, thus giving rise to food-packing and gingival troubles. Function is necessary : (1) To minimize the risk of caries by preventing food stagnation. (2) To preserve the health of the soft tissues by the massaging action of the passage of food. (3) To prevent the over-eruption which may occur if a tooth is unopposed. Prior to the comparatively modem development of highly refined foods the loss of natural teeth often resulted in severe malnutrition but nowadays it is quite possible to live a perfectly healthy life with no teeth at all; in spite of this complete edentation is an unpleasant state for the following reasons: (1) It places limitations on the diet and all hard and fibrous foods require to be finely divided or else digestive troubles may result. (2) It produces a certain sibilance in the speech because those consonant stops requiring the presence of the teeth cannot be made efficiently. {3) It results in a prematurely aged appearance due to the loss of support and consequent falling in of the lips and cheeks, and the fact that the jaws can be overdosed produces a bunching up of the soft tissues around the mouth and close approximation of the chin and nose. f 4} It can produce loss of confidence and even psychological disturbances from the mutilated appearance. The results of edentation so far mentioned apply generally; there are other disadvantages applying individually. For instance: wind instrument players and singers are quitd unable to perform; clergymen cannot preach; actors and photographers’ models cannot follow their employment; and the pipe smoker loses Half the enjoyment of his pipe if he cannot hold it between his teeth. INTRODUCTION TO PROSTHETICS 3 To the majority of people, therefore, the loss of the teeth is a matter of great concern, and their replacement by artificial substitutes is vital to the continuance of normal life. What are the Differences between Natural Teeth and Artificial Dentures? Having seen that the replacement of the lost natural teeth by artificial substitutes is essential to the continuance of a normal life, the questions which logically follow must be answered. The essential difference between natural and artificial teeth is that the former are firmly rooted in the bone of the jaws, and in consequence they can incise, tear and finely grind food of any character because the lower teeth can move across the upper teeth with a powerful shearing action. Artificial dentures, on the other hand, merely rest on the gums and are held there by weak forces. In addition they are subjected to powerful dis- placing forces, so their efficiency ns a masticating apparatus is limited. This efficiency can vary within wide limits depending on the shape and size of the edentulous jaws, the type of gum tissue covering these jaws, the mental attitude of the patient to the dentures, his ability to learn to use them, and the skill of the operator. These factors are discussed at length in Chapter II. Aesthetically, artificial teeth can be indistinguishable from natural teeth, and in many cases they can enhance the appear- ance if the natural teeth were hypoplastic, grossly carious or unpleasantly irregular. The speech of artificial denture wearers should be normal once the tongue and lips have adapted them- selves to the dentures. Other functions such as singing, or musical instrument playing, can be made possible by modifying the dentures in various ways. The main limitations of artificial dentures therefore are that they lack stability, and the masticatory force which can be applied by them is limited by this fact , and also by the pressure which the gums will tolerate. In other respects they can closely rival natural teeth. ? What are the Displacing Forces Causing Instability? The most powerful displacing forces are the muscles surround- ing the oral cavity, and the tongue. One of the functions of the 4 CLINICAL DENTAL PROSTHETICS lips, cheeks and tongue is to receive and manipulate the food and pass it backwards and forwards between the teeth until it has been reduced to a sufficiently fine state for it to be formed into a bolus and swallowed. These movements are powerful, and unless the dentures are very firmly seated - which can be the case only if they have been properly designed and made by a careful and exact technique - and until the wearer has become skilful in manipulating them, they arc liable to be moved about with the food. In addition, every time the mouth is opened the muscles of the checks tense, and if the lower denture is over- extended at the edges it will be raised. Also during speech the tongue tends to tip, and, in bad cases, eject the lower denture unless it is properly designed. Other displacing forces requiring to be reduced by careful technique and design are: (i) The interference and locking of the cusps of the teeth as the lower move across the upper in chewing. Tins inter- ference tends to displace both dentures from their seating. (a) Viscous and sticky foods tend to unite the dentures and displace them. (3) Gravity will tend to unseat the upper denture. What are the Retaining Forces Available to Counteract Displacement? These can be divided into two classes: (a) Positive physical forces. (b) Acquired muscular control by the denture wearer. (a) The Physical Forces I. Adhesion and Cohesion Adhesion is defined as the apparent force of attraction existing between dissimilar bodies in close contact. This force acts most powerfully at right angles to the surface, and is pro- portional to the area of the surfaces in contact. Cohesion is the apparent force of attraction existing between similar bodies in close contact. An example of adhesion is afforded by two microscope slides with a scry thin film of water between them. The force required to separate the slides, provided it is applied at right INTRODUCTION TO PROSTHETICS 5 angles, wall be great, but if it is applied at a lesser angle the slides immediately commence to slip over one another and separate easily. The force of adhesion acts from one surface of the film of water to one glass slide and from the other surface of the film to the other glass slide. Within the film of water the force of cohesion unites the molecules, and the thinner the film the more powerful is this force. A denture base is made accurately to fit the mucous mem- brane on which it rests, and intervening between the two surfaces is saliva. The similarity to the microscope slide analogy is therefore obvious. Thus adhesion may or may not play an important part in retaining a denture in place, depend- ing on the shape of the mouth, its surface area, the closeness of apposition of the denture to the tissues, and the direction of the displacing forces. The accompanying diagrams should make this clear (see figs, i and 2). Adhesion is by far the greater of these two forces, as can easily be shown by placing a dry slide on a moist one and (hen forcibly separating them; both will be found to be wet, proving that the force holding the molecules of water together is less than that holding the water to the glass. A lower denture covers a very small surface area compared with an upper, and its adhesion is correspondingly less. The viscosity of the saliva is of importance in the phenomenon of cohesion. Saliva which is more viscous than normal, i.c. it contains a larger percentage of mucin, prevents the denture and tissues coming into sufficiently close contact because it increases the thickness of the saliva film and this reduces the cohesive force. 2. Atmospheric Pressure (Suction) The periphery of a denture should bed slightly into the soft tissues in the sulci, and except for the back edge of the upper denture it will be covered by the lips and cheeks, wrapped up as it were in the surrounding soft tissues. When an upper denture is inserted air is expelled from between it and the mucous membrane, and provided the fit of the periphery to the tissues is good no air can get in because this edge-fit provides an efficient seal (see fig. 3). This means INTRODUCTION TO PROSTHETICS 7 that the pressure acting on the fitting surface of the denture is less than that acting on the non-fitting surface (atmospheric pressure). The difference between these two pressures gives a positive force holding the denture in place. Furthermore, if the denture tends to move out of contact with the tissues, provided the seal at the periphery is not broken, the pressure under the denture will tend to fall still further and the atmospheric force will increase. 3. Undercut Area It is often possible to insert a denture in one direction into what, from another direction, is an undercut area and thus obtain a purely mechanical retention (see fig. 4). (b) Acquired Muscular Control Dentures are always foreign bodies in the mouth and when fitted for the first time most muscular actions tend to expel them. Gradually, however, the wearer learns to differentiate between the food and the dentures and, at first consciously but later subconsciously, to control and stabilize them with the tongue and the cheeks. The tongue, by resting on top of the lower denture and pressing it downwards and forwards, can conti ol its tendency to rise, and also counterbalance to a large degree unstabilizing masticatory forces. The tongue can also be unconsciously trained to prevent the back edge of the upper denture dropping while the front teeth are incising. (a) The large flat surface of a microscope slide provides excellent adhesion uhen resisting vertical separation. (4) A sliding force allows easy separation. (a) A flat palate will provide good surface adhesion, jfc) A V-shaped palate allows sliding anti therefore retention by adhesion w reduced. (c) A low er denture provides a s ery small surface for eflrc- tite adhesion INTRODUCTION TO PROSTHETICS 7 that the pressure acting on the fitting surface of the denture is less than that acting on the non-fitting surface (atmospheric pressure). The difference between these two pressures gives a positive force holding the denture in place. Furthermore, if the denture tends to move out of contact with the tissues, provided the seal at the periphery is not broken, the pressure under the denture will tend to fall still further and the atmospheric force will increase. 3. Undercut Area It is often possible to insert a denture in one direction into what, from another direction, is an undercut area and thus obtain a purely mechanical retention {see fig. 4). (b) Acquired Muscular Control Dentures are always foreign bodies in the mouth and when fitted for the first time most muscular actions tend to expel them. Gradually, however, the wearer learns to differentiate between the food and the dentures and, at first consciously but later subconsciously, to control and stabilize them with the tongue and the cheeks. The tongue, by resting on top of the lower denture and pressing it downwards and forwards, can conti ol its tendency to rise, and also counterbalance to a large degree unstabilizing masticatory forces. The tongue can also be unconsciously trained to prevent the back edge of the upper denture dropping while the front teeth are incising. 8 CLINICAL DENTAL PROSTHETICS The muscular cheeks can be trained, again unconsciously, to press downwards on the buccal flanges of the loner denture, whilst still earning out their function of placing food between the teeth. If full use is to be made of muscular control of dentures, their design must follow certain lines which are fully explained in the following chapters. Fig. 4 (ai If the denture is inserted directly upwards it will not go into place. \i) If the denture ts inserted from the right side, the flange of the denture will go into place and the opposite side may be rotated upwards. The right side of the denture will be retained by the undercut, once in place. INTRODUCTION TO PROSTHETICS 9 Why are There So Many Techniques? The novice in prosthetics may become bewildered by the plethora of techniques which exist for achieving the same result. For example, there are at least a dozen techniques for taking an impression of the mouth, and almost as many for determining the relationship which the jaws bear to one another. There are many different types of articulator and an equal number of posterior tooth forms. This list could be greatly extended, but the examples given serve to draw attention to the fact. Furthermore, individual operators tend to select and practise a very limited number of techniques, and regard the others with indifference or even open hostility. The explanation for this state of affairs is briefly as follows: Prosthetics is not an exact science; it is very’ largely an art, and although certain aspects of it do follow rigid laws the major part of the subject follows lines laid down by practi- tioners who have developed their craft by their own clinical experience and research. Such practitioners have given rise to what may be termed ‘schools of thought’, and pupils who have learned from them have perpetuated their methods. In addition, mouth conditions of individuals vary' within wide limits; some presenting jaw formations which make the fitting and subsequent function of dentures a comparatively simple matter, while in others difficulties of retention and occlusal relationship and other factors require that special techniques be used in order to make use of every small advan- tage which is presented, if ihe dentures are to have any chance of success. In an attempt to achieve this, many techniques with the same aim have been evolved, and no one of them has been of such outstanding merit as to displace the others entirely. Closely bound up with this is the fact that all these techniques require the development of a high degree of skill in the pros- thetist who practises them, and if one technique is producing good results in the hands of one practitioner he is likely to advocate its use and continue to practise it to the exclusion of others. io CLINICAL DENTAL PROSTHETICS Finally, in certain aspects of prosthetics, agreement has not been reached on how and why certain phenomena and func- tions occur and, as in other branches of science, conflicting theories exist, each with its adherents. For example, in the field of articulation of the teeth, G\si and Hanau have related the movements of the mandible to the guidance it receives from both the temporo-mandibulnr joints and the slope of the tooth surfaces in contact during movement. Monson and Boyle, on the other hand, has e evoked the theory that the movements of the mandible follow the segment of a sphere, the centre of which is located near the crista galli. Articulators and posterior teeth have been designed to enable dentures to be made conforming to the principles of these theories, and as both apparently produce satisfactory results both have their adherents. Speed and economy ha\e also had a powerful effect on the development of techniques because the cost of artificial dentures bears a very definite relationship to the time spent on their construction, and simple quick methods have a wide appeal in spite of the fact that they frequently produce dentures which arc very' inferior in comparison with those which could be made by more elaborate and time-consuming techniques. The only safe guide to be followed by the student of pros- thetics is to Icam to anticipate the difficulties which a given case will present, study any technique which is designed to overcome the difficulties, and select for his practice the one which appeals to him most and produces in his hands the best result. Chapter II APPLIED ANATOMY This section indicates how a knowledge of the structure and function of the tissues in the immediate vicinity of the dentures can be used to determine their logical design and provides reasons for, and answers to, some of the difficulties which are encountered in full denture prosthesis. The mouth only represents a true cavity when opened to receive food or during the formation of certain sounds of speech; at other times it is filled almost completely by the tongue and edentulous alveolar ridges. Fig. 5 shows the appearance of an open edentulous mouth with the tongue depressed. 12 CLINICAL DENTAL PROSTHETICS The Mucous Membrane Tissue Compression The varying thickness of the mucous membrane and sulv. mucous tissue covering the hones forming the palate and alveolar ridges results in the forces which arc applied to the denture during mastication being transmitted unevenly to these supporting structures. In addition to this varying thickness, there is a variation in the closeness of packing of the fibrous elements of the corium. Soft tissue is compressed when a force is applied to it due to the fact that some of the fluids {blood and lymph) which it contains, arc temporarily driven out of it. The amount oflluid which a soft tissue contains is dependent both on its thickness and the density of its elements. Reference to figs. G and 7 will show that the thinnest and densest layer of mucous mcmbrauc covers the mid-line of the hard palate; that the next thinnest is over the alveolar ridges and that the thickest layer covers the blood vessels and nerves. It will he apparent, therefore, that if a denture base accurately fits the mucous membrane at rest when the denture is driven upwards during mastication the first resistance offered to it will he by the thin tissues of the centre or the palate. Some of the remaining force will then he dissipated in flexing the denture base on either side of the mid-line until it has sufficiently compressed the slightly thicker to sues over- laving the alveolar ridges which then transmit the forces to "lie underlying bone. The tissues between the mid-line of the pal.. c and the alveolar ridges being both thick and vascular will piv^ably never be compressed sufficiently to transmit any appreciate force to the hone. Such t st;ac of affairs is likely to result in two things: V- The ‘■■‘Avre-s vr» live w&vWvwc *>£ dvt yvxUtc will become infix men. {2) The com tar. fl cx i t ig of the denture base will cause its fracture from f-^que. Means of nvnwm«\ t he-c results of uneven soft tissue distribution arc dealt viddv, t } JC chapter on impressions. APPLIED ANATOMY Fic. 6. - This coronal diagram through the tst molar region illustrates the varying tluckness of the mucous membrane co\ enng the oral structures. 12 CLINICAL DENTAL PROSTHETICS The Mucous Membrane Tissue Compression The varying thickness of the mucous membrane and sub- mucous tissue covering the bones forming the palate and alveolar ridges results in the forces which are applied to the denture during mastication being transmitted unevenly to these supporting structures. In addition to this varying thickness, there is a variation in the closeness of packing of the fibrous elements of the corium. Soft tissue is compressed when a force is applied to it due to the fact that some of the fluids (blood and lymph) which it contains, are temporarily driven out of it. The amount of fluid which a soft tissue contains is dependent both on its thickness and the density of its elements. Reference to figs. 6 and 7 will show that the thinnest and densest layer of mucous membrane covers the mid-line of the hard palate; that the next thinnest is over the alveolar ridges and that the thickest layer covers the blood vessels and nerves. It will be apparent, therefore, that if a denture base accurately fits the mucous membrane at rest when the denture is driven upwards during mastication the first resistance offered to it will be by the thin tissues of the centre of the palate. Some of the remaining force wall then be dissipated in flexing the denture base on either side of the mid-line until it has sufficiently compressed the slightly thicker tissues over- laying the alveolar ridges which then transmit the forces to "he underlying bone. The tissues between the mid-line of the pai**e and the alveolar ridges being both thick and vascular ill pUbably never be compressed sufficiently to transmit any appreciable force to the bone. Such a sti*te of affairs is likely to result in two things: (1) The tfic roid-Uwc of the palate will become infiamca. (2) The constat. fleeing G f the denture base will cause its fracture from ^Vuc. Means of overcoming these results of uneven soft tissue distribution are dealt w'ith t h e chapter on impressions. 12 CLINICAL DENTAL PROSTHETICS The Mucous Membrane Tissue Compression The varying thickness of the mucous membrane and sub- mucous tissue covering the bones forming the palate and alveolar ridges results in the forces which are applied to the denture during mastication being transmitted unevenly to these supporting structures. In addition to this varying thickness, there is a variation in the closeness of packing of the fibrous elements of the corium. Soft tissue is compressed when a force is applied to it due to the fact that some of the fluids (blood and lymph) which it contains, are temporarily driven out of it. The amount of fluid which a soft tissue contains is dependent both on its thickness and the density of its elements. Reference to figs. 6 and 7 will show that the thinnest and densest layer of mucous membrane covers the mid-line of the hard palate; that the next thinnest is over the alveolar ridges and that the thickest layer covers the blood vessels and nerves. It will be apparent, therefore, that if a denture base accurately fits the mucous membrane at rest when the denture is driven upwards during mastication the first resistance offered to it will be by the thin tissues of the centre of the palate. Some of the remaining force will then be dissipated in flexing the denture base on either side of the mid-line until it has sufficiently compressed the slightly thicker tissues over- laying the alveolar ridges which then transmit the forces to ♦he underlying bone. The tissues between the mid-line of the pau* c and the alveolar ridges being both thick and vascular "rill p»'bably never be compressed sufficiently to transmit any appreciate force to the bone. Such 1 state of affairs is likely to result in two things: (0 The in. the mid-line of the palate will become inflamea. (2) The consta*. fl^ng 0 f the denture base will cause its fracture from I«. :9 Types of Alveolar Ridges and Palale Formation and Their Significance Upper i Well developed but not abnormally thick ridges and a palate with a moderate vault {see fig. 14). This is a fav- ourable formation because: (a) The centre of the palate presents an almost fiat horizontal area and this will aid adhesion {see Chapter 1 ). 1 0) The roomy sulcus allows for the development of a good peripheral seal. (r) The well-developed ridges resist lateral and antero- posterior movement of the denture. Fig. 14 2 High V-shaped palate usually associated with thick bulky ridges ( see fig. 15). This is an unfavourable formation because the forces of adhesion and cohesion arc not at right angles to the surface when counteracting the normal displacing forces of gravity. F10. 15 3 Flat palate with small ridges and shallow sulci (see fig. iG). This is an unfavourable formation because: (a) The ill-developed ridges do not resist lateral and antero- posterior movement of the denture. {0) The sulci being shallow do not form a good peripheral seal. 20 CLINICAL DENTAL PROSTHETICS Fig. 16 4 Ridges exhibiting undercut areas (see fig. 17). These are unfavourable because frequently the flanges of the denture need to be trimmed in order to be able to insert it and this reduces the peripheral seal. He. 17 Lower 1 Broad and well-developed ridges (see fig. 18). This is a favourable formation because: (a) It provides a large area on which to rest the denture and prevents lateral and antero-posterior movement. (b) The surface presented for adhesion is as large as it can ever be in a lower jaw. (c) The lingual, labial and buccal sulci are satisfactory for developing a close peripheral seal. Fig. 18 2 Ridges exhibiting undercut areas (see fig. 19). Unfavour- able because: (a) If the denture is not eased away from the undercuts pain and soreness will result and, if it is eased, food will lodge under the denture. (b) The easing of the periphery will spoil the peripheral seal. APPLIED ANATOMY Fig. 19 3 Well developed but narrow or knife-like ridges ( see fig. 20). These are unfavourable because: (a) The pressure of the denture during mastication on the sharp ridge will cause pain. (i) There is no suitable surface presented for adhesion. Fio. so 4 Flat ridges (see fig. 21). These are unfavourable because no resistance is offered to anteroposterior or lateral movements. In addition, such ridges are frequently found to have absorbed to the level of the attach- ments of the mylohyoid, genioglossus and buccinator muscles and, if the denture base is kept sufficiently narrow not to encroach on these structures, its area is too small to be func- tional. If the area is increased by encroachment on the muscles they may move the denture when they contract. 0 ) I'm. ai (a) Illustrates a flat lower ridge in coronal section. \b) Illustrates the closeness of the attachments of the buccinator and m>Iohvoid muscles to a flat ridge. 22 CLINICAL DENTAL PROSTHETICS The Tuberosities Large tuberosities bounded by deep sulci offer very satisfactory resistance to the lateral movement of the denture. Tuberosities sometimes exhibit buccal undercut areas. If only one tuberosity is undercut this can sometimes be utilized to retain the denture on that side by slipping the dhtobucc.il flange up over the bulge first and then raising the other side of the denture (see fig. 22). Fic. 22 - If the denture is inserted from the right side, the flange of the denture will go into place and the opposites CLINICAL DENTAL PROSTHETICS APPLIED ANATOMY 31 In the mid-line the periphery is shaped to allow room for the labial fraenum (see fig. 29). Lingually, commencing at the crest of the ridge in the retromolar area, the periphery runs as follows: It runs downwards and slightly forwards, its direction being dictated by the most forward position assumed by the palato- glossus muscle ( see fig. 27). The depth to which it descends depends on the degree of absorption of the alveolar ridges and the laxity of the soft tissues. If there is little alveolar ridge the lingual pouch in this region is shallow. The periphery follows the curve of the palatoglossal arch and, as it runs forwards along the floor of the mouth its depth is limited by a slip of the superior constrictor muscle crossing to be inserted into the tongue. The tissues enveloping the periphery in this region rise to their highest position during swallowing and thus limit the depth of the denture which must not interfere with this move- ment. This position can be ascertained by placing a finger in the lingual pouch and asking the patient to swallow. 32 CLINICAL DENTAL PROSTHETICS From here it rises slightly to cross the narrow posterior edge of the mylohyoid muscle which sometimes is sufficiently well defined to produce a definite notch in the periphery in this region {see figs. 33 and 34). ! 10. 34. - Diagram through and molar region ol a "lower denture, illustrating ilie relation of tlie lingual Ilange to the ms loll) oid muscle. Ftc. 35. - Diagram through the 1st molar region of a tower denture, illustrating the relation of the lingual Ilange to the tongue, the sublingual gland and the mj lob) old muscle. Dotted line indicates the slope of the lingual flange. APPLIED ANATOMY 33 From this point forwards the periphery usually follows a gentle curve with the concavity looking downwards, dictated by the body of the sublingual gland which lies immediately underneath the mucous membrane forming the floor of the mouth {see figs. 33 and 35). When it reaches the first prcmolar region it descends again for a short distance and then rises to clear the lingual fraenum which sometimes presents a very broad attachment to the mandible {see fig. 36) . The polished lingual surface of the lower denture slopes downwards and inwards so as to present no area which over- hangs the tongue {see fig. 35). The Upper Denture The periphery of the upper denture commencing with the posterior edge is as follows: This edge, as already pointed out, should sink slightly into the non-movable tissues of the soft palate following a line from the hamular notch of one side to that of the other close to the foveae {see fig. 23). The posterior border then traverses the hamular notch and rises up into the sulcus on the buccal side of the tuberosity {see fig. 30). The height to which it rises is deter- mined by the attachment of the buccinator muscle in this region. From this point it commences to descend following the buccinator attachment, the lowest point of this descent being at the root of the zygoma {see fig. 30). The zygoma having been cleared, the periphery rises again but the height to which it is carried should not be excessive else the upper incisive muscle, when contracting, will displace the denture. Finally c 32 CLINICAL DENTAL PROSTHETICS From here it rises slightly to cross the narrow posterior edge of the mylohyoid muscle which sometimes is sufficiently well defined to produce a definite notch in the periphery' in this region (see figs. 33 and 34). Fig 34 - Diagram through 2nd molar region of a flower denture, illustrating the relation of the lingual flange to the rmlohjoid muscle Fig. 35. — Diagram through the ist molar region of a lower denture, illustrating the relation of the lingual flange to the tongue, the sublingual gland and the mylohyoid muscle. Dotted line indicates the slope of the lingual flange. APPLIED ANATOMY 33 From this point forwards the periphery usually follows a gentle curve with the concavity looking downwards, dictated by the body of the sublingual gland which lies immediately underneath the mucous membrane forming the floor of the mouth (see figs. 33 and 35). When it reaches the first premolar region it descends again for a short distance and then rises to clear the lingual fraenum which sometimes presents a very broad attachment to the mandible ( see fig. 36). The polished lingual surface of the lower denture slopes downwards and inwards so as to present no area which over- hangs the tongue ( see fig. 35). The Upper Denture The periphery of the upper denture commencing with the posterior edge is as follows: This edge, as already pointed out, should sink slightly into the non-movable tissues of the soft palate following a line from the hamular notch of one side to that of the other close to the foveae (see fig. 23). The posterior border then traverses the hamular notch and rises up into the sulcus on the buccal side of the tuberosity ( see fig. 30). The height to which it rises is deter- mined by the attachment of the buccinator muscle in this region. From firi? pome it commences to descend follcnving fhc buccinator attachment, the lowest point of this descent being at the root of the zygoma (see fig. 30). The zygoma having been cleared, the periphery' rises again but the height to which it is carried should not be excessive else the upper incisive muscle, when contracting, will displace the denture. Finally c 32 CLINICAL DENTAL PROSTHETICS From here it rises slightly to cross the narrow posterior edge of the mylohyoid muscle which sometimes is sufficiently well defined to produce a definite notch in the periphery in this region (see figs. 33 and 34). Tig. 34. -Diagram through and molar region ol a "lower denture, illustrating the relation of the lingual flange to the mvlohyoid muscle. Fig. 35. - Diagram through the tst molar region of a lower denture, illustrating the relation of the lingual flange to the tongue, the sublingual gland and the mylohyoid muscle. Dotted line indicates the slope of the lingual flange. APPLIED ANATOMY 33 From this point forwards the periphery usually follows a gentle curve with the concavity looking downwards, dictated by the body of the sublingual gland which lies immediately underneath the mucous membrane forming the floor of the mouth ( see figs. 33 and 35). When it reaches the first premolar region it descends again for a short distance and then rises to clear the lingual frnenum which sometimes presents a very broad attachment to the mandible (see fig. 36). of the lowe r denture. The polished lingual surface of the lower denture slopes downwards and inwards so as to present no area which over- hangs the tongue {see fig. 35). The Upper Denture The periphery of the upper denture commencing with the posterior edge is as follows: This edge, as already pointed out, should sink slightly into the non-movable tissues of the soft palate following a line from the hamular notch of one side to that of the other close to the foveae (see fig. 23). The posterior border then traverses the hamular notch and rises up into the sulcus on the buccal side of the tuberosity (see fig. 30). The height to which it rises is deter- mined by the attachment of the buccinator muscle in this region. From this point it commences to descend following the buccinator attachment, the lowest point of this descent being at the root of the zygoma (see fig. 30). The zygoma having been cleared, the periphery rises again but the height to which it is carried should not be excessive else the upper incisive muscle, when contracting, will displace the denture. Finally c 34 CLINICAL DENTAL PROSTHETICS the periphery is shaped to clear the labial fraenum ( see fig. 28). The polished buccal surface of the upper denture should be hollowed slightly with the concavity looking downwards and outwards so that the buccinator muscle when contracting may press the denture upwards (see fig. 37). Care should always be taken to ensure that the buccal flange in the second molar region is not excessively thick in cases with well-developed ridges since the coronoid process may strike against the flange when the mouth is opened causing soreness of the cheek or dropping of the denture. Fig. 37. - Correct contouring of polished buccal surface upper denture. The orbicularis oris muscle when contracting to press the lips against the teeth does not affect the upper denture as much as it docs the lower because of the greater stability of the former. Therefore, the upper front teeth may be placed sufficiently far forward in most cases to suit the aesthetic requirements of the case and thickening of the labial flange to plump out the lips may be tolerated provided it is not carried to excess. The Peripheral Musculature in Relation to Impression Taking Trays used for impression taking should have a similar outline to that described for dentures. The commonest fault found in stock trays is that they are overextended and especially is this the case with the disto- buccal region of lower trays. Overextended trays lead to overextended impressions and this means that the muscles surrounding the oral cavity have APPLIED ANATOMY 35 been forcefully pushed out of the way and dentures made to such overextended impressions will be displaced by the muscles returning to their normal positions (see fig. 38). Particular attention should be paid to the posterolingual flanges of the lower tray because if these are overextended they will push the floor of that part of the mouth and the palato- glossus muscles downwards and backwards. On the other hand, if the flanges are short the lateral borders of the tongue will get under the tray and spoil the impression ( see fig. 39). The Tongue The Rest Position of the Tongue The dorsum rests against the roof of the mouth and the tip of the tongue rests in contact with the lingual surfaces of the lower incisor teeth. 36 CLINICAL DENTAL PROSTHETICS (4) Short lingual flange of a lower tray trapping the tongue beneath its edge. The lateral borders He against the lingual borders of the posterior teeth and protrude slightly into the free-way space between the occlusal surfaces of the upper and lower teeth. Posteriorly the soft palate rests on the dorsum of the tongue during normal nasal breathing. When the teeth are extracted the tongue spreads laterally and the lips and cheeks fall in to meet it so filling between them the space left by the teeth, termed the neutral zone. The Functions of the Tongue Excluding taste, these are twofold. It controls the food during mastication and swallowing. It controls and directs, with the aid of the lips, teeth and palate the vibrating air stream from the larynx to form the sounds of articulate speech. During mastication it performs as follows: As the piece of food is being incised it controls and steadies it with its tip. In the case of food which does not require incising the tongue is protruded slightly and its centre de- pressed to form a shallow concavity into which the food is placed. Next the food is quickly transferred backwards along the depressed surface of the tongue by a series of muscular waves until it has reached a level with the teeth by ■which it is to be chewed. Hard food is placed farther back than soft or fibrous food because the mandible is a lever of the third class and the farther back the food is placed the shorter is the arm of the lever. APPLIED ANATOMY 37 The middle of the tongue now rises and forces the food laterally between the occlusal surfaces of the teeth which have parted to receive it. The lateral borders of the tongue at this time are on a level with the occlusal surfaces of the lower teeth and pressed hard against their lingual aspects so as to prevent the food passing downwards between the teeth and the tongue into the lingual sulcus. The teeth occlude, dividing the food some of which is squeezed out, some lingually and some buccally. The tongue depresses in the centre gradually to receive the food as it is forced lingually by the occluding teeth and then returns it to them again as they separate. The cheek controls and replaces the food displaced buccally. This cycle, smoothly continuous, proceeds until the food has been adequately divided and insalivated. The tongue then collects the food and forms it into a bolus which it holds in its central depression. A series of waves travelling posteriorly along the tongue then passes the food backwards. As the bolus reaches the back of the tongue the soft palate rises and the tongue and the palate holding the bolus between them pass it into the pharynx whence it is directed over the epiglottis into the oesophagus. Finally the tongue scavenges the sulci with its tip to clear the mouth of fragments of food which have escaped the formation of the bolus. From the foregoing it will be realized that the tongue is a powerful factor mitigating against the stability of fhe lower denture because of its power and latitude of movement. Care must be taken, therefore, to design the dentures so that they impede the movements of the tongue as little as possible and, to gain this end, attention must be paid to the following: (i) The teeth must never be set inside the ridge or they will cramp the tongue causing movement of the dentures and irritation to the patient (see fig. 40). In cases where dentures have been worn for some time the tongue space should be carefully measured from the old dentures and copied in the new ones. ( See chapter on Setting Up and Immediate Dentures.) 38 CLINICAL DENTAL PROSTHETICS FlC. 40. — The tongue cramped. (2) The lower denture should present lingual flanges to the tongue which slope slightly inwards from above down- wards (see fig. 35). In no circumstances should the lingual cusps of the posterior teeth overhang the tongue (r«fig. 41). In other words no concavities should be presented to the tongue into which its lateral borders can expand and so lift the denture. (3) The palate of the upper denture should be as thin as is commensurate with the strength of the material used in its construction. (4) The occlusal plane of the lower denture should be kept low, this allows the lateral borders of the tongue to rest upon the occlusal surfaces of the teeth when the mouth is opened to receive food and so prevent the lower denture from rising [see fig. 42). The Tongue as a Controlling Influence Observation of individuals who wear full dentures satisfactorily, discloses that the tongue is used very largely to control the dentures. It acts in the following ways: APPLIED ANATOMY 39 (1) The dorsum is pressed against the back of the upper denture to prevent it dropping when incising (see fig. 43). (2) The tip is pressed forwards and downwards against the anterior lingual surface of the lower denture when the lower lip tends to force the denture backwards (see fig. 43). (3) The lateral borders of the tongue rest on the occlusal surfaces of the lower denture when opening the mouth (see fig. 42). (6) Low occlusal plane allows the tongue to rest on the occlusal surface. Such control takes time for wearer* of new dentures to master, and a small percentage never learn at all. Attention to the design discussed earlier in this section gives patients a better chance of learning this control. The Tongue in Retching and Nausea Anything held on the anterior two-thirds of the tongue is under complete control and can be manipulated by the tongue at will and, if necessary, ejected from the mouth altogether. Once it has passed on to the pharyngeal part of the tongue, however, this ease of control is lost and, if it is required to eject a foreign body, an ejectory contraction of the muscles forming the pharyngeal sphincter, termed retching, must occur, and the foreign body is then forcefully expelled. APPLIED ANATOMY 41 Wearing dentures during sleep is to be recommended during the learning period for a very similar reason because tolerance is gained by the tongue during the night. If the dentures are removed before retiring the tolerance gained during the day is lost and the early morning is a time when many people are especially susceptible to retching. * 10. 44 (a) Showing posterior edge of upper denture correctly post-dammed. {b) Thick square edge of upper denture incorrectly post- dammed. The Temporo-mandibular Joint The Normal Position of the Condyle When the natural teeth are in centric occlusion (this term is discussed in Chapter VI), the anterosuperior aspect of the head of the condyle should articulate through the agency of the meniscus with that part of the fossa formed by the squamous temporal bone {see fig. 45). When the mouth is opened or the jaw protruded or moved laterally, the condyle should travel down the articular eminence and, in the widest position of opening, rest just short of the crest of the articular tubercle. The Muscles of Mastication The muscles of mastication when contracting are capable of applying a force of over 400 lb. between opposing molar 42 CLINICAL DENTAL PROSTHETICS I'm. 45. -The relation of the head of the condyle to the fom - (a) When the mouth n closed. teeth. This is very greatly reduced when artificial dentures arc fitted because the mucous membrane cannot stand such pressure, a figure of 30 lb. never having been recorded. The mandible, its joints and the muscles of mastication together constitute a double lever of the third class {see fig. 4G). The muscles which apply the powerful closing force to the mandible arc the temporalis and the masseter and it is thus obvious that the farther back in the mouth (i.c. the nearer to the insertions of these muscles) a piece of food is placed the greater the power which can be brought to bear on it. APPLIED ANATOMY (6) When the mouth is open. POWER _J WEIGHT FULCRUM 44 CLINICAL DENTAL PROSTHETICS Muscular Power and Vertical Dimension The beautiful control and co-ordination existing between the muscles of mastication enables them to apply their great power to a piece of food and yet bring the teeth into occlusion after its division with such fine control that no jarring occurs. They are enabled to do this because the position of the teeth and jaws in space at any moment is accurately transmitted to the controlling centres in the brain by nerve endings in the muscles, mucous membranes, tongue and periodontal mem- branes. Such delicate control is only possible, however, provided the occlusal surfaces of the teeth, in their relation to the jaws and muscles, is not suddenly altered. The reader will no doubt be personally familiar with the sudden alteration of this smooth cycle when normal jaw closure is prevented by the presence on the occlusal surface of a tooth of a piece of lead shot found when eating game or rabbit. The premature occlusion of the teeth through the agency of the unyielding shot is so powerful that it causes great shock and discomfort and occasionally fractures the tooth on which the shot is resting. From this it will be obvious that if dentures arc fitted which increase vertical dimension the premature occlusion of the teeth which occurs will be so powerful as to cause both dis- comfort and damage to the underlying tissues. It may be stated here that one of the commonest causes of failure of dentures results from the fact that they are constnictcd to a slightly increased vertical dimension. It is claimed that the absorption of the ridges resulting from the force of occlusion occurring with an excessive vertical dimension soon reduces its height and restores equilibrium. It is doubtful, however, whether many patients would tolerate such a method of reducing their vertical dimension and, even if they did, the denture bases would no longer fit the new form of the absorbed ridges. The muscles of mastication develop their greatest power within a short range of the normal vertical dimension, and if this dimension is reduced much below that which is norma! considerable loss of power occurs. In certain cases presenting difficulties in the stability of the dentures, advantage may be taken of this power loss associated APPLIED ANATOMY 45 with closure of the vertical dimension to reduce the forces applied to the dentures. Such closure of the vertical dimen- sion, however, should be carried out with care and a full realization of the other disadvantages which may accrue; these are discussed elsewhere in the booh. Muscle Tone and Antagonism In a normal mouth with a complete complement of natural teeth the elevator, depressor, protruder and retractor groups of muscles, or more accurately muscle fibres, balance one another and gravity and so control the movement of the mandible with great precision. For example in protrusion the lateral pterygoid muscles draw the head of the condyle and the articular disc forwards, the medial pterygoid muscles produce a strong component force pulling the angle of the mandible forwards, the superficial fibres of the masseter muscle and to a slight extent the anterior fibres of the temporalis muscle also bring a forward traction to bear on the mandible. When posterior teeth are present the forward pull of these muscle fibres is accurately balanced by the gradual relaxation of the posterior fibres of the temporalis muscle and some of the deep fibres of the masseter. In retrusion the reverse action occurs. When the posterior teeth are lost and mastication is performed entirely on the front teeth or when a long period of edentation precedes the fitting of full dentures, abnormal habits of chewing with the mandible forward are acquired which results in the delicate balance between the protruding and retruding groups of muscle fibres being temporarily lost, the protruding group becoming dominant due to excessive use. In such cases difficulty may be anticipated when registering the anteroposterior bite relationship, and great insistence must be placed on complete muscular relaxation and a very gentle closing movement thus tending to eliminate the dominance of the protruding group of muscle fibres in such cases. The Freeway Space When the mandible is at rest it is supported by the elevator group of muscle fibres which are not fully relaxed but are in a condition of partial contraction, termed tonus, which is 4^ CLINICAL DENTAL PROSTHETICS sufficient to counterbalance comfortably the tonus of the depressor muscles of the mandible, and gravity. The position which the mandible assumes when at rest is probably constant for each individual and normally when it is in this position the occlusal surfaces of the maxillary and man- dibular teeth are separated by 2-4 mm (* in.). This space betw ccn the occlusal surfaces of the teeth is termed the freeway space and its importance in gauging the vertical dimension is dealt with in Chapter VI. The Lip Muscles The orbicularis oris closes the lips and when contracting, its lateral insertions into the modeoli are fixed by the contraction of the quadratus labii superioris and inferioris, zygomaticus, triangularis, and buccinator muscles. The incisal muscles also fix it to the alveoli. During such function considerable inward pressure is brought to bear on the labial surfaces of the teeth and also the labial sulci are reduced in depth. The upper denture, due to its inherent stability, can withstand such pressure provided its labial flanges have not been overextended. The lower denture, however, in cases presenting poorly formed alveolar ridges is likely to be raised from the ridge in front and pushed backwards. Experienced denture wearers counteract this pressure of the lip by a forward pressure of the tongue but assistance can oficn be given to the tongue by carrying the heels of the lower denture up the ascending rami of the mandible in such cases. The effect of the modioli on denture design has already been discussed. The elevator and depressor muscle groups antagonize the orbicularis oris and one another thus opening the lips and pro- ducing facial expression. It must be remembered, when closing the vertical dimens'.on, that the origins of the elevator and de- pressor groups of muscles wall be moved closer together thus causing a bunching up of the muscles with consequent loss of tone. This causes drooping of the mouth, puckering and wrinkling of the skin of the lips and face and a flattening of the philtrum giving an aged and bad tempered appearance. Some of this damage can be mitigated by plumping the lateral labial flange of the upper denture ( see fig. 47) thus causing the muscles of the CLINICAL, DENTAL PROSTHETICS 46 sufficient to counterbalance comfortably the tonus of the depressor muscles of the mandible, and gravity. The position which the mandible assumes when at rest is probably constant for each individual and normally when it is in this position the occlusal surfaces of the maxillary and man- dibular teeth are separated by 2-4 mm ( Jin. ).This space between the occlusal surfaces of the teeth is termed the freeway space and its importance in gauging the vertical dimension is dealt with in Chapter VI. The Lip Muscles The orbicularis oris closes the lips and when contracting, its lateral insertions into the modeoli are fixed by the contraction of the quadratus labii superioris and inferioris, zygomaticus, triangularis, and buccinator muscles. The incisal muscles also fix it to the alveoli. During such function considerable inward pressure is brought to bear on the labial surfaces or the teeth and also the labial sulci are reduced in depth. The upper denture, due to its inherent stability, can withstand such pressure provided its labial flanges have not been overextended. The lower denture, however, in cases presenting poorly formed alveolar ridges is likely to be raised from the ridge in front and pushed backwards. Experienced denture wearers counteract this pressure of the lip by a forward pressure of the tongue but assistance can often be given to the tongue by carrying the heels of the lower denture up the ascending rami of the mandible in such cases. The effect of the modioli on denture design has already been discussed. The elevator and depressor muscle groups antagonize the orbicularis oris and one another thus opening the lips and pro- ducing facial expression. It must be remembered, when closing the vertical dimension, that the origins of the elesator and de- pressor groups of muscles will be moved closer together thus causing a bunching up of the muscles with consequent loss of tone. This causes drooping of the mouth, puckering and wrinkling of the skin of the lips and face and a flattening of the philtrum giving an aged and bad tempered appearance. Some of this damage can be mitigated by plumping the lateral labial flange of the upper denture (see fig. 47} thus causing the muscles of the 48 CLINICAL DENTAL PROSTHETICS elevator group to follow a longer course from origin to insertion and so restoring their tone, but the only true cure is to restore the height of the bite. The Mandibular Movements of Mastication The natural teeth are embedded in bone to which they are attached by means of the fibrous periodontal membrane, whose resilience may here be disregarded. The bones comprising the upper jaw move only with the skull and so may be regarded as the fixed factor whilst the lower jaw, which is attached to the skull by the two very mobile tcmporo-mandibular joints, is capable of many complicated movements. It is these move- ments together with those of the surrounding muscles which are of such importance to the prosthetist. The temporo-mandibular joint is unique because some muscle fibres are attached to the intracapsular disc which is thus moved during function in its relation to the bones which articulate on either side of it (see fig. 45). The fact that the intracapsular disc itself moves has a pronounced and peculiar effect on the movements of the mandible which is unable, except within very strict limits, to move with a pure hinge rotation; it is forced to move forwards when moving downwards. The normal articulation of the anterior teeth in most Europeans and Americans is with the uppers slightly anterior Ftc. 48 APPLIED ANATOMY 49 to the lowers and overlapping them by j mm. to 4 mm., a fact which must be borne in mind when considering normal mandibular movement. The overlap in the horizontal plane is termed the oveijet and that in the vertical plane the overbile (see fig. 48). Now to consider what happens when a piece of food is bitten olf, chewed and swallowed (see fig. 45). ' 7 Tio. 49. — Opening and incising movements of the mandible. (a) Opening movement - cond) les rotate and move forwards to bring incisors into vertical relationship. First Movement - The Opening Movement The first movement of the mandible, which is confined to the lower articular cavity of the joint, is a pure rotation of the 5 ° CLINICAL DFNTAL PROSTHETICS condylar heads against a stationary disc. It is mainly produced by gravity and the contraction of the anterior belly of the digastric muscle but the jaw is prevented from dropping too suddenly by the gradual relaxation of the temporalis and masseter muscles. From this point the mandible commences to move forwards by the contraction of the lateral and media! pterygoid muscles, the condylar heads and discs moving down- wards and forwards along the articular eminences, this move- ment occurring in the upper joint cavity. The condyle heads are still able to rotate in relation to the discs thus controlling the vertical relationship of the teeth though not the anteroposterior. Second Movement — The Closing Movement When the upper and lower front teeth have parted sufficiently. APPLIED ANATOMY r«o. 49. - ( e ) Teeth meet and lower inciion slide with shearing action up palatal inclines of upper incisors until heads of condvles arc physiologically retruded in glenoid fossae. the food to be bitten off is placed between these tcetlt and the reverse movement back to centric occlusion takes place beginning with some degree of approximation of the incisive edges depending on the resistance offered by the food. This is brought about by the contraction of the masseter and medial pterygoid muscles and results in a crushing rather than a cuttingaction. Third Movement - The Shearing Movement The final return of the teeth to centric occlusion is the result or further contraction of these muscles and by the posterior fibres of the temporalis accompanied by gradual relaxation of the pterygoid muscles. This muscular synergy returns the condyle heads and discs to the rest position in the glenoid fossae at the same time producing a shearing action between the incisive edges of the teeth. 5 2 CLINICAL DENTAL PROSTHETICS These movements have been described as though of equal degree on both sides, but of course this is not so and invariably one side moves more than the other thus producing a lateral movement which increases the shearing action of the incisive edges of the teeth. It must also be remembered that there is great individual variation in mandibular movement but only the average general movements can be described here. Fourth Aloiement - The Lateral Movement Chewing The morsel of food in the mouth must be broken up and insalivated before being swallowed and the posterior teeth are used for this purpose. The food is placed between the occlusal surfaces by the tongue and is held there by the lateral pressure of the tongue on the one side and the cheek on the other. The first few movements arc usually those of simple opening and closing which reduce the food to small pieces before the actual chewing begins. Chewing movements approximately conform to the following pattern which is, of course, smoothly continuous although described in stages. There is also much greater individual variation of these lateral movements than of the incisive ones just described, owing to the prevalence of malposition of the teeth and cuspal interference found in the civilized races. Chewing begins with a simple opening movement and the placing of the food on the occlusal surfaces of the posterior teeth on one side, called the working side. There is then a lateral rotation of the mandible towards the working side which is brought about by the condylar head and disc of the opposite side being pulled downwards and forwards on the articular eminence by the lateral pterygoid muscle. At the same time the condylar head on the working side rotates about a sertical axis and moves slightly backwards and laterally by contraction of the masseter and temporalis, thus causing a slight but definite lateral shift of the whole mandible. This movement is called the Bennet movement. The mandible now moves upwards in this lateral position until considerable resistance is encountered or until the opposing cusps, having penetrated the food, come into contact with each other. The APPLIED ANATOMY 53 FlO. 50. - The chewing c)tfe. final movement is the upward and sideways return to centric occlusion and it is during this last small movement that the cutting and tearing of tough fibres and the crushing and grind- ing of hard particles takes place between the approximating cusps (see fig. 50). Chapter III HISTORY TAKING AND EXAMINATION OF THE MOUTH Success in full denture prosthetics depends on three factors: (1) The patient’s attitude to dentures and his ability to learn to use them. (2) The condition of the mouth. (3) The skill of the operator who must acquire all the informa- tion he can, in order to anticipate difficulties which may arise and select the technique best suited to overcome them. He must be in a position to warn a patient of expected difficulties, not only in order to gain his co- operation and later perseverance, but also to save himself from possible recriminations when dentures, constructed for abnormal conditions, do not appear to the patient to be as comfortable or efficient as those of his relations or friends. Finally, though of the greatest importance, he should be able to recognize the oral symptoms of such general systemic diseases as syphilis, pernicious anaemia, malignant tumour and in fact any other oral manifesta- tions since he will sometimes see these conditions before a medical practitioner has been consulted. History taking and examination of the mouth will be described separately, but this is only for convenience and it must be realized that in practice they are inseparable. For the same reasons of convenience the patient’s mental attitude will be discussed when describing history taking. The usual method, in medicine, of describing the information obtained about a patient is to say that it is made up of signs and sym- ptoms, a sign being a fact which the investigator finds for himself, and a symptom something which is told him by the patient. 54 EXAMINATION* OF MOUTH: HISTORY TAKING 55 1. History Taking This will be described under separate headings merely for convenience and frequently runs concurrently with the examination of the mouth. It should be directed towards discovering those aspects of the ease which cannot be obsened and augmenting, where necessary, those which can. (a) The Patient’s Attitude to Dentures Although it is true that nearly all edentulous people who go to consult a dental surgeon want to have dentures, it must not be assumed that they arc all equally willing to play their part in making such dentures successful. An attitude of mind will have been formed by the patient’s own past experience or dentures, if any, or from his observation of friends or relatives who wear dentures. If, prior to being rendered edentulous, a partial denture was worn with comfort and efficiency, the same will be expected of full dentures. It should be explained to such patients that, although partial denture experience is helpful in relation to full dentures, the latter require a considerably greater degree of control because they arc not, as were the partial dentures, retained or supported by the natural teeth. If this difference in the two types of denture is not explained, the initial difficulty experienced in learning to use the full dentures compared with the partial dentures may cause the patient much disappointment, and he may condemn the dentures as being faulty, not knowing that a little perseverance is necessary. If full dentures arc already being worn and they have been comfortable and efficient, die same will be expected of the new* dentures. If the old full dentures were troublesome, the attitude may be expectant of better results with the new dentures or pessimism that nothing better can be hoped for. If no previous denture experience exists, friends or relations may have coloured the patient’s mind with their own attitudes. In such eases the efficient control and use of full dentures depends to a very large extent on the formation of new habits, and a new* pattern of muscular movement. This demands time and some patience on the part of the wearer. Many full denture troubles can be traced to the fact that no preparation 5^ CLINICAL DENTAL PROSTHETICS of the patient’s mind preceded the fitting of the dentures. If a leg is amputated the patient anticipates a long learning period before he can walk confidently with its artificial substitute, and he never expects to be able to walk as well with it as he did with his natural leg. In addition he is taught to use the artificial limb and this learning period may extend over several months. It is necessary, therefore, that the correct attitude to full dentures be instilled into the patient’s mind. This cannot be done in a few minutes as the patient is being shown out of the surgery at the final visit; it should be a gradual process spread over all the visits necessary' to complete the dentures, and should be related to the attitude already existing in the patient’s mind. The patient should be told what to expect when he com- mences to wear the dentures; how long the period of learning is likely to be; how considerable perseverance will be required before any degree of skill is attained in their use. This prognosis will bear a very definite relationship to what is discovered during the history taking and mouth examination. (b) The Existence of Old Dentures Most patients volunteer information about the existence of old dentures even if it is not already obvious, but every edentulous patient who does not mention old dentures of his own accord should be questioned concerning them. Questions are directed to elicit information regarding the length of time dentures have been worn; how many sets have been made since the teeth were extracted; the success of the existing or old dentures and the attitude of the patient to their appearance. All this information is important because if the existing dentures have been satisfactory' and only the passage of time has made them ill-fitting, any gross alteration of the new dentures trill almost certainly mean their failure. A person who has worn comfortable and efficient dentures has developed a complete control of them which is entirely reflex and is dependent on a subtle appreciation by the tongue, cheeks and lips of the shape and position of the polished surfaces of the dentures, the height of the occlusal plane and exactly when the teeth will make contact. If any of these is altered grossly or EXAMINATION OF MOUTH: HISTORY TAKING 57 suddenly the established reflexes are upset and conscious control of the dentures must again be exercised. With an experienced denture wearer such control is a thing of the past, and if it can be dispensed with by copying certain aspects of the old dentures success with the new dentures is assured. If on the other hand certain alterations in the new dentures are essential, e.g. altering the occlusal plane for reasons of appear- ance or restoring the correct vertical height to correct an over- closure, then this must be explained to the patient and he must be told that conscious control of the new dentures will be required until new reflex habits are formed. (c) Information Regarding the Loss of the Natural Teeth If the teeth were not extracted by the dental surgeon who is constructing the dentures information regarding their extrac- tion should always be sought. A history of difficult extractions should be followed by a radiographic examination of the jaws to verify the absence of retained roots. Questioning should be directed to eliciting the general order in which the teeth were lost. For example, if a]] the posterior teeth were extracted some years before the anterior ones and no partial dentures were worn in the meantime, then a habit of eating with the front teeth will have been formed which, if persisted in, will have a pronounced unstabilizing effect on full dentures. A similar condition will exist in individuals who have been edentulous for a considerable length of time and have not worn dentures, for thus they are only able to approximate their jaws in the anterior region and consequently forward travel of the mandible is necessary all the time during eating. When there is a history of abnormal mandibular function or movement, then difficulty can be anticipated when register- ing the anteroposterior occlusal relationship. () the itmtinc. The jaw relationship in different cases u'iJJ van* from normal lo inferior protrusion on the one hand to inferior retrusion on the other {ste fig. 56). It is important to gain some knowledge of the jaw relationship at an early stage so that possible difficulties may be foreseen* the rims of the record blocks constructed in their correct positions and the set-up and occlusion of the teeth related to the individual case as discussed later in the book. (c) StiArr. or the Hard Palate When considered in conjunction with the alveolar ridges, the experienced operator is able to judge with considerable accuracy any unusual difficulties the patient is likely to experience in the retention of his dentures and should inform him of them at this early stage {ur Chapter II for details). (rf) Depth of the Sulci Whenever a very shallow sulcus is encountered a special impression technique will he required in order to obtain an adequate peripheral seal and so utilize atmospheric pressure to the full as a retentive force (see Chapter IT for details). (c) lNTF.Rtr.RF.NCF. FACTORS The size of the tongue, tightness of the lips and any abnormal 66 CLINICAL DENTAL PROSTHETICS A C / y\ Fig. 56. - Line diagram showing jaw relationships in sagittal section : (a) Normal. (b) Inferior retrusion. (c) Inferior protrusion. muscular or fraenal attachments must be noted as they will influence the design of the future dentures and the type and position of the artificial teeth used (see Chapter II for details). (J) Unextracted Roots These may be seen flush with, or protruding above, the surround* ing mucous membrane (see fig- 57)> or without an obvious EXAMINATION OF MOUTH! HISTORY TAKING 67 area of inflammation round them. They may be loose or firm, and in the latter case it is always wise to take an X-ray photo- graph. Rarely should a denture be made covering unextracted roots, but in the very exceptional cases where it must be done, the denture should be freely relieved over them, otherwise it is likely to rock and probably fracture. (g) Sinuses An infected area in the bone, such as surrounds the retained broken-off apex of a tooth, usually communicates with the surface through a channel known as a sinus (see fig. 57). Fig. 57 (а) Root visible on surface. (б) Buried root with sinus communicating with buccal sulcus. (c) Enlarged \iew of sinus. The appearance in the mouth is usually that of a very small nipple-shaped elevation with a hole in its centre, most commonly found on the sulcus side of the ridge. Pressure with the finger, above in the upper and below in the lower, directed towards the opening will cause the extrusion of a droplet of pus or serum in most cases; this is usually diagnostic and whenever seen should be followed by an X-ray photograph to locate the position and extent of the infected area. (A) Unilateral Swellinos Any abnormal swellings in the mouth must be investigated and diagnosed, and when found only on one side they are much more likely to be pathological than when they arc bilateral. 68 CLINICAL DENTAL PROSTHETICS 3. Digital Examination Before starting to explore the mouth with the finger tips the patient should be asked to indicate immediately if any pain is felt and the cause of such pain must be found. Any area which is painful to the pressure of a soft finger is unlikely to tolerate the pressure of a hard denture. (a) Firmness of the Ridges This is most conveniently tested by placing a finger on each side of the ridge and applying alternate lateral pressure. Ridges vary in firmness; the normal is composed of bone covered with a thin layer of mucous membrane, others may appear the same but it may be found that the bone has been absorbed and the mucous membrane is thickened and con- tains much fibrous tissue which is displaced by the lateral pressure test. Flabby, fibrous ridges may be encountered in all parts both of upper and lower jaws, but probably the most common position is in the upper anterior region and the history in these cases is almost invariably one of loss of all the natural teeth except the lower antcriors. Later, owing either to the failure to wear a partial lower denture or to the wearing of an inefficient denture, the patient acquires the habit of eating entirely on the anterior teeth with resultant torsion on the upper full denture which leads to rapid absorp- tion of the anterior alveolar ridge and its replacement by fibrous tissue (see fig. 58). ( b ) Irregularities of the Alveolar Ridge The general size and shape of the ridges will be noted during the visual examination, but palpation will be necessary to determine irregularities of the underlying bone. The informa- tion sought is quite apart from that discussed later under the heading of ‘hard and soft areas’ and is directed at determining the shape and regularity of the underlying hard tissues. Alveolar absorption is never uniform and hard nodules, sharp edges, spikes and irregularities are frequently felt and pain on pressure over these areas is common ( see figs. 59 and 60). The prosthetist must at this stage decide whether surgical EXAMINATION OF MOUTH: HISTORY TAKING 69 membrane. correction is needed, or whether they will remedy themselves in time in the course of normal absorption, or whether relief of the denture alone will be satisfactory. (c) Variations of Mucous Membrane The ideal mucosa on which to seat full dentures should be: (i) Firmly bound down to the sub-adjacent bone by union with the periosteum which will thus prevent the denture and mucosa moving together in relation to the supporting bone. (ii) Slightly Compressible . - This will allow the denture to bed comfortably into place because the mucosa -will adjust itself slightly to the fitting surface of the denture: this will very materially increase the retention by adhesion and cohesion because the film of saliva between the denture and the mucous membrane will be very thin. It will also allow maximum retention from atmospheric pressure because the denture bedding slightly into the tissue will prevent air leaks. In addition such mucosa will act as a cushion to the normal stresses of mastication and prevent the development of sore spots and painful areas from pressure on the underlying bone. (iii) Of an Even Thickness. - This condition is never realized because in a normal mouth the membrane on the crest of the ridges covers scar tissue resulting from the extraction of the teeth, and this varies in thickness. Fto. Go - Rough irregular surface of alveolar ndge ut 4$*r{ In the mid-line of the palate the membrane is thinner than elsewhere. The sides of the vault of the palate are traversed by the anterior palatine, nasopalatine and greater palatine arteries and veins and these are protected by a layer of sub- EXAMINATION OF MOUTH.' HISTORY TAKING 71 mucous connective tissue and fat {see fig. 61). The tissue of the retromolar pad is often much thicker than any other lower ridge tissue. Fio. 61. -This coronal diagram through the ist molar region illustrates the varying thickness of the mucous membrane covering the oral structures. Where the differences in compressibility of the mucosa are not great or of large extent they will be found to be clinically unimportant, but where the reverse conditions are present the prosthetist will need to have recourse to a special impression technique or alteration in normal denture construction. Thin mucosa covering a well-defined torus palatinus and flanked by thick, compressible membrane, -will result in a denture which rocks during function, causing pain to the patient and frequently fracture of the denture due to the repeated flexure the base is required to undergo during mastication {see fig. 62}. (rf) Maxillary Tuberosities These may be found on visual examination to be bulbous and to have a definite undercut area above them, but only by palpation can it be determined whether the bulbous portion is composed of hard or of soft tissue, that is, whether Fig. 63 (a) A buccal undercut formed b> soft ti«i (J) A buccal undercut formed b> bone. EXAMINATION OF MOUTH: HISTORY TAKING 73 but in this region it is sometimes possible to carry the denture into the undercut area below and behind the ridge. In the majority of cases these ridges are felt to be pronounced and sharp, which is a contra-indication for extending the denture over them, unless the denture is relieved, but where they (eel ill-defined and rounded a lingual extension is usually successful [see fig. 64). Fic. 64 (u) Sharp mylohyoid ridge with lingual flange of denture finished above the ridge. ( 4 ) Rounded mylohyoid ridge which may allow the lingual flange of the denture to be earned beneath the ridge. (/) Lingual Pouch This is the area bounded medially by' the tongue, laterally by the mandible, posteriorly by the palatoglossus muscle and anteriorly by the posterior 3 mm. of the mylohyoid muscle. The extent of the pouch with the tongue at rest and with the tongue protruded sufficiently to lick the lips and also during the act of swallowing should be noted. This is most conveniently done by gently inserting the index finger into the pouch and asking the patient to perform the above actions when the alterations in the extent of the pouch can be felt. If a pouch persists during tongue movement and swallowing then the lingual flange of the denture can probably be carried into this area which will materially assist in the retention of the lower denture. 74 CLINICAL DENTAL PROSTHETICS (g) Painful Areas This is not a separate examination of itself and pressure pain may be encountered during any of the digital examinations already mentioned. The whole of the denture-bearing mucous membrane should be palpated and any painful areas must be diagnosed and treated before successful dentures can be constructed. 4. X-ray Examination Ideally a full mouth X-ray examination should be made of every edentulous patient prior to starting denture construction, otherwise a certain number of pathological or abnormal con- ditions will pass unrecognized, as for example buried roots and unerupted teeth. When it is considered that this routine is uneconomic or too time-consuming, X-ray photographs should still be taken to confirm or assist in diagnosis in the following cases: (i) Buried roots. (ii) Sinuses. (iii) Unilateral swellings. (iv) Rough alveolar ridges. (v) Areas painful to pressure. The information which has been given in this chapter is now tabulated ( see opposite page) for the convenience of the beginner. EXAMINATION OF MOUTH: HISTORY TAKING 75 f Examinations iformation< History < Visual s f Unilateral swellings Sinuses Unextracted roots Interference factors Depth of sulci Shape of hard palate Size and shape of ridges Size and shape of arches Colour of mucous membrane Firmness of ridges Shape of alveolar ridges Maxillary tuberosities Mylohyoid ridges Painful areas Hard and soft areas Mental attitude Old dentures Extractions Age Occupation Aesthetics Painful areas Digital Chapter IV SIMPLE SURGICAL PREPARATION OF THE MOUTH The Object of Surgical Preparation The object of surgical preparation of an edentulous mouth is to render the denture-bearing area as satisfactory as possible from the aspects of health, comfort and shape. Only rarely is this beyond the scope of the average dental surgeon. In a large number of cases small alterations could be made to a mouth which might benefit the patient slightly or make things a little easier for the prosthetist, but it must never be forgotten that even the most minor surgery involves cutting living tissue and is rightly feared by nearly everyone, and so should never be lightly undertaken. A very safe rule is never to advise surgical interference unless convinced that the benefits resulting from it will outweigh the risks and discomforts. Conditions Requiring Surgery The following conditions, all of which are frequently met are well within the scope of a dental surgeon for operation: (1) Buried roots. (2) Unerupted teeth. (3) Dental cysts. (4) Ridge irregularities. (a) Feather-edge ridge. ( b ) Knife-edge ridge. (c) Unabsorbed areas and bone nodules. (d) Undercut areas. {e) Over-prominent tuberosities. (/) Flabby, fibrous ridge. (5) Over-prominent fraena. (6) Denture hyperplasias or denture granuloma ta. (7) Enlarged torus, either maxillary or mandibular. The first three conditions in the above list, being of general 76 SIMPLE SURGICAL PREPARATION OF MOUTH U dental application rather than purely prosthetic, will not be mentioned further except to stress that they should almost invariably be dealt with before denture construction is begun. General Surgical Principles Before outlining the techniques of individual operations a few general principles are given. (1) Asepsis must be observed. Since it is quite impossible to sterilize the oral cavity it is perhaps not immediately apparent why sterility' on the part of the operator is so essential. Every' healthy animal has acquired a high degree of immunity to the bacteria normally present in its mouth. If a dog injures itself it licks the wound and although its saliva is teeming with bacteria the wound rarely becomes septic, but if the same dog were to bite a man and he did nothing about cleansing the injury it would almost certainly turn septic. So although a sterile field for operations in the mouth is impossible every care must be taken to prevent the introduction of foreign bacteria. (2) Incisions through the mucopcriosteum must be made with firmness, otherwise reflection without tearing is impossible. (3) Incisions should err on the side of being too long rather than too short; one extra stitch is of no consequence to the patient whilst a little extra vision or space is frequently of great assistance to the operator. In addition, tissue which is well reflected is in less danger of being traumatized during the operation. (4) When operating under local anaesthesia it should be remembered that bone cutting with a hammer and chisel causes much more jarring and discomfort to the patient than cutting with burs. (5) Decide beforehand, as far as possible, what is to be done and be sufficiently radical; results will not be obtained by reflecting the mucous membrane and then just scratching the bone. (6) If there is any doubt whether a flap will stay in place, suture it. A suture is painlessly inserted under anaesthesia and can be painlessly removed a few days later. 78 CLINICAL DENTAL PROSTHETICS Diagnosis of Conditions Requiring Surgery By far the largest numbers of edentulous mouths -which require some surgical preparation for the reception of dentures are those in which there is an abnormal condition of the bony ridges and, whilst the general technique of operating remains the same, the surgeon should differentiate between the various conditions before starting to operate: slight variations in technique will be needed for the different conditions. Feather-edged Ridge This can usually be detected on palpation as a thin, irregular, sharp edge painful to pressure. It is apparently due to irregular alveolar absorption, and as it is most frequently found follow- ing the extraction of teeth for periodontal disease it is some- times wrongly described as residual sepsis. The radiographic appearance is of a very irregular alveolar crest with no clearly defined outline, the bone appearing to fade away ( see fig. 60). On exposing the bone exactly the same picture is seen; it is found to be cancellous in type, uncovered by a cortical layer, the alveolar crest presenting innumerable spicules and irregularities. Knife-edged Ridge On palpation the ridge is felt to be thin buccob'ngually, sharp but smooth and, like the feather edge, painful on pressure. Found only in the mandible it appears to be due to absorption which is greater buccolingually than vertically. X-ray photo- graphs show a thin ridge with a clearly defined outline, the cancellous bone being covered with a cortical layer. The appearance of the exposed bone confirms this (see fig. 65). Unabsorbed Areas and Bone Nodules These can usually be felt as smoothly rounded hard lumps under the mucous membrane and their cause is apparently unknown. Radiographically they show' as small roundish areas of increased density. On exposure the nodules are easily seen as raised lumps of smooth, hard, cortical bone. SIMPLE SURGICAL PREPARATION OF MOUTH 79 Fig. 65. - Sagittal diagram showing knife edge ridge in lower anterior region. Alveolectomy This is the name given to the operation for the removal of alveolar bone, and is equally applicable to the removal of one small nodule or the excision of bone from the entire alveolar ridges of both jaws. This operation is most frequently performed under local anaesthesia as it is both more convenient to work in a dental surgery and is generally preferred by patients. Technique of Alveolectomy The Incision An incision is made just below the crest of the alveolus on the buccal side, and care must be taken that all fibres of the muco- periosteum are severed. This is not always easy if the under- lying bone is rough and irregular, and a heavy scalpel is preferable to one having a light and flexible blade as the cutting edge must be pressed firmly against the bone ( see figs. 66 and 67). Further incisions at each end of this transverse cut will be needed on the labial or buccal surfaces, and these should be continuous with the first incision, joining it in a gentle curve and not at right angles, otherwise the small piece of muco- periosteum in the angle is difficult to retain in place during healing. 8o CLINICAL DENTAL PROSTHETICS Fic. 66. - Alveolectomy of the upper anterior region. The line of the incision. Fic. 67. - Ah colectomy of the upper anterior region. Malting the incision. SIMPLE SURGICAL PREPARATION OF MOUTH 8l The incisions should be carried no deeper into the sulci than is absolutely necessary because the tissues in this area are looser and more vascular than elsewhere and their severance will result in greater post-operative swelling and haematomata. On the lingual or palatal surfaces further incisions are rarely necessary as the soft tissues here will be reflected towards the inner side of the arch where, instead of being stretched, they will have more room. Refection of Tissues The next step is the reflection of the mucopcriosteum with a periosteal elevator, and is often the only difficult part of an otherwise simple operation. The soft tissues are very adherent to the bone and if thin, great care must be taken not to tear them; this is not easy as often considerable force is required particularly when starting to lever up this membrane. This reflection is continued until all the bone to be removed is fully exposed (see fig, 68). Fro. 68. -Alv colectomy of the upper anterior region. Reflection of the mucopcriosteum. 82 CLINICAL DENTAL PROSTHETICS Removal of Bone With a pair of rongeurs the alveolus is trimmed to the desired shape [see fig. 69). Some operators prefer to use large, bone- cutting burs for trimming the alveolar ridge, and with their use a jet of water constantly playing on the bur will be found a great help as it will keep the field clear of blood, saliva and debris. It will also keep the bur from clogging and heating, and the water is easily removed from the mouth by an efficient “sucker”. Fig. 69. - AIv colectomy of the upper anterior region. Removal of bone with rongeurs. Having removed the gross mass of bone it is necessary to smooth the remainder as much as possible with bone files (see fig. 70). The smoothness or othemise of the bone can easily be ascertained, by running the tip of the finger over the area, having first replaced the mucoperiosteum. This last point is very important for these reasons: (1) There is less likelihood of introducing infection. (2) Exposed cancellous bone always feels rough. SIMPLE SURGICAL PREPARATION OF MOUTH 83 (3) Dental surgeons arc accustomed to judging the shape and smoothness of bone through an intervening layer of mucous membrane. When satisfied with the feel of the bone, the debris caused by filing should be washed away by a gentle jet of warm normal saline solution and the flaps of soft tissue replaced. These flaps will be found now to overlap, and they must he trimmed till their edges just approximate without tension. If too much tissue is removed there will be a gap between the edges which must epithelialize over and healing will be retarded, whilst if too little is cut away a thick fibrous band will be left which may well make the later wearing of a denture very difficult. A pair of dissecting forceps to hold the strip being removed and a pair of serrated-edged scissors are the best instruments to use as the wet, fibrous tissue is rather difficult to control and the serrations on the blades of the scissors prevent the tissue slipping. 84 CLINICAL DENTAL PROSTHETICS Suturing The operation is completed by stitching the flaps in place, sufficient stitches being used to make it impossible for the tongue to catch against or lift a flap. The needles should be fine and the sutures of fine gauge silk, and as the object of the stitches is only to hold the parts in place they must never be pulled tight nor should they be placed too near an edge in case they pull out (see fig. 71). Fie. 71.- Alvrolectomy of the upper anterior region. Suturing the raucoperi osteal flap back into position. The patient may now rinse the mouth out gently, and if dentures are worn the)' may be inserted, as they will protect the wound from the inquisitiveness of the tongue and so allow healing in the minimum length of time. Some operators line such dentures where the)' cover the wound with B.I.P. paste, a paste composed of bismuth, iodoform and paraffin, whilst others use penicillin paste in the same way, but neither is usually necessary. The patient may be given two aspirin-phenacetin-codein tablets to take, as the effect of the anaesthetic is being lost, to SIMPLE SURGICAL PREPARATION OF MOUT H 83 minimize any after-pain of the operation. Two more tablets every four hours may be prescribed if pain persists. A mouth- wash is quite unnecessary but if the patient particularly wishes, anything mild and bland such as glycerin-thymol will do no harm. Post-operative Procedure The patient should be seen twenty-four hours later to make sure that there is no undue swelling or pain, though both are usually absent. Three or four days later the stitches may be removed by holding them steady with a pair of tweezers and cutting with a sharp pair of fine pointed scissors or a scalpel. If pain is caused in removing these stitches it is caused by clumsiness or inefficiency on the part of the operator. No attempt has been made to describe the quantity of bone which should be removed, and this omission is deliberate since every case differs and each must be treated according to its individual needs. The general principle is never to operate if the same results can be obtained within a reasonable time by alveolar absorption, but where an operation is necessary the object of an alveolcctomy is so to shape the bone that it will form the best possible painless base to support a denture. Removal of Bo.ve Nodules The commonest variation of the above technique occurs when dealing with small nodules of bone. It is often impossible to remove these nodules with nibblcrs which tend to slip over the hard, convex surfaces without sufficient grip to cut; when this does occur recourse must be had to a bone-cutting bur. The nodules are also very easily removed by a hammer and sharp chisel - a suitable method when operating under a general anaesthetic. Undercut Areas When these are too deep to permit the entry of a denture they should generally be removed or reduced, and the only guidance is the judgment of the operator as to whether retention of the denture -will be satisfactory if the undercut is left and the periphery of the denture adjusted to permit its insertion. The most common positions requiring surgical interference are the oO CLINICAL DENTAL PROSTHETICS maxillary- tuberosities and the lower incisor region, either lingually, Iabially, or both. Over-prominent Maxillary Tuberosities The operation for eliminating an undercut in the region of the maxillary tuberosities in no way differs from other forms of alveolectomy, except in the first incision which is best made in the form of a semicircle extending along the alveolar crest below the bone to be removed and sweeping mesfaliy to it, up to the required height in the sulcus (see fig. 72). Ho. 72 - Alveolectomy of the tuberosity. The line of the incision. An incision of this shape will make the reflection of the muco- periostcum considerably easier, and in cases where it is only necessary to remove a little bone it will obviate the necessity of stitching as the small semicircular flap will be held in place by the pressure of the cheek. If the removal of much bone is contemplated it is wise to X-ray the cases pre-operatively to ascertain the size and proximity of the maxillary antrum. SIMPLE SURGICAL PREPARATION OF MOUTH 87 Interfering Fraena Fraenai attachments rarely require excision as it is nearly always possible to design the denture to accommodate them, but cases do occur where, unless removed, they make the satisfactory wearing of a denture impossible. The operation of fraenectomy is a simple one, the denture being used to keep the cut surfaces apart and so prevent their re-uniting. The impression, from which the denture is con- structed, must be taken in an easy flowing material such as plaster of Paris so that the position of the easily displaced fraenum is accurately recorded. When the denture is ready for processing the fraenai attachment on the model is cut away and the sulcus trimmed to the desired depth, the flange of the denture is waxed into this sulcus, and the denture processed [set fig. 73). (5) (b) Fig. 73 (n) Coronal section through the buccal fraenum on the plaster model. Dotted line indicates the depth to which the model is trimmed. (ft) Side s lew of the fraenum showing the depth to v hich the model is trimmed. Technique of Fraenectomy The operation consists of anaesthetizing and then excising the fraenum with scalpel or scissors to the same depth as was previously done on the model. As soon as the bleeding is checked, the denture is inserted and the patient instructed that it must not be removed, except for cleaning, until the cut surfaces have completely epithelialized over. The patient should be seen occasionally during this period so that any 88 CLINICAL DENTAL PROSTHETICS soreness arising from the wearing of the new denture can be speedily dealt with, as under no conditions may it be left out for more than a few minutes at a time. Denture Hyperplasia These benign overgrowths of mucous membrane arc usually associated with old dentures where alveolar absorption has resulted in settling of the denture leading to chronic irritation of the sulci from the now over-extending denture flange. These hyperplasias are often multiple, one flap ha\ ing grown and then become enclosed under the denture either because of the looseness of fit or because the patient finds it more comfortable in this position. A second flap forms and is in turn enclosed, and so on until in some cases there are six or eight of these overgrowths like leases of a book { see figs. 74 and 52). If the irritation, caused by the over-extended periphery of the denture, is removed, this hyperplastic tissue will slowly be absorbed. The absorption may be complete or partial and if complete no other treatment is required, but frequently these hyperplasias require surgical removal especially if they are of long standing. The operation is a simple one, the flaps of fibrous soft tissue being cut off at their base by a scalpel or scissors, but the removal should be somewhat conservative since a radical removal will leave a much wider wound which, when sutured, wall tend to reduce the sulcus depth considerably. Where the wound is a small one it can usually quite satisfactorily be left to epithelialize over, but if there is a persistent slight haemorrhage which cannot be controlled by the application of hot saline solution the edges must be gently drawn together by one or two sutures. Flabby, Fibrous Ridges A condition is quite frequently encountered where an alveolar ridge which appears normal is found on palpation to lack bony support and to be readily displaceable on pressure. The cause is usually over-stimulation of the alveolar ridge, often from lateral pressure, which has resulted in its excessive absorption whilst at the same time the mucous membrane has become thickened and fibrous {see Chapter II). 9° CLINICAL DENTAL PROSTHETICS It is rarely necessary or even desirable to remove this fibrous tissue as in most cases a flabby ridge is better than no ridge at all, and by using special techniques satisfactory dentures can usually be constructed. WTien, however, it is decided to operate the treatment should be as conservative as possible, the mini- mum amount necessary being removed. The position where it is commonly necessary' to remove fibrous tissue is around the maxillary’ tuberosities, w here it may be so close to the mandible when the latter is in its normal rest position that satisfactory’ dentures cannot be made until some of the fibrous tissue has been removed. The technique of the operation is firstly to remove a V shaped wedge from the centre of the ridge. The mucous membrane on cither side of the area occupied by the wedge is then undermined by the removal of the fibrous tissue. Finally the flaps of mucous mem- brane so formed are approximated by sutures (see fig. 75). Large Torus, Maxillary or Mandibular There is usually a raised, bony ridge running down the centre of the hard palate from the anterior palatine foramen to the posterior border, or any part of this distance, which is known as the torus palatinus. Sometimes this ridge is very' pronounced and covered with only a thin layer of mucous membrane (see fig. 76). There may be two eminences on the lingual aspect of the mandible, one on cither side of the mid-line and usually in the premolar region, each of which is called a torus mandibularis. These conditions do not inconvenience the patient until he is obliged to wear dentures, when pressure may cause con- siderable pain. The correct treatment for these cases, unless they are very' pronounced, is to leave them alone and to relieve the dentures so that under no conditions can they exert any pressure on the torus. If it is decided to reduce them surgically it will be found after reflection of the mucous membrane that they present a hard, smooth, cortical layer of bone which it is almost im- possible to remove with nibblers. A bone-cutting bur or Fig. 75. — Technique of reducing a fibrous tuberosity ! (a) The bulbous tuberosity. (a) A V-shaped section removed and the tissue remaining undermined, (c) The undermined tissues sutured together. hammer and chisel is the best instrument to use, followed by the usual bone-files. It should be stressed that the genial tubercles, which lie immediately on either side of the mid-line on the lingual side of the mandible, must not be mistaken for the torus mandi- bularis. When there has been considerable absorption of the mandible the genial tubercles stand up prominently above the 92 CLINICAL DENTAL PROSTHETICS Fic. 76 - Illustrating a pronounced torus palatinus and the incision made if U is intended to reduce it surgically. general level and arc a considerable handicap to the pros- thetist, but on no account may they be removrd since the genioglossus muscle is attached to them {see fig. 77). Fig. 77. - A prominent attachment of the genioglossus muscle. 93 SIMPLE SURGICAL PREPARATION* OF MOUTH Difficulties Since there are no large blood vessels in the mucous membrane covering the alveolar processes, serious haemorrhage will not be encountered but capillary bleeding or the cutting of a small vessel may sometimes be troublesome: both may be easily controlled. For capillary oozing the application under pressure of gauze soaked in hot (i2o°F.) saline solution is all that is required, whilst small blood vessels may be crushed with tweezers or Spencer-Wells forceps. The application of Oxycel in cases of persistent oozing after suturing is complete usually stops the bleeding. When operating under a general anaesthetic it ma\ still be advisable to inject a local anaesthetic at the site of operation because of its properties of vasoconstriction. The anaesthetist should be consulted before this is done as the effect of the adrenaline on the heart of a patient under a general anaesthetic is variable. Swelling may be controlled by the intra- or extra-oral application of ice packs, whilst haematomata and bruising, though often alarming to the patient, are usually better left alone and disappear quite rapidly. Sepsis, though rare, will usually yield rapidly to correct antibiotic treatment. More extensive operations such as those for bilateral mandibular resection, epithelial inlays, etc., arc outside the scope of the average dental surgeon and consultation with an oral or a plastic surgeon is necessary. Any description of these more serious operations is out of place in a book of this ■description, but they are excellently dealt with in current surgical literature. Chapter V IMPRESSION TAKING In order that a denture may be correctly designed and the necessary constructional work carried out accurate models of the patient’s mouth are necessary' and various methods by which these may be obtained will be described in this chapter. Whilst all operators agree that the models must be an accurate reproduction of the mouth there is considerable difference of opinion over the interpretation of the word accurate. The base on which the denture will rest is covered with mucous membrane which is compressible or distortablc and the shape of this base at rest differs from the shape when resisting the stresses of mastication imposed through the denture which it supports. Further, the denture will be surrounded by moving tissues and the question arises, what position should these tissues occupj' when taking an impression to produce an accurate model? Ideally one wishes to obtain from the impressions, models of those areas of the mouth which will be covered by the dentures, together with the soft tissues which will be in contact with their peripheries during any normal movements made in speech and mastication. Also the model should represent the bearing surface as it wall be when the denture is functioning during mastication, i.e. transmitting pressure. The area which should be included in the impression is frequently far greater than can be used, but it is not possible to design a denture accurately unless the whole area which it could occupy is included in the model, although, for reasons which have been discussed in Chapter II it is not always desirable to finish a denture to this outline. The extent of the impression should be as follows: 9i 95 IStPRESSlOS TAKING The Edentulous Upper From the functional depth of the labial sulcus anteriorly to 2 mm. or 3 mm. beyond the posterior border of the hard palate, as ascertained by palpation. Laterally from the func* tional depth of the buccal sulcus on one side to the functional depth of the sulcus on the other (see fig. 78). The Edentulous Lower From the functional depth of the labial sulcus anteriorly to 2 or 3 mm. above the retromolar pad, posteriorly. From the functional depth of the buccal sulcus to the func- <}6 CLINICAL DENTAL PROSTHETICS tional position of the floor of the mouth laterally, on both sides {see fig. 79). The position of the floor of the mouth depends on the position of the tongue and, as overextension or the denture is apt to cause ulceration of the mucous membrane and instability of the denture, it is desirable to take the impression with the floor of the mouth raised to the functional position, which is obtained posteriorly by protruding the tongue to the extent required to moisten the lips, and anteriorly by raising its tip upwards and backwards. Tic. 79 (a) Coronal, and (4) Sagittal views of the correct extent of a lower impression. The Ideal Impression Material Many materials have been advocated for impression taking and whilst none is perfect each is usually superior to the others in some respect and, in order to have some means of com- parison, it is useful to enumerate the properties which would be possessed by an ideal impression material. IMPRESSION TAKING 97 An idea] impression material would: (1) Be non-injurious to the tissues. Non-poisonous and non-irritant. (2) Be capable of compressing the soft tissues to any desired degree without itself being distorted. This would enable an impression to be taken of the tissues in the position they will occupy under masticatory stresses. (3) Be sufficiently fluid on insertion to give accurate surface detail. Closeness of fit is all important if the full advantages of adhesion and cohesion are to be obtained ( see Chapter I). (4) Be able to reproduce accurately any undercuts which are present. This implies that the material shall be either suffi- ciently elastic to spring out of the undercuts or sufficiently brittle to break easily. If brittle, the material should be capable of easy reassembly. (5) Have a pleasant taste, smell and appearance. (6) Have no dimensional changes cither in or out of the mouth at all normal degrees of temperature and humidity. This is necessary in the interests of accuracy. (7) Set, or harden, at, or near, mouth temperature. If this is not the case then the removal of the im- pression from the mouth without distorting it will be virtually impossible. (8) Have a setting time under the control of the operator. This is required to allow for individual variations of skill and speed. (g) Be capable of having additions made and of reinsertion in the mouth, without distortion. This will allow minor corrections to be made without having to take an entirely new impression. 98 CLINICAL DENTAL PROSTHETICS (io) Have a simple technique. (u) Be compatible with all materials in general use for model making. It is undesirable that the choice of the material for model making should be governed by ihe impression material. (12} Be cheap enough to use once only or capable of easy sterilization if used more than once. Before describing any actual techniques of impression taking there are a few general considerations, common to all, which must first be discussed. The Position of the Patient and Operator For most prosthetic operations the dental chair is set in the upright position, this being specially important during the impression taking since one of the fears existing among patients is that of being choked by the material in use. When the patient is seated the chair should be adjusted so that the head and neck are in line with the trunk (see fig. 80). If the head is allowed to bend backwards from the neck the supra and infrahyoid muscles will be tense and difficulty in swallowing will result, also, should a fragment of impression material break away from the main impression it can more easily fall into the throat and possibly cause obstruction in the airway. Apart from the dangers, the patient’s comfort must be con- sidered if the operator is to receive the full co-opcration required to produce a satisfactory impression. A suitable covering in the form of an apron or large towel should be provided to protect the patient’s clothing and also, ready at hand, a warm, flavoured mouth-wash with which remaining fragments or impression material can be rinsed away on instruction from the operator. The positions of the operator are shown in figs. 81 and 82. Impression Trays Impression trass are used as rigid containers for carrying the impression material into the mouth, for maintaining it in Fia. 8 1 - I (I u< (rating ifx - position of the operator uhm uLin? a. lovirr imprrwion. IC > 2 CLINICAL DENTAL PROSTHETICS position during setting or hardening and supporting it during removal from the mouth and when casting the model. The dental supply houses manufacture a wide selection of impression trays but variations in the sizes and shapes of jaws are such that little hope exists of any one of them fitting an arch contour with the desired accuracy (see fig. 83). Too much space will exist between the tray and the tissue in some regions whilst in others the flanges of the tray will impinge on the ridge or sulcus. To produce a satisfactory impression and avoid variations in transmitted pressure there must be an equal thickness of impression material over the entire fitting surface, also the flanges of the tray must almost reach the functional position of the sulci and fraena and yet not displace them. It is unusual for a stock tray to fulfil these requirements and, there- fore, special trays should be constructed for each patient. The special tray materials vary according to the type of impression technique selected, the more common being: (1) Shellac or a similar"'] proprietary' material (2) Acrylic resin either > (see figs. 84-85). heat or cold cured (3) Tin lead alloy J It will thus be appreciated that for each patient two sets of impressions are usually necessary', the first, the preliminary impressions, taken in stock trays from which models arc cast and the second, the working impressions, taken in the special trays constructed to these models. It is on models cast in the second, or working impressions that the dentures will be constructed. The Preliminary Impression Since this impression will not be used directly in the construc- tion of the denture but only for making a special tray for one individual mouth, the greatest possible accuracy is not required and it is, therefore, possible to select a technique which is simple, quick and which gives the patient the minimum of discomfort. For these reasons composition has been chosen as the impression material, but it must be emphasized that this is {a) Note shortness in lingual pouch and retromolar pad areas. (b) Note poor fit in palate and poor adaptation to ridge*. Fic. 83. -The inaccurate fit of stock trays. IMPRESSION TAKING (e) Tray compound. Fig. 84.-Special trays - Note stepped handles. not a suitable technique for a working impression, though such an impression can be obtained with composition using a special technique as described later in this chapter. Composition, sometimes called impression compound, is the name given to a class of thermoplastic materials containing various waxes, resins and fillers which soften in hot water and harden at or slightly above mouth temperature. Many pro- prietary brands are obtainable with optimum working tem- peratures varying from iio°F. to 140° F. at which tempera- tures they should flow easily. Whichever composition is selected for this primary’ impression the manufacturers’ instructions regarding its working temperature should be strictly observed. Selection of the Stock Tray The alveolar ridges and palate are examined for shape and size, and from a selection of previously sterilized stock trays a suitable upper and lower are chosen and tested in the mouth for their approximation to the oral structures, as follows. fa) Vulcanite. Fie. 85 - Sp<-cial Ti»y*. IMPRESSION TAKING 107 The Upper Trap The tray is inserted in the mouth, the posterior border raised to make contact with the anterior part of the soft palate and it can then easily be seen if the tray will cover the maxillary tuberosities allowing enough room for the impression material. The tray is then slowly raised anteriorly and the lateral flanges watched for clearance of the alveolar ridges and, as the tray is brought right up at the front, the upper lip is lifted so that the labial flange can be checked for fit in this region (rrr fig. 86). The tray must not be pulled forward during examination for buccal and labial clearance. Sufficient space must exist between the tray and the tissues for the impression material and, in some cases, it may be necessary to bend the tray slightly with pliers to provide adequate space and in others to cut and trim the flange to accommodate fraena and CLINICAL DENTAL PROSTHETICS 108 prevent pressure on bony structures such as the zygomatic process of the maxilla. Finally the tray should be checked to make sure that it does not rock from side to side through making contact with the hard palate since, when seated, it should make contact with the crest of the alveolar ridges. The Lower Tray Insert the selected tray in the mouth and pass it backwards until the distal ends coser the retromolar pads, whilst at the same time the patient protrudes the tongue slightly to facilitate placing the tray between it and the lingual surfaces of the ridge. Lift the tray anteriorly and slowly lower again observing its approximation to tire ridge both linguallv, buccally and in front. When satisfied that the selected tray covers the ridge and allows sufficient space for the impression material the flanges are checked for over-extension into the labial, buccal and lingual sulci; the first two visually and the latter by having the patient raise the tip of the tongue to the roof of the mouth. If the tray is not overextended linguallv onh slight finger pressure in the premolar region will be needed to keep it in position. Should the flanges grossly interfere with the fraena or sulci they must be trimmed or another tray selected before the impression is taken. Finally make sure that there is sufficient flange depth in the region of the posterior lingual pouches. Shortness in these areas can be corrected by the addition of a little warmed composition (of a higher softening point than that to be used for the impression), attached to the Fig. 87. - Coronal dumms talen through the and molar region of a lower stork tray showing - (a) A short lingual flange trapping the base of the tongue. (b) The flange extended with compoMtion- (f) The added composition displaced hngually to allow room for the impression material. IMPRESSION TAKING IOg lingual flanges of the dried tray {see fig. 87). Reinsert the cor- rected tray in the mouth and ask the patient to protrude the tongue slightly, this will trim the added composition to the functional depth of the pouches by raising the floor of the mouth and drawing forward the palatoglossus muscles. On removing the tray from the mouth displace the composition lingually to provide space for the impression material and then chill thoroughly. A short tray can be extended distally in the same way, to cover the retro molar pads [see fig. 88). Unless sufficient tray extension exists distally and lingually to push the tongue aside, when the impression is seated there is considerable possibility that this highly muscular structure will be trapped beneath the lingual flanges resulting in an impression which is short in the pouch area. The Order of Impression Taking The trays having been selected and necessary adjustments carried out the next consideration is whether the upper or lower impression should be taken first. From the patient’s point of view the upper impression usually causes the greater *10 CLINICAL DENTAL PROSTHETICS discomfort and anxiety, either through stimulation of the retching reflex or from fear of being choked by the material, but these symptoms are usually absent when taking the lower impression. Some operators prefer to take the more trouble- some impression first assuring the patient that although the upper may be a little unpleasant no such reactions will be experienced with the lower. However, there are some patients who, having felt sick once will do so again even with a lower impression, so it is advocated that in most cases the lower impression should be taken first. A further reason for this is that a foreign body placed in the mouth produces an increase in the rate of salivation and it is, therefore, preferable to have the lower impression seated in position before this takes place. If the upper precedes the lower the operator and the patient may be embarrassed by the accumulation of saliva in the floor of the mouth, the result being a poor impression particularly when using plaster of Paris. The Lower Impression The selected composition is placed in a water bath, preferably thermostatically controlled to maintain the temperature recommended by the makers of that particular brand. After a few minutes the composition is removed from the bath, folded repeatedly from the edges to the centre thus always presenting a smooth surface on one side {see fig. 89), and replaced as quickly as possible to prevent undue loss of heat. This pro- cedure is repeated until the material has acquired a uniform softness throughout. When the composition is ready for use the lower tray is warmed in a Bunsen flame, the composition rapidly dried on gauze, formed into a suitable-sized roll and placed in the tray. It is important to have sufficient bulk extending beyond the flanges so that there is no restriction in flow when pressed into position over the ridge. A trough is indented in the composition with the finger to simulate the ultimate ridge impression ( see fig. 90), and the surface quickly flamed, tempered to avoid burning the patient, by immersing momentarily in the hot water bath and lightly smeared with vaseline. The tray is now placed in the mouth and when the operator is satisfied that it IMPRESSION TAKING ** II j Fig. 89. - Preparing composition to present a smooth surface. ' The thumbs mote away from one another. Ftc. e,o. — Shaping the cnmpoOirn in the tray prior to taking prelim wars impressions. 112 CLINICAL DENTAL PROSTHETICS is in the correct position in relation to the ridge, the patient is instructed to raise and slightly protrude the tongue and as this movement begins the tray is pressed vertically downwards to seat the impression to the desired depth. Pressure in a back- ward direction may also be required to counter the forward thrust from the tongue when protruded. As soon as the impression is seated in position it must be held there quite firmly but without any increase in pressure, in other words the maximum pressure must be exerted when the composition is nearest to the optimum working temperature as the farther it drops below that, the less readily will it flow. The impression obtained so far will reproduce, though not accurately, the denture-bearing surface, but will be over- extended round the periphery and a special tray constructed from it would require considerable time-consuming adjustment before it could be used for taking a working impression. Tins reduction of the special tray can be eliminated, or at least very considerably reduced, if the muscles around the periphery arc brought into play to mould the impression into their functional positions, and this is done as follows: The tray is held firmly in position -whilst the patient pro- trudes the tongue and then moves it from side to side. This movement of the tongue draws forward the palatoglossal arches, raises the floor of the mouth and tenses the lingual fraenum and thus moulds the composition in the lingual sulcus to the raised position of these structures. The buccal sulci and fraena are moulded by manipulating alternate cheeks down- wards and outwards, to free any trapped folds of tissue and then pulling gently upwards, inwards and slightly backwards to obtain the approximate functional position. The impression taking is now completed and all that remains is to hold it lightly but firmly in place for a minute or two, remove, chill thoroughly in cold water and inspect {see fig. 91). Common Faults in Lower Impressions (1) Insufficient depth in the posterior lingual pouch. Causes: (a) Flange of the tray short in this region. (b) Lack of composition in the tray. XI 4 CLINICAL DENTAL PROSTHETICS ( ; very thin flake of plaster left under tongue. (5) Lingual flange of tray correctly inclined fingualfy, a much bulkier piece of plaster left under longue. the tray flange inclined medially the thickness of plaster thus obtained aids the correct union of the broken impression. The tray should now be seated on the ridge and while it is held in this position, the cheeks and lips should be gently pulled upwards and outwards so that the sulci simulate their functional positions. The edges of the seated tray should be almost in contact with the sulci and fraenae all round during these movements and thus will be 2 to 3 mm. short when the original spacing of the spacer is replaced by plaster when taking the impression. Any overextension present must be corrected by trimming and any gross shortness remedied by the addition of composition. Next the lingual periphery should be checked. This is done by requesting the patient to raise and slightly protrude the tongue and if excessive pressure is required to maintain the tray in place it indicates IMPRESSION TAKING 123 that the tray is over-extended, usually in the premolar or first molar regions, or in that of the palato-glossal arch, and should be corrected by trimming. If any doubt exists regarding its final accuracy some composition may be added to the edge of the lingual flange and the tray replaced in the mouth and the patient instructed to protrude the tongue slightly. If, on removal of the tray, the composition is found to have been swept up on to the lingual side of the flange so that the edge of the flange shows or almost shows, then it may be assumed that the depth of the tray is adequate and the com- position may be removed. If, however, the composition has remained in place and merely shows signs of having been moulded by the tissues it should be gently bent lingually so as to provide space for the plaster, chilled and left in position. The Upper The tray should be placed in the mouth and the position of the back-edge checked. This should extend just on to the soft palate. The position of the junction of the hard and soft palates is usually delineated by the two foviae palatinae but this should be verified by gently palpating for the back-edge of the hard palate with a blunt instrument such as a burnisher, and the tray should be trimmed to this position. Next the front of the tray should be lowered and it should be observed if there is sufficient clearance between the tray flanges and the buccal aspects of the ridge. If not, room must be made by bending the flanges outwards. Finally the cheeks and lips should be pulled gently downwards so that the sulci simulate their functional positions: this enables the periphery of the tray to be adjusted in the same way as was done for the lower. Special attention should be paid to ensure that adequate clearance is provided for the root of the zygoma. The correct trimming and adaptation of special trays is a primary factor in obtaining a good working impression and it cannot be emphasized too forcibly that time spent on this is invariably saved by obtaining a good impression at the first attempt. Plaster of Paris Impressions There are a variety of techniques in common use for taking 124 CLINICAL DENTAL PROSTHETICS plaster impressions. For instance some operators favour the placing of plaster in those areas of the mouth in w hich difficulty is experienced in obtaining an impression, before inserting the tray. Others disagree with this method and rely on manipulat- ing the tray and the tissues so that the plaster flows into the difficult areas without the necessity of having to place it there beforehand. Some operators favour raising the front of the upper tray first and others the back whilst some keep the tray horizontal and raise it evenly. The treatment of the back edge of the upper tray aho varies. Some operators Favour post-damming with soft wax or composition to compress the tissues in this region and nho to prevent the escape of plaster towards the throat. Post- damming is a means of increasing pressure over an area in order, either to control an impression material, or to imprme peripheral seal (see fig. 99). Others fix cotton-wool with sticky wax to the tray to prevent this escape or plaster whilst some prefer to leave the back-edge as it is and trust to their judgment Fie. 99- - An upper tray pew-dammed with 4 jtrip of wax. IMPRESSION TAKING 125 of the volume of plaster required and manipulative skill to prevent an excess of plaster escaping posteriorly. The technique described below has been developed over many years and is designed for teaching students to obtain satisfactory plaster impressions before they have gained the manipulative skill which comes with experience. The Loiter Working Impression When the mixed plaster is beginning to thicken slightly the lower tray is filled by means of a spatula, spreading the plaster evenly over the tray surface so that it tends to form a trough for the ridge. If the tray is loaded too soon the plaster being liquid will merely' run out. By r the time the tray' has been filled the plaster in the mixing bowl will have thickened sufficiently to support its own weight. This may be tested by picking some plaster up on the spatula and turning it upside down so that the plaster hangs; it should 12 4 CLINICAL DENTAL PROSTHETICS plaster impressions. For instance some operators favour the placing of plaster in those areas of the mouth in which difficulty is experienced in obtaining an impression, before inserting the tray. Others disagree with this method and rely on manipulat- ing the tray and the tissues so that the plaster flows into the difficult areas without the necessity of having to place it there beforehand. Some operators favour raising the front of the upper Hay first and others the back whilst some keep the tray horizontal and raise it evenly. The treatment of the back edge of the upper tray alto varies. Some operators Favour post-damming with soft wax or composition to compress the tissues in this region and also to prevent the escape of plaster towards the throat. Post- damming is a means of increasing pressure over an area in order, either to control an impression material, or to improve peripheral seal {ste fig. 99). Others fix cotton-wool with sticky wax to the tray to prevent this escape of plaster whilst some prefer to leave the back-edge as it is and trust to their judgment IMPRESSION TAKING I25 of the volume of plaster required and manipulative skill to prevent an excess of plaster escaping posteriorly. The technique described below lias been developed over many years and is designed for teaching students to obtain satisfactory plaster impressions before they have gained the manipulative skill which comes with experience. The Loner Working Impression When the mixed plaster is beginning to thicken slightly the lower tray is filled by means of a spatula, spreading the plaster evenly over the tray surface so that it tends to form a trough for the ridge. If the tray is loaded too soon the plaster being liquid will merely run out. By the time the tray has been filled the plaster in the mixing bowl will have thickened sufficiently to support its own weight. This may be tested by picking some plaster up on the spatula and turning it upside down so that the plaster hangs; it should 126 CLINICAL DENTAL PROSTHETICS just fail to fall off the spatula. At this stage, and not before, is the time to start placing it in the mouth. If it is introduced into the mouth prematurely it will be too liquid to remain where it is placed. A generous portion of plaster should be picked up on the spatula. The forefinger of the left hand should then be inserted into the left lingual sulcus as far back and as deeply as it will go and the tongue gently but forcefully pushed towards the centre of the mouth and held there while the plaster on the spatula is placed deep into the pouch under the mylohyoid ridge (see fig. too). As the spatula is withdrawn the tongue should be allowed to resume its normal position thus covering the plaster and holding it in place. The opposite side is dealt with in a similar manner. Next the lower lip should be pulled gently forward and some plaster placed between it and the ridge, and while the lip is held well forwards the previously filled tray should be rotated into the mouth (see fig. 101) and centred over the ridge and then with a \cry definite wriggling or puddling movement it should be pushed downwards and slightly backwards until fully IMPRESSION TAKING 127 in place. As the tray is wriggled downwards the patient should be instructed to raise the tongue, this will prevent the edges of the tongue or folds in the floor of the mouth being caught under the lingual flanges of the tray. When the tray is fully in place the periphery of the impression must be trimmed. For the lingual trimming the patient is instructed to protrude and raise the tongue slightly and move it gently from side to side. Protrusion and sideways movement of the tongue draws the palato-glossal arches for- wards and raises the floor of the mouth. The elevation of the tongue tenses the lingual fraenum. The plaster lying in con- tact with these structures is, therefore, moulded by these movements so that the impression indicates them in the positions they assume when the tongue is functioning and thus prevents the lingual flange of the ultimate denture being overextended, and so impinging on these structures during tongue movement. Buccal peripheral trimming is effected by, firstly, pulling the cheek outwards and downwards in order to release any air or folds of soft tissue trapped under the periphery. The second movement is upwards, inwards and slightly backwards thus raising the sulcus to the adjudged functional level and so moulding the plaster in contact with it. Finally the labial trimming is effected by drawing the lip upwards and back- wards thus conforming the plaster to the functional position occupied by the labial sulcus and indicating the fraenum. It will be found impossible to perform correct labial trimming unless the tray has a stepped handle (see figs. 84 and 85). Once the peripheral trimming is complete all that requires to be done is to instruct the patient to relax and for the operator to maintain the trav in position and support the jaw until the plaster has set. The tray may be held in position by one of several ways. (a) The tips of the forefingers of each hand may be placed on the top of the tray in the premolar region with the thumbs below the inferior border of the mandible, thus supporting the jaw (see fig. 102). 128 CLINICAL DENTAL PROSTHETICS (b) The first and second fingers of one hand may be placed V on the top of the tray, one on cither side in the prcmolar region, with the handle protruding between them and with the thumb under the chin supporting the mandible (see fig. 103). M The mouth may be completely closed and the thumb and forefinger of one hand encircle the lower part of the face pressing the cheeks and lips on to the tray with sufficient pressure to hold it in place. Hie remaining fingers of the hand support the mandible from below (see fig. 104). In no circumstances must the tray be held in place by mere downward pressure on an unsupported jaw as this is most tiring for the patient. * Durinf Ih/taTtliat the tray is held in the mouth the plaster in the mixing bowl is periodically •—*£“**£ of set, by breaking pieces between the lingers. tVhen it Irac Fig. 103. - A method of holding a lower plaster impression jn place. The thumb is under the chin. turcs with a clean break the impression is ready for removal from the mouth. Before commencing removal the patient should be informed that it may break and that if it does, the broken pieces must be retrieved before rinsing can be allowed. Removal of the impression is commenced by lifting the lips and cheeks away from the periphery to release the air seal which may have developed. A gentle upward movement applied to the handle of the tray will he sufficient to lift the impression from the ridge provided no gross undercuts exist. If undercuts are present, however, a sudden jerk may be required to fracture the plaster. When the tray is fully raised from the ridges it may be rotated out of the mouth (seehg. 101) when it should immediately be inspected to sec if any pieces of plaster have fractured and remained in the mouth; if so, they should be carefully removed with tweezers. The removal of pieces remaining in a posterior lingual pouch is facilitated if the patient places the tip of the tongue into the opposite check. This action raises the floor of the pouch and the piece of plaster with it. I 3 ° CLINICAL DENTAL PROSTHETICS Fio. 104 - A method of holding a lower plaster impression in place. The third and fourth fingers arc under the chin. The impression, together with the pieces broken from it, should be placed on a napkin and left to harden and dry slightly. The broken surfaces are then lightly brushed with a camel hair brush and the small pieces fitted into the main impression, so that the fracture line is almost invisible, and secured with a little molten wax on the external surface. The pieces should be handled gently with tweezers as surface detail can easily be rubbed away. If an impression fractures into many small pieces it is usually quicker and more accurate to take another rather than try to piece the first impression together. The completed impression should embrace ihc entire surface which it is intended to cover with the denture. The periphery should be smooth and rounded and the impression surface smooth {see fig. 105). The only faults allowable are air bubbles small enough to be accurately filled with wax. The Upper II 'orking Impression The ridge depression of the trav is filled with plaster, the palate being left free, or at the most covered with a \ cry thin film; this is because plaster will be placed in the palate of the ( 4 ) The upper. Tig. 105. - Completed plaster impressions. *32 CLINICAL DENTAL PROSTHETICS, IMPRESSION TAKING 133 mouth to obviate air being trapped there. If much is also put on the palate of the tray an excess will be present which will flow towards the throat and cause retching. When the plaster in the mixing bowl has reached the correct consistency for placing in the mouth, as described for the lower impression, some of it should be placed in the buccal and labial sulci and in the centre of the hard palate (see fig. 106). When placing plaster round the tuberosity the patient should be told not to open the mouth too widely, for the reason that the coronoid process is immediately lateral to the maxillary tuberosities when the mouth is fully open, and this will make it difficult to place the loose plaster in position in some patients. The tray is then rotated into the mouth (see fig. 107 ( for a functionally trimmed lower impression. .Vote form of handle. FlO. in. - Tosition of Sulci. Continuous line illustrates their relaxed position; Dotted line their approximate functional position. Towards the back of the mouth the contraction of the buccinator and masseter muscles almost completely obliterates the sulcus. This is because the former muscle crosses the ridge to gain its attachment to the pterygo> mandibular ligamrnt {see fig. 112). (2) With a revolving carborundum stone in the dental engine trim the buccal periphery of the tray so that it is about 2 mm. short of the position occupied by the buccal sulcus in function {see fig. 113). (3) Examine the position occupied by the labial sulcus in function by gently pulling up the Up and trim the tray just short of this position. J46 CLINICAL DENTAL PROSTHETICS Fic. 1 1 2. - Diagram illustrating how ihe buccinator muscle crosses the alveolar ridge at the back or the mouth to gain its insertion into the ptny go-mandibular ligament. Fig. 1 13. - Correctly trimmed tray 2 mm. short of the functional positions 01 the sulci. {$ Trim rive dvstolmgusl aspect, of rive special tray so that it is just short of the position occupied by the palato- glossus muscle when the tongue is protruded to touch the Ups (see fig. rt4). This is most easily accomplished by plac- ing the tray in position in the mouth, then placing the Unger in the posterior lingual pouch over the tray; ash the IMPRESSION’ TAKING I47 patient to protrude the tongue and it can be felt if the palatoglossus muscle comes into contact with the tray. Trim until the muscle just fails to reach the tray. Fic. 1 14 -The llnct curved line represents the position of the ptlato-glossal arch when the tongue (shown by dotted line) is protruded. The tray as illustrated is correctly trimmed and the position of the palpating finger shown. (5) To examine the functional position of the floor of the mouth ask the patient to place the tip of the tongue in the superior buccal sulcus opposite the side it is wished to examine. In the majority of cases the whole floor of the mouth will rise up and overlap the ridge and it will appear as if no lingual sulcus exists; this appearance, how ever, is usually false. The structures in the floor of the mouth immediately under the mucous membrane consist, for the most part, of the sublingual salivary gland, from about the ist molar region forwards, and the deep part of the submandibular salivary gland further back. As these glands are pulled upwards by the action of the tongue they overlap the ridge and mask the sulcus ( see fig. 1 15). The most satisfactory way to trim the tray to the functional position of the lingual sulcus is to place the finger on top of the tray in the area under examination, and ask the patient to repeat the tongue movement. If the tray is too deep the lingual tissues will exert an upward pressure, the degree of which can be judged by the force required to keep the tray in contact with the 148 CLINICAL DENTAL PROSTHETICS lie. 1 15 - Illustrating how the structures or the floor of the mouth rise and overlap the ridge when the tongue is raised. alveolar ridge. Trimming should be continued until only the slightest finger pressure is needed to hold the tray in position. A little practice is needed to gain this sense of touch trimming, but by running the finger along the top of the tray while the patient keeps the tongue elevated, it will soon be learnt where adjustment is required. Final test for stability should be made by holding the tray lightly with the index fingers in the premolar region on both sides and asking the patient to moisten the lips and then place the tip of the tongue in each upper molar region in tum. (6) Tom the tray posteriorly so that it crosses the middle of the retromolar pads. This is very important because the excellent retention exhibited by the final denture cannot be obtained without a perfect peripheral seal being effected in the retromolar area, and this can only be attained on compressible tissue. (7) Trim the tray so that it is clear of the fraenum of the tongue both when it is protruded and -when the tip of the tongue is in contact with the junction of the hard and soft palates. The correct trimming of the tray is essential to the success of this type of impression. When the tray has been satisfactorily trimmed the next procedure is accurately to adapt the entire IMPRESSION TAKING I49 periphery to the functional positions of the various sulci; this is done by tracing on to the periphery' of the tray a low fusing composition and while this is soft placing the tray in the mouth. Tliis softened composition is then moulded by the movement of the various suld and adapts itself closely to their functional positions. The Technique of Adapting the Periphery Apparatus required. Bunsen burner. Pin-point flame. Bowl of water temperature 120° F. Bowl of cold water. Tracing stick (this is a pencil-shaped stick, of special compo- sition which softens at a temperature of iio°-i2o°F. It is usually coloured to differentiate it from ordinary impression composition). (1) Soften the end of the tracing stick in the Bunsen flame. Commencing at the distal aspect of the left buccal periphery, ‘paint’ the trimmed tray with the softened tracing stick for a distance of about 3 cm. The softened composition will adhere to the periphery of the tray {see %• 1 >6)- The procedure of ‘painting’, or sticking the special composition to the periphery' of the tray, is termed tracing. (2) Brush the traced composition with the pin-point flame to re-soften it, as it will have commenced to harden while it was being traced, plunge it into the bowl of hot water and quickly place the tray in the mouth. It is most important to remember that whenever composition is heated with a flame it must always be immersed for a few seconds in hot water to equalize the temperature, otherwise the patient’s mouth may be seriously burned. Using one hand to hold the tray in place and support the jaw, mould the softened periphery to the correct level by carrying out functional mo\ ements of the cheek with the other hand, or by asking the patient to suck the cheeks gently inwards. This operation will adapt the composition into close intimacy with that part of the buccal sulcus adjacent to it. 15° CLINICAL DENTAL PROSTHETICS Fig. 1 16. - Tracing the periphery of an acrylic tray with low fusing tiacing compound. (3) Remove the tray from the mouth, place it in the bowl of cold water, and leave it there for a few moments to chill. Remove the tray from the water to examine the compo- sition which, if correctly adapted, should show a smooth, matt rolled everted edge ( see fig. 117 (a)). If it does not appear everted, or looks rough or is shiny instead of matt there was not sufficient composition present to fill the sulcus in its functional position (see figs. 117 (b) and 1 18). To correct this error, dry the original composition with gauze and add to it by tracing on another layer and rc-adapt to the sulcus. If the tray has not been trimmed sufficiently short of the functional position of the sulcus the composition will be everted completely and the edge of the tray will show through (see fig. 119). In this case the tray must be trimmed further. IMPRESSION TAKING I 5 I Fic. U7. — Section through lower tray showing traced periphery fa) Composition smooth, rolled and everted. ( 4 ) Composition rough and not everted. Fic. 1 18. - Illustrating how the error shown in 1 17 (A) occurs. Tic. tig. Tray overextended, composition completely everted. (4) Adapt the whole of the buccal and labial periphery, working in sections of about 3 cm. at a time. Pay particular attention to the adaptation around the fraenal attachments. {5) When the buccal and labial tracing is complete, commence the lingual tracing, starting with the distal border adjacent to the left palatoglossal muscle. Trace on the composition, flame, dip in hot water and place the tray in the mouth taking care not to brush ofF the composition 152 CLINICAL DENTAL PROSTHETICS against the side of the tongue, as the tray goes into place. Hold the tray in place with the fingers in each premolar region at the same time asking the patient to place the tip of the tongue in the right superior buccal sulcus and then protrude the tongue. These actions pull forward the palatoglossal arch and conform the composition to its correct shape. The position of the tongue in the former of these movements is one commonly assumed during meals, as the tip of the tongue frequently traverses the superior buccal sulcus to clear it of accumulated food. (6) Continue the lingual tracing, section by section, trimming with the tip of the tongue in the buccal sulcus because in addition to pulling the palatoglossal muscle forwards this action also raises the floor of the mouth on the side opposite to the tip of the tongue. The lateral aspect of a correctly trimmed lingual periphery is shown in fig. 120. The notch discernible in IMPRESSION TAKING 153 the region of the second molar is made by the mylohyoid muscle which, in this region, is just a thin slip merging with the posterior aspect of the mylohyoid ridge. The most satisfactory way to trim the lingual periphery is to work forward from the left palatoglossal muscle to the region of the left canine; then forward from the right palatoglossal muscle to the right canine, leaving the area of the lingual fraenum to be trimmed last. (7) When adapting the antero-lingual periphery, instruct the patient first to protrude the tongue and then roll it back and touch the junction of the hard and soft palate with its tip. (8) The final areas to be adapted are over the retromolar pads. Trace both these areas together by dropping compo- sition into the fitting surface, and then place the tray in die mouth and hold it with a firm pressure for about 30 seconds. If the tracing of the entire periphery has been carried out correctly the tray should resist removal and come away with a definite sucking sound. Retention Tests Tests for retention and methods of correcting faults are as follows: (1) Protrude the tongue. The tray should remain in place but if it lifts soften the tracing in the palatoglossal areas and readapt. (2) Place the tongue successively in each superior buccal sulcus. The tray should remain in place but if it lifts, the lingual extension is too deep. Soften the tracing on the side which lifts and readapt. (3) Roll the tongue back to touch the junction of the hard and soft palates. The tray should remain in place but if it lifts the lingual extension anteriorly is too deep, and should be softened and readapted. (4) Open the mouth to the fullest extent. If the tray lifts, soften and readapt the buccal and labial peripheries. (5) Grasp the handle and exert a vertical upward pull. *5 3 CLINICAL DENTAL PROSTHETICS against the side of the tongue, as the tray goes into place. Hold the tray in place with the fingers in each premolar region at the same time asking the patient to place the tip of the tongue in the right superior buccal sulcus and then protrude the tongue. These actions pull forward the palatoglossal arch and conform the composition to its correct shape. The position of the tongue in the former of these movements is one commonly assumed during meals, as the tip of the tongue frequently traverses the superior buccal sulcus to dear it of accumulated food. (6) Continue the lingual tracing, section by section, trimming with the tip of the tongue in the buccal sulcus because in addition to pulling the palatoglossal muscle forwards this action also raises the floor of the mouth on the side opposite to the tip of the tongue. The lateral aspect of a correctly trimmed lingual periphery is shown in fig. iso. The notch discernible in IMPRESSION TAKING I53 the region of the second molar is made by the mylohyoid muscle which, in this region, is just a thin slip merging with the posterior aspect of the mylohyoid ridge. The most satisfactory way to trim the lingual periphery is to work forward from the left palatoglossal muscle to the region of the left canine; then forward from the right palatoglossal muscle to the right canine, leaving the area of the lingual fraenum to be trimmed last. (7) When adapting the antero-lingual periphery, instruct the patient first to protrude the tongue and then roll it back and touch the junction of the hard and soft palate with its tip. (8) The final areas to be adapted are over the retromolar pads. Trace both these areas together by dropping compo- sition into the fitting surface, and then place the tray in the mouth and hold it with a firm pressure for about 30 seconds. If the tracing of the entire periphery has been carried out correctly the tray should resist removal and come away with a definite sucking sound. Retention Tests Tests for retention and methods of correcting faults are as follows: (1) Protrude the tongue. The tray should remain in place but if it lifts soften the tracing in the palatoglossal areas and readapt. (2) Place the tongue successively in eacli superior buccal sulcus. The tray should remain in place but if it lifts, the lingual extension is too deep. Soften the tracing on the side which lifts and readapt. (3) Roll the tongue back to touch the junction of the hard and soft palates. The tray should remain in place but if it lifts the lingual extension anteriorly is too deep, and should be softened and readapted. (4) Open the mouth to the fullest extent. If the tray lifts, soften and readapt the buccal and labial peripheries. (5) Grasp the handle and exert a vertical upward pull. ^54 CLINICAL DENTAL PROSTHETICS Resistance should be felt but if the tray comes away easily tracing stick should be added to the lingual periphery in the premolar regions and readapted. (6) Exert forward pressure on the distal aspect of the handle. The tray should resist and only come free with a sucking sound. If there is no resistance add composition over the retromolar areas and recompress. Completing the Impression Having carefully adapted the periphery, there still remains to be obtained the impression of the bearing surface of the ridge. This is most satisfactorily done by using an impression paste. Spread a thin layer over the dry tray, place the tray in the mouth and seat firmly. Instruct the patient to repeat all the tongue movements made during the peripheral trimming, to trim the buccal and labial peripheries. Hold the tray in place for four minutes and then ask the patient to rinse his mouth with cold water several times. Remove the impression and place in a bowl of cold water, fitting surface upwards, supported by a submerged gauze square to prevent its edges being spoiled by contact with the bowl. Examine the periphery of the completed impression {see fig. 12 1 ), It may be found that areas of the periphery’ show the composition tracing free of paste, while in other areas the paste has covered the composition and corrected the slight inaccuracies of adaptation. The surface of the paste impression should appear smooth and accurately duplicate the surface details. Faults in a paste impression are easily corrected by drying the inaccurate area, spreading over it a thin layer of freshly mixed paste, and re-seating. The completed impression may be placed in the mouth and tested, it should be practically impossible for the patient to dislodge it by any of the usual movements of the tongue, cheeks or lips. Casting the Impression In casting the impression the plaster is brought up the external surfaces of the flanges to a height of approximately 3 mm. in order that the peripheral contour, including its actual thickness, IMPRESSION TAKING CLINICAL DENTAL PROSTHETICS I5b (t>) FlC. 122 (a) Waster model cast w ith impression in place. (b) Plaster mode| after impression has been removed. Note how the peripheries of the impression have been re- produced on the model. is suitably recorded and finally reproduced in the finished denture ( see fig. 122). A similar technique can be used for taking an upper impres- sion (see fig. 123), but this must be post-dammed along the palatal border. The technique lo r post-damming is to add a tracing of composition along the fitting surface of the posterior palatal border, joining the buccal tracings round the tuber- osities. This composition is then softened in the usual way, and the impression inserted and held firmly in place. The patient is instructed to swallow several times in order to mould the tracing in the hamular notches to its functional position. The Cosfposrno.v Impression Compression Impression There are often considerable differences in density and thickness of the mucous membrane in different parts of the denture-bearing area, usually, though by no means always, more marked in the upper than in the lower. The following technique, which has been described by many writers, each 156 CLINICAL DENTAL PROSTHETICS (b) fiq. lai (a) Hatter model cast with imprrwon in place. (fr) Plaster mode! after impression lias been remos ed. Note boss the peripheries of the impression have been re- produced on the model. is suitably recorded and finally reproduced in the finished denture (see fig. 122). A similar technique can be used for taking an upper impres- sion ( see fig. 123), but this must be post-dammed along the palatal border. The technique for post-damming is to add a tracing of composition along the fitting surface of the posterior palatal border, joining the buccal tracings round the tuber- osities. This composition is then softened in the usual way, and the impression inserted and held firmly in place. The patient is instructed to swallow several times in order to mould the tracing in the hamular notches to its functional position. The Composition Impression Compression Impression There are often considerable differences in density and thickness of the mucous membrane in different parts or the denture-bearing area, usually, though by no means always, more marked in the upper than in the lower. The following technique, which has been described by many writers, each IMPRESSION TAKING J 57 158 CLINICAL DENTAL PROSTHETICS with slight variations, is designed to take an impression of these tissues under pressure so that, under the stresses of mastication, the pressure transmitted through the entire mucosa on to the underlying bone is approximately equal over its whole surface. Unfortunately this ideal can never be attained since pressure can only be evenly transmitted to the bone when all the mucous membrane is fully compressed and this state may not be achieved by the operator when taking the impression. Further, masticatory stress is very variable which will result in variable compressibility of the mucosa and uneven pressure on the supporting bone. Nevertheless this type or impression results in a denture which is extremely stable, requires no relieving and since the periphery is functionally adapted it possesses excellent retention. Composition, with its high viscosity, is the only material which is suitable for this technique and by varying its degree of softness, and thereby its rate of flow, the amount of corn- pression obtainable can be controlled within reasonable limits. A composition impression which has been thoroughly chilled, its surface heated and the impression reseated can exert far greater compression than one in which the composition is equally softened throughout its entire mass. A criticism levelled at this type of impression is that sometimes rapid absorption of the ridges with consequent flabbiness of the mucosa results from the extremely tight fit of a denture made to such an impression. A composition should be selected which softens at a temperature between i20°F., and 140° F., flows readily when softened, can be flamed without burning or blistering and which sets hard at mouth temperature. It is a help, and a considerable time saver, to have an electrically heated and thermostatically controlled water bath set at the optimum temperature for the material being used. This is not essential if a thermometer is used constantly to check the temperature of the water which should not be allowed to vary more than 5 0 F. A bowl of iced water to chill the impression will save chairside time but cold tap water can be used equally well except that it takes longer. IMPRESSION TAKING * 59 '< The Special Tray " A special trav is always required for this technique and it should be made in the following way: Cover the whole model with an even thickness of new composition; composition which has been used even once is quite useless for this purpose as many of the more volatile constituents have been lost, thus altering its working proper- ties, raising its softening point, and decreasing its ability to flow. This layer must extend to the full depth of the sulcus all round as it is to be moulded by the soft tissues of the mouth. Next cover the composition with a swaged or cast metal base, so that the composition will be retained in shape when softened (see fig. 124). rio.124. - Detail* of the construction of an upper special tray for taking a compression impression. This stiffener must be left 4 mm. short of the periphery everywhere except at the posterior border; if extended to the periphery it will interfere with the moulding of this area and if it does not support the softened composition at the junction of hard and soft palates, gravity will tend to pull the compo- sition away from the tissues and adequate post-damming cannot be obtained. A handle in the form of a rim, such as is used in bite registration, is convenient, it may be made of old composition and is only really needed anteriorly. The Impression Besides bowls of hot and cold water, a small pin-point flame, cither of gas or a spirit blowpipe, will be required. Only the upper impression will be described as the technique for the lower is similar. l6o CLINICAL DENTAL PROSTHETICS Soften the composition lining of the special tray either by immersing in hot water or by pouring the hot water over it by means of a ladle or syringe; this latter is probably the better technique as theie is then no risk of softening the composition rim used as a handle. As soon as the composition has become soft, it is seated in the mouth with only gentle pressure, and no precautions are taken against distorting the surrounding soft tissues by over-extension, this will be corrected at a later stage. The impression should be held in place until it has hardened, which usually takes about three minutes, it is then withdrawn and immediately placed in the bowl of cold water, being left there until it is thoroughly hard right through. Composition is a very poor thermal conductor and if cold tap w r atcr is being used, it should be chilled for at least as long as was spent in heating; this applies to every occasion when heat is applied. The impression is now dried, the whole surface heated rapidly with a small flame until glossy, dipped for a moment in hot water, seated in the mouth and pressure applied. The reasons for each step mentioned arc as follows: (1) It is dried, as otherwise it will be unevenly heated and softened, i.c. 21 2° F., where wet and much higher else- where. (2) Rapid heating of the surface will leave the remainder of the composition hard so that pressure can be applied without distorting it. (3) Flamed composition, like hot sealing-wax, wall stick and bum and, on removal, will bring the surface tissues with it so that every time a flame is used the impression must be dipped into hot water before being inserted in the mouth (this process is often referred to as ‘tempering’). The pressure in the upper must be directed upwards and backwards towards the crown of the head, and a more evenly balanced pressure is obtained by most operators when pressing with one finger in the centre of the palate, than when using one finger of each hand on either side. This is because right- * handed people unconsciously tend to press harder .with the right hand, and this would make for instability of the denture. IMPRESSION TAKING l6l If both hands are used, however, uneven pressure may be checked by reference to the patient, and if the pressure appeared to him to be less on one side than the other, then the whole of this step must be repeated with greater care. Remove the impression when hard and place at once in cold water; this cooling immediately on removal from the mouth must be carried out throughout the whole technique, as the residual heat in the deeper layers will easily cause distor- tion, even during handling. So far an impression has been obtained which, under an upward and backward load of unknown quantity, will bear equally on hard and soft areas, but which is somewhat over- extended and has no peripheral seal (see fig. 125 (a)). The peripheral borders are now trimmed with a sharp knife until they arc approximately 3 mm. short of the functional position of the sulci and fraena, and the thickness is also reduced to about 3 mm. by removing part of the rolled border in contact with the cheeks and lip (see fig. 125(6)). Particular attention must be paid to this stage of the technique as any composition that impinges on the sulci or fraena will result in the finished denture being dislodged by muscular pull: if retention is good enough to prevent this the consequence will be pain and inflammation at that point. Once this trimming of the impression is completed, the periphery is rebuilt and adapted section by section, using a low-fusing tracing composition in stick form. Begin at the distal end of one buccal border, dry, add tracing composition for 2 cm. to 3 cm., flame, temper, insert and mould for the functional position. Details of trimming for the functional position have already been given in previous techniques, but emphasis must be laid on the fact that some pressure must be maintained to keep the soft composition in contact with the mucous membrane of the ridge so that excess composition will be rolled to the correct position and not pulled away (see fig. 126). Repeat the procedure until the whole periphery from tuberosity to tuberosity has been readapted and after each section has been trimmed, place the impression in cold water until it is thoroughly hard. CLINICAL DENTAL PROSTHETICS IMPRESSION TAKING 163 Fig. 126. - Right side of diagram illustrates the direction in which pressure must be applied to keep the composition in Contact with the tissues when functional tnmming is being carried out. Left side illustrates what occurs if the cheek is merely pulled outwards and downwards. The posterior palatal border still remains to be adapted and this is done as follows: The vibrating line of the soft palate is first located, usually by asking the patient to open his mouth widely and say a prolonged ‘ah’ when the movement of the palate is easily seen. This line may be marked in the mouth with an indelible pencil and the impression cut or added to so that it terminates just anterior to this vibrating line, but posterior to the hard palate. Again dry the impression, add a tracing on the fitting surface just anterior to the palatal border, flame, temper, place in the mouth and hold with a firm pressure. Chill thoroughly after removal. There remain two areas which so far have received no attention, the hamular notches, and it is here that the final seal is produced. Place a tracing in both these areas and, after the usual routine, scat the impression firmly in position and ask the patient to swallow several times which wall trim the soft tissues in these regions. The impression should now be complete {see fig. 127) and it should be impossible for the patient to dislodge it by any normal movement of the lips and cheeks. Tests for Retention (1) Upward and outward pressure in the incisor region. If the impression can be dislodged without great difficulty the posterior border requires further post-damming. (2) Upward and outward pressure in the premolar regions. If the impression Jails, then further peripheral seal is 164 CLINICAL DENTAL PROSTHETICS Fic. 127 - A completed upper compression impression. required on the opposite side, usually around the tuberosity. Sometimes a difficult air leak can be spotted by seeing a small collection of bubbles at one spot on the periphery and this must be corrected in the usual way. (3) Pulling down the upper lip. Overextension in the labial sulcus is common and if this test dislodges the impression the labial periphery must be readapted. At some point during the taking of the impression the air seal will become sufficiently good to make removal of the impression difficult, and this can be overcome by asking the patient to close the lips and blow out the cheeks, thus forcing air under the impression and allowing it to drop. DiJUaiJJus The commonest cause of failure with this technique is impatience on the part of the operator at the time spent in chilling the impression but, unless it is thoroughly hardened after each insertion in the mouth, warp age will occur and the IMPRESSION TAKING 165 only remedy for this warpage is to start the impression over again from the very first step, there are no short cuts. General Remarks on Impression Taking Most of the difficulties encountered in impression taking can be traced to the operator’s lack of attention to details of technique, and especially the acceptance of a poor stock tray impression with the comment that, ‘it will be good enough for making a special tray’. It is of extreme importance that the primary impression should record the entire possible denture- bearing surface but, at the same time, does not encroach on the movable muscular tissues. Special trays must be carefully checked for possible over- extension and, if plaster is the material of choice, it is necessary to ensure that sufficient space exists in all regions, between the fitting surface of the tray and the tissues to be recorded. A suitable thickness of material is necessary so that fractured areas may be accurately reunited. Nausea A disturbing factor experienced by some patients is the sensitivity of the soft palate and the dorsum of the tongue to foreign bodies; such conditions may produce retching and in rare instances actual vomiting. This is a normal reaction to gentle, intermittent stimulation of these parts and many patients arc more affected during the selection of a standard tray than during the actual taking of the impression with its firmer contact over a more restricted area and its avoidance of the dorsum of the tongue. Unfortunately with the more difficult cases there is always a psychological factor present as well, probably connected with a fear of choking, but a success- ful operation can be assured by adopting one or more of the following methods: (1) A firm, sympathetic manner of self-confidence on the operator’s part. (2) Assure the patient that no difficulty will be experienced if instructions arc followed, and that the discomfort will be minimized as much as possible, being in any case only for a short time. l66 CLINICAL DENTAL PROSTHETICS {3) The patient should blow the nose to clear any nasal obstruction and then be encouraged in deep, nasal breathing. (4) Explain to the patient that, as soon as the impression is seated, the head may be brought well forward over the lap and that a bowl will be provided to hold under the chin to catch any saliva that may run out of the mouth. This will reduce the fear of being choked and will also help by keeping the patient’s hands occupied, and any pieces of plaster which do drop from the back edge of the impression will fall on to the front, not the back, of the tongue, and so will be under control as explained in the chapter on applied anatomy. 1 5) Carry out the impression technique using as little material as is commensurate with procuring a satisfactory im- pression. Avoid touching the dorsum of the tongue with the back of the tray and seat the impression as quickly as possible. (6) Desensitize the surface of the mucous membrane with: (a) A phenol mouth-wash of one part phenol to eighty parts of water as cold as can be procured. (£) Sucking a tablet made for this purpose. (c) The application of a surface type of local anaesthetic either in the form of a cream or a spray. As sensitive patients wall experience the same difficulty at each succeeding visit and as the wearing 0/ the finished denture will be difficult, it is advisable to construct a fitting base-plate in acrylic on the first impression and give it to the patient with instructions to practise wearing it for increasingly longer periods each day until it can be worn for at least an hour \\ ithout discomfort. Impression materials vary in their nauseating effects, partly wring to their viscosity and hence their controllability and partly owing to their consistency and flavour. Patients dislike plaster of Paris more than any other material, even when it is flavoured; the alginates are tolerated slightly better; composi- tion is usually tolerated n ell, probably owing to its putty-like consistency and its heat; zinc oxide paste seems to be disliked IMPRESSION TAKING 167 least of any but this may be largely due to its only being used in a tray which already fits, though its flavour of cloves undoubtedly helps in some cases. Impressions for Bedridden Patients Occasionally the prosthetist is called upon to take impressions for a patient who is confined to bed. The first thing to do if possible is to turn the patient round in bed so that his head is at the foot, then the head board of the bed will not obstruct the operator. The use of plaster or hydrocolloid is contra-indicated as these easy-flowing materials are difficult to control, but com- position or zinc oxide paste have a relatively high viscosity and can be more readily controlled. Lengthy techniques cause undue fatigue and should be avoided. Summary of Advantages and Disadvantages of Various Impression Materials In conclusion, it is felt that it may be useful to summarize the advantages and disadvantages of the various impression materials which have been discussed. Plaster of Paris Advantages (а) It produces excellent surface detail. (б) It is dimensionally accurate if used with an anti- expansion solution. (c) It does not distort on removal from the mouth but frac- tures if deep undercuts exist and may be accurately assembled out of the mouth. (tf) The rate of set is under the control of the operator. (e) It is compatible with all materials commonly used for making models and is the only material into which metal can be poured. (f) It is hygienic, as fresh plaster must be used for each impression. ( g ) It is cheap. Disadvantages (a) It cannot be used for compressing the tissues. 1 68 CLINICAL DENTAL PROSTHETICS (£) In very wet mouths the surface of the plaster tends to be washed away spoiling the surface detail. (c) It cannot be added to if faulty. (d) Its taste and rough feel when in the mouth induce nausea in some patients. (<) It is disliked by many patients. Indications for Use (a) In all normal mouths when the factors affecting retention are favourable. ( b ) Whenever excessive flabby tissue covers the ridges. Sodium Alginate Advantages [a) It produces excellent surface detail. (A) It is dimensionally accurate if cast within a short time of remoral from the mouth. (c) It is elastic and trill spring over bulbous areas returning to its correct position when removed from the mouth. This only applies if the undercuts are not too deep. (d) It is hygienic, as fresh material must be used for each impression. (f) It does not Jose surface detail in very wet mouths. Disadvantages (a) It cannot be used alone for compressing the tissues. (A) It cannot be added to if faulty. ( c ) Distortion may occur without it being obvious. It must be held stationary in relation to the tissues throughout its setting period and it must remain adherent to the tray during removal. Indications for Use (a) Whenever there are undercuts which are too severe for plaster. (A) In mouths with an excessive flow of saliva. Zinc Oxide and Eugenol Paste Advantages (a) It produces excellent surface detail. (A) It is dimensionally accurate as it is only used in a thin layer. IMPRESSION* TAKING 169 (c) It is hygienic, as fresh material must be used for each impression. (d) It docs not lose surface detail in wet mouths. (<•) It can be added to and readapted if faulty. (/) It can be used for compressing soft tissues. (g) It reduces nausea to a minimum. (A) It adheres well to a dried surface so that when the minimum of material is used there is little degree of flaking on removal from the mouth. Disadvantages (a) It cannot be used when more than a slight undercut exists. (b) Only sets rapidly when in a thin layer and therefore can only be used as a wash material. (r) Will not produce a satisfactory impression of the periphery unless supported by a very accurately adapted tray. (d) Some patients are allergic to cugcnol and in these cases it may cause a chemical burn. Indications for Use (a) As a final wash material when using techniques which have produced a closely adapted periphery. (A) In cases exhibiting pronounced nausea. Composition Advantages (a) It can be used for compressing soft tissues. (A) It can be added to and readapted. (r) It can be used for any technique requiring a close peripheral seal. ( d) It can be used in combination with other materials. Disadvantages (a) It distorts easily and should not be used where excessive undercuts exist. It may also be distorted if any pressure is applied to it out of the mouth before it has been chilled. (A) It does not reproduce fine surface detail. (c) As it can be re-softened and used again it tends to be unhygienic because it cannot be sterilized easily without destroying its properties. 170 CLINICAL DENTAL PROSTHETICS Chapter VI RECORDING THE POSITION OF CENTRIC OCCLUSION From lime immemorial the procedure of recording the relationship of the mandible to the maxilla in the position of occlusion has been termed ‘ taking the bile'. This term is misleading for the relationship which one seeks to record is not that employed in biting or incising. A suitable term for this procedure is ‘ recording the position of occlusion' and therefore throughout this volume this term will be substi- tuted for * taking the bite' and when discussing those pieces of apparatus commonly termed ( bite blocks' the term ‘ record blocks' will be used which is short for blocks employed for recording the position of occlusion. The first stage in the construction of full dentures has been described in the preceding chapter and has resulted in two models which are accurate reproductions of the denture- bearing area of the patient’s mouth. Whilst the natural jaw bear a very definite relation to each other, both at rest and when functioning, the two models do not. It is the purpose of this chapter to explain how the models may be related to each other in the exact manner of their natural counterparts. The Maxillo-mandibular Relations There are three relationships of the mandible to the maxilla: (1) With the teeth in centric occlusion. (2) With the mandible in its rest position when the teeth are always out of contact (relaxed relation). (3) The dynamic relationship of the jaw during function. Centric Occlusion The maxilla is firmly united to the skull and only moves with this structure. The mandible on the other hand is attached to the skull by the two temporo-mandibular joints and is capable 172 RECORDING POSITION OF CENTRIC OCCLUSION of opening, dosing, protrusive, rctrusive and lateral movements, and also combinations of any of these. The mandible is prevented from overdosing by the occlusion of the natural teeth, and it is also necessary to retrude the mandible at the conclusion of all functional movements,- in order that the cusps may interdigitate. These two facts result in the mandible returning, at the con- clusion of every masticatory stroke, to a position in which the cusps of the opposing teeth are in contact, and the heads of the condyles are placed as far back in the glenoid fossae as they can go without sacrificing their ability to make lateral movements. This maxillo-mandibular relation is termed centric occlusion (see fig. 130). Fla. 130. - The centric occlusal position of the jaws. The Relaxed Relation or Rest Position When the mandible is not functioning, and provided the subject is not in a state of tension, and is breathing normally through the nose, the muscles and ligaments which are attached to the mandible support it in a relationship to the maxilla which is remarkably constant for any given individual. Tn this relation the heads of the condyles are fully retruded in the glenoid fossae to the extent that will allow freedom for lateral mm-cments and the occlusal surfaces of the teeth arc separated by 2-4 mm. (see fig. 1 3 1). The term relaxed relation is also commonly used for any relationship of the mandible to the maxilla from this physiological rest position up to but not includ- ing contact of the teeth. a. The relationship of the mandible to the maxilla both vertically and honzontatlv dictated b> the interdigitation of the natural teeth Note head of condole retmded in glenoid fossa. ■ * r. . • f ft-' * i -able has I), Thr fin Mini tJrntiirr* comiruftnl to itw* jaw rrlatn*nJnp jrivrn l>\ ihc rcmfii btork* mtnrr pcrmanctiilv I hr rrUnun- »}<»p of ifjr nunOi!)!r to llir nunlh a. The relationship of the mandible to the maxilla both vertically and horizontally dictated by the interdigitation of the natural teeth. Note head of condyle retrudcd in glenoid fossa. it. The teeth have all been extracted and the mardibtc has no fixed relationship to the maxilla and can wander widely both vertically and horizontally. 1*. The finidted dentures comimcted to the jaw irhlinnibip Kitrn Ij\ the rrmnl htorVi restore permanent!* the reUtii in- »Jnp rf ihr mandiMe to the maxilla. ■78 CLINICAL DENTAL PROSTHETICS RECORDING POSITION OF CENTRIC OCCLUSION 177 which the mandible bore 10 the maxilla when the natural teeth were present and relate the models to each other in a like manner. The teeth may then be set up on the models with the knowledge that they will articulate correctly when placed in the mouth. The Relations Which Require to re Recorded These depend on the type of articulator which is to be employed. Plane line articulators only require centric occlusion, while anatomical articulators require that the paths of the cond)les and their relationship to the mandible be also recorded. The difference between these two types of articulator is that the plane line permits only a hinge movement whilst the anatomical type copies functional movement (n-ffigs. 133, 134'. Tio. 133.- Complete ls not so obvious as it is muffled by the food. 5. Appearance The result of over-opening must be an elongation, of the face, but if it is only slight it will usually pass unnoticed. What u ill, however, generally be obvious, is that at rest the lips arc parted, and that closing them together will produce an expression of strain (see fig. 151). Effects of Excessively Reducing the Vertical Dimension 1. Inefficiency This is due to the fact that the pressure which it is possible to exert with the teeth in contact decreases considerably with over-closure because the muscles of mastication are acting from attachments which have been brought closer together. 2. Cheek Biting In some cases where there is a loss of muscular tone, as well as a reduced vertical height, the flabby cheeks tend to become trapped between the teeth and bitten during mastication. When the over-closure has been deliberate, it is possible to avoid this cheek biting by setting the upper posterior teeth more buccally than normal, thus producing a greater overjet. Also by plumping the buccal flange of the denture the cheek may be given added support (see fig. 152). Fig. 151. -Profile view illustrating effect of alteration of vertical dimension on appearance : fo) Correct dimension. ( 4 ) Closed. (c) Open (note parting of lips). 202 CLINICAL DENTAL PROSTHETICS Fic. 152. — Cheek biting. (a) How it occurs. (A) Illustrating small buccal ovetjet. (c) Increased buccal ovcijet to prevent biting. (d) Plumping buccal flange. (Plumped part is shown in black.) 3. Appearance The general effect of over-closure on facial appearance is of increased age: there is closer approximation of nose to chin, the soft tissues sag and fall in, and the lines on the face are deepened. The greater the degree of over-closure, the more exaggerated arc these effects. 4. Soreness at the Corners of the Mouth (Angular Cheilitis) ( see fig. ■ 53 ) Over closure of the vertical height sometimes results in a falling in of the comers of the mouth beyond the vermilion border and the deep fold thus formed becomes bathed in saliva: this area may become infected and sore and is then difficult to cure whilst it remains moist. Opening the vertical height restores the corners of the mouth to their normal posi- tion, sometimes producing a marked improvement or cure. A deep natural fold cannot be eliminated by this means and in no case must the increased vertical height excede the free way space. 5. Pain in the Temporo-mandibular Joint In cases of gross over-closure of the jaws, pain in the temporo- mandibular joint may occur, probably due to strain of the RECORDING POSITION OF CENTRIC OCCLUSION 203 Fic 153 (a). - Soreness at the cornets of the mouth. Note how the comers of the lips have fallen in. joint and associated ligaments, which may be relieved by restoration of the correct vertical dimension. 6. Cos ten’s Syndrome Costen’s syndrome is stated to be the result of prolonged over-closure, though his explanation of how these symptoms are produced is now doubted. It consists of: (a) Mild catarrhal deafness and dizzy spells which'are relieved by inflation of the eustachian tubes. (i) Tinnitus, or at times a snapping noise in the joint which is experienced while chewing. Painful, limited or excessive movements of the affected joint. 206 CLINICAL DENTAL PROSTHETICS is adjusted to rest on the skin covering the front of the chin. Remove the dakometer and chill the composition. Replace the instrument holding the composition carrier firmly in position, and, whilst the patient maintains centric occlusion, the chin- piece is screwed up by the screw (D) until the indicator on the spring pressure gauge (E) corresponds with the line on the sleeve (F). Take the readings on the vertical scale (G) and on the chin support (C), Finally, adjust and record the vertical and horizontal positions of the incisor attachment (H) by moving it until the ‘L’-shaped terminal engages the incisal edges of the upper centrals. The readings are noted on the patient’s chart and the composition nose-piece preserved for (hat patient, so that the whole instrument can be reassembled when taking the records after he has been rendered edentulous. 2. The Willis' Gauge When this is used for recording the vertical height before extraction, the arm (A) (see fig. 155} is placed in contact with the base of the nose and the arm (B) is moved along the slide Fic 153(6). - Closr up of a chronic angular cheilitis ( c ) Tenderness to palpation over the tcmporo-mandibular joint or dull pains. (. d ) Various neuralgic symptoms such as burning or prickling sensation of the tongue, throat and side of the nose. Various forms of atypical head pain, particularly that referred to the temporal region or the base of the skull. ( e ) Dryness of the mouth due to disturbed salivary gland function. Pre-extraction Records „ In practice the dental surgeon will usually cither extract the teeth and construct dentures, or replace existing dentures; it is not often that patients present themselves for treatment without either natural or artificial teeth. When the dental surgeon is rendering a patient edentulous he has the oppor- tunity for recording the vertical dimension and the position and shape of the teeth before they are extracted. The following methods may be used to obtain this information: RECORDING POSITION OF CENTRIC OCCLUSION 205 I. The Dakometer This instrument records both the vertical dimension with the natural teeth in occlusion and the position of the upper central incisors; in most cases recordings can be obtained with an error range of i i mm. The instrument is used as follows {ste fig. 154): Fjo. 15$. — The Dakometer in position. Press a piece of softened composition into the carrier (A) and, with the instrument in position, mould it into thedepression at the bridge of the nose; the member (B) of the chin piece (C) 206 clinical dental prosthetics is adjusted to rest on the skin covering the front of the chin. Remove the dahometer and chill the composition. Replace the instrument holding the composition carrier firmly in position, and, whilst the patient maintains centric occlusion, the chin- piece is screwed up by the screw (D) until the indicator on the spring pressure gauge (E) corresponds with the line on the sleeve (F). Take the readings on the vertical scale (G) and on the chin support (C). Finally, adjust and record the vertical and horizontal positions of the incisor attachment (H) by moving it until the *L’-shaped terminal engages the incisal edges of the upper centrals. The readings are noted on the patient’s chart and the composition nose-piece preserved for that patient, so that the whole instrument can be reassembled when taking the records after he has been rendered edentulous. 2 . The Willi? Gauge When this is used for recording the vertical height before extraction, the arm (A) (see fig. 155) is placed in contact with the base of the nose and the arm (B) is moved along the slide Fig. 155. — The Willis’ gauge in place on the face. RECORDING POSITION OF CENTRIC OCCLUSION 207 (D) until it is lightly but firmly touching the lower border of the chin, when it is locked in position by the screw (C). The distance on the scale (D) is recorded on the patient’s chart. This is not a very accurate measurement; it depends on the operator always applying exactly the same degree of pressure when the instrument is making contact with the base of the nose and with the undersurface of the chin. 3. Profile Tracing A piece of soft lead ware is moulded to the contour of the face starting on the brow’, following down the nose and lips and ending just below the chin ( see fig. 156). It is then carefully laid on a piece of stout card or thin wood, the outline pencilled in and the profile cut out. This template is then placed on the lace to check its accuracy and to mark the position of the upper central incisors. With the template held in contact with the face, a mark is made which corresponds with the incisive edge of the centrals. A line is drawn from this mark at right angles to the straight edge of the card, and on this line a second mark is made. The distance from the second mark to the labial surface of the central incisor is noted (see fig. 157). Fio, 15G Fio. 157 RECORDING POSITION OF CENTRIC OCCLUSION 2O9 Sometimes it is desirable to record the acquired position instead of the true position, and this is discussed in Chapter III, but it is only the true retruded position which is being considered here. Stress has purposely been laid on the difficulty to be expected in many cases in obtaining a correct retrusive record, because great patience will often be needed as satis- factory dentures cannot be constructed unless the record is correct. There are many aids to help the prosthetist to obtain the retruded position and where one fails another may well succeed, such aids arc: 1. Instructions to the Patient Always ask the patient to ‘close’, never ask him to ‘bite’. ‘Bite’ conveys the impression of incising, and to incise requires some protrusion of the jaw, which is just the reverse of what is required. 2. Tongue Relrusion Ask the patient to place the tip of the tongue as far back on the palate as possible, to keep it there and close the blocks together until they meet (see fig. 158). Some patients have a tendency to let the tongue move forward and it is often helpful RECORDING POSITION OF CENTRIC OCCLUSION 2C<) Sometimes it is desirable to record the acquired position instead of the true position, and this is discussed in Chapter III, but it is only the true retruded position which is being considered here. Stress has purposely been laid on the difficulty to he expected in many eases in obtaining a correct rctrusivc record, because great patience will often be needed as satis- factory dentures cannot be constructed unless the record is correct. There arc many aids to help the prosthetist to obtain the rctruded position and where one fails another may well succeed, such aids arc: l. Instructions to the Patient Always ask the patient to ‘close’, never ask him to ‘bite*. ‘Bite’ conveys the impression ofincisin g, and to incise requires some protrusion of the jaw, which is just the reverse of what is required. 2. Tongue Iielrusion Ask the patient to place the tip of the tongue as far hack on the palate as possible, to keep it there and close the blocks together until they meet (see fig. 15B). Some patients have a tendency to let the tongue mose forward and it is often helpful 212 CLINICAL DENTAL PROSTHETICS tinuously for as long as possible and to finish in a retrusive position with the blocks in contact. The object is to tire the lateral pterygoid muscles so that they will relax when the movement ceases, and so allow the condylar heads to be retruded. 6. Head Position Having lowered the head rest, ask the patient to bend the head backwards as far as possible. This will produce some backward pull on the mandible, but places the patient in a position in which it is difficult for the operator to check the relationship of the blocks. 7. The Temporalis Muscle Check The anterior fibres of the temporalis muscle only contract on closure of the mandible if it is retruded. Thus if the fingers arc placed on the temples and the patient closes the rims firmly the contraction or not of the anterior fibres of the temporalis may be used as an assessment of mandibular retrusion. 8. The Gothic Arch Tracing This may be obtained either by intra-oral or extra-oral methods; both make use of the same principle and result in the most reliable assessment of centric occlusion. The technique shows the horizontal movement of the mandible in the form of a tracing, made by a pointed attachment fitted to one block on a recording plate fitted to the other (srr figs. 161 and 162). Consider for a moment the lateral movements of the mandible. Starting from the retruded position and moving to the right, the left condyle is drawn forwards down the eminentia whilst the right condyle acts as a pivoting point, and vice versa for the left lateral movement. If a tracing be taken from a given point in the mid-line of the mouth, two lines would result which would converge to a sharply pointed apex; if the mandible were then protruded, the tracing would also start and finish at this point, since it indicates the retruded position ( see fig. 163). If this principle is applied, the point at which the tracings intersect and form a sharp, pointed arrow head will be the retruded mandibular position for a given individual. Tic. 162. — Details of extra-oral tracing apparatus, showing tracing stylus attached to the upper block and tracing plate attachetl to the lower block. Tracing Devices and Technique The intra-oral device consists of a carrier through the centre of which is threaded a pointed stylo controlled by a locking nut. After the correct vertical height has been obtained, 214 CLINICAL DENTAL PROSTHETICS Fla 163 . - Illustrating how a gothic arch tracing is made. The arrow indicates the direction of tra\ el of a sr> lus attached to a lower block, tracing on a plate fixed to the tipper block. (a) When the mandible is protruded. (4) When it is mosed to the right. (f) When it is mot cd to the left. Insert shows the form of the completed tracing. the unit is fitted to the lower rim so that the tracing point is placed centrally across a line joining the premolars. The tracing plate is cut from flat sheet metal and inserted parallel to and just below, the occlusal surface of the upper rim (see fig. 16 1). Place the blocks in the mouth with the stylo adjusted to hold the rims slightly apart. The patient now performs lateral jaw movements, keeping the tracing point in contact with the plate the whole time. ^Vhen the operator is satisfied that the patient can perform these movements correctly, the upper block is removed and after the tracing plate has been filmed with black carding wax the block is replaced in the mouth. Lateral and protrusive movements are made, the tracings examined, and if a clearly defined arrow head has been recorded the retruded position has been obtained. Drill a RECORDING POSITION OF CENTRIC OCCLUSION 2IJ Flo. 164. - Upper block uiik completed gothic arch trac- ing and hole bored at apex. Insert shows enlarged new of tracing and hole. small hole through the apex ( see fig. 164) to accommodate the point of the stylo and ask the patient to move the mandible until the point slips into the hole; the blocks should now be in even contact and no longer held apart by the screw. The blocks are united in the mouth with hot wire staples which are inserted as shown in fig. 165, and care must be taken not to burn the patient’s lips. Fic. 165. - Illustrating the method of sealing the bite blocks with hot wire staples. The above description relates to a method of obtaining a gothic arch tracing on conventional record blocks. Such a tracing can be obtained perhaps more simply by fixing the tracing plate and stylo directly to base plates made of cold cure acrylic ( see fig. 166). The technique of using this apparatus is to obtain the vertical jaw separation by screwing the stylo bolt up and down and locking it at the correct height and then performing the tracing as described above. The base plates arc united in the mouth in the retruded relationship by placing plaster of Paris between them which, when set, firmly unites them in the correct relationship (see fig. 1G7). 2l6 CLINICAL DENTAL PROSTHETICS Tic. 167. - Gothic arch apparatus has been united in mouth with plaster of Paris and models articulated. 2l8 CLINICAL DENTAL PROSTHETICS This method gives no indication of the incisal or occlusal planes and centre line and therefore an additional upper base plate is required to which the selected six upper front teeth arc attached in the desired position by wax at the chairsidc. The models are mounted on the articulator by means of the tracing apparatus and then the upper base carrying the front teeth is substituted and the set-up continued by the technician on this, the upper front teeth remaining in place. In some cases several tracings will have to be taken before the typical arrow head or gothic arch is secured; a rounded apex indicates that the condylar heads are not fully retruded {see fig. 168). Fic, 168. - Illustrating various tracings which mav be obtained All indicate that the mandibular condyles are not fully retruded. The extra-oral apparatus is similar to the intra-oral except that the stylo and tracing plate are outside the mouth, being attached to the record blocks by rods which pass between the lips {see fig. 162). This technique is dependent on well-fitting, stablc’ bascs, and those of acrylic undoubtedly give the most uniformly successful results. Methods for Sealing the Record Blocks Together 1. Heat When it is not intended to record more than the retruded position, the blocks can he sealed together in the mouth by means of a hot wax-knife, care being taken that the knife is not hot enough to cause the wax to run. With this method it is sometimes difficult to remove the united blocks from the mouth, but if the patient is asked to open his mouth widely RECORDING POSITION OF CENTRIC OCCLUSION 2 If) and to push the blocks out with his tongue, no difficulty will be encountered. 2. Wax Template A few ‘V’-sliapcd notches or circular pits arc cut in the occlusal surfaces of the rims {see fig. 169) care being taken not to Tie. 169(0). - Illustrating the form of ttie notches amt piu cut In the nmi when recording ccntnc occlusion with a wnx template. 220 CLINICAL DENTAL PROSTHETICS obliterate the centre line marking. The blocks arc placed in the mouth, the lower with a layer of softened pink wax covering its occlusal surface; this layer is usually made up of two thicknesses of pink sheet wax which must be thoroughly softened. The patient is asked to close the blocks together, using whatever ‘aid’ has been found most useful, and as soon as the operator has checked that the rctrusivc position is correct the patient is asked to close more firmly. Plaster of Paris may be substituted for wax (see fig. 170) and is helpful in those cases where the patient tends to slide the jaw forward as they close. The softness and lack of resistance of the plaster, thus reducing the pressure required to close, often inhibits the desire to protrude the jaw. 3. Pinning Some patients tend to protrude the mandible when they have brought the record blocks into occlusion, and if a wax wafer is RECORDING POSITION OF CENTRIC OCCLUSION 2’i used in these cases it acts as a lubricant between the rims and permits this sliding movement. In such cases the blocks may be fixed by means of pins instead of a wax wafer. Old gramophone needles are very useful for this purpose, two being warmed and inserted in each lower premolar area with their points protruding not more than 2 mm. above the occlusal surface [see fig. 171). The lower block is thoroughly chilled to Fig. 171.— Illustrating the position and degree of protrusion of the pins when these are used for recording the position of eenlnc occlusion. Fig. 172. — Coronal section illustrating how rims tiit off the ridge. Premature contact on right leads to tilt on left (arrowed). Fig. i 73. - Premature contact of record blocks at heels. support and retain the pins and the upper rim very slightly softened in the area into which the pins will be forced; the blocks are inserted and closed together, and the pins will prevent the sliding movement unless the upper rim lias been over-softened. Common - Errors in Record Taki.vc Errors in occlusion of the finished dentures frequently arise as a result of errors at the record stage other than an incorrect vertical or antcro-posterior dimension. The commonest of these are: (/>) Tilling of ibe blocks off ibe ridges resulting bom uneven contact ( see fig. 172). (b) Premature contact of the heels of the record blocks leading to displacement or tilting of the blocks ( tee fig 173). (c) Heavy contact of the heels of the plaster models which prevents them being accurately seated in the blocks (see fig. 174}. Fig. 174. - Note contact of the licels of tlie plaster model* at the hack presenting the record blocks from seating fully. 222 CLINICAL DENTAL PROSTHETICS Fig. 173. - Premature contact of record bfocki at heels support and retain the pins and the upper rim very slightly softened in the area into which the pins will be forced; the blocks are inserted and closed together, and the pins will prevent the sliding movement unless the upper rim has been over-softened. Common Errors in Record Taking Errors in occlusion of the finished dentures frequently arise as a result of errors at the record stage other than an incorrect vertical or antero-posterior dimension. The commonest of these are: (a) Tilting of the blocks off the ridges resulting from uneven contact ( see fig. 172). (£) Premature contact of die heels of the record blocks leading to displacement or tilting of the blocks ( see fig 173). (c) Heavy contact of the heels of the plaster models which prevents them being accurately seated in the blocks (see fig. 174). RECORDING POSITION OF CENTRIC OCCLUSION 223 Fio. 174. - Note contact of the heels of the plaster models at the back preventing the record btocks from seating fully. Chapter VII THE SELECTION OF TEETH At the conclusion of registering the occlusion, the choice of the teeth to be used on the dentures requires to be made. The selection of artificial teeth which are suitable in shape, size and colour is by no means an easy task for the tyro, and presents many difficulties even to the experienced operator if he lacks artistic appreciation. This is an art, not a science, and, whilst the principles which follow will enable any operator of average artistic ability to select teeth which are suitable for the average case, the most pleasing results will always be obtained by the artist. Classification of Patients There are three classes of patients who present themselves for full dentures: (1) Those who still retain most of their upper anterior teeth and whom the prosthetist is going to render edentulous. This group arc considered under ‘Immediate Dentures’. (2) Those who are already wearing full dentures. If the dentures have been worn for any length of time it is probable that the patient, and his immediate circle of relations and friends, are satisfied with the appearance of the dentures, which should thus be copied. It is rarely advisable to make very marked alterations in an individual’s appearance, and improvements are best restricted to the selection of slightly larger teeth of a slightly darker shade. (3) Those who have been rendered edentulous by another operator and who have not yet been supplied with dentures, or who have lost them. The selection of suitable teeth for this group will be considered under the headings: . Shape. Size. Colour. THE SELECTION OF TEETH 22 ' Shape Soon after the introduction of porcelain teeth, to be used in conjunction with vulcanite for full dentures, it was realized that there was some relationship between the shape of the edentulous upper arch and the upper incisor teeth. For example, a V-shaped arch is associated with incisors which arc much narrower at the neck than at the incisive edge; a squarish arch with almost parallel-sided incisors; and a round arch with o\oid teeth {see fig. 175). Fic. 1 75, - Tooth form in relation to arch form. Leon Williams’ Classification The classification of Leon Williams, though not scientifically correct, is undoubtedly the simplest and most useful guide yet suggested, with the added advantage that most manufacturers of artificial teeth have adopted it for their products. Leon Williams claimed that the shape of the upper central incisors bears a definite relationship to the shape of the face. Thus if one of these teeth is enlarged, and the incisive edge placed above the brows with the neck of the tooth on the chin, then the outline of the tooth will nearly coincide with that of the face {see fig. 176). He classified the form of the human face, for simplicity, into three types: Square, tapering, and ovoid. THE SELECTION OF TEETH S 2 7 ear and through the angle of the jaw. If these lines are almost parallel the type is square, if they converge towards the chin the type is tapering, and if they diserge at the chin, ovoid (see fig. 177). Having determined the general type to which the patient belongs it only remains to select teeth which are suitable in length, width and colour, for that individual. SrzE Length and width are the only two dimensions which need to be considered at this stage, the thickness within leason being a variable of no aesthetic importance. This statement must not be taken to mean that the thickness of the anterior teeth is unimportant - it has a considerable bearing on phonetics - but it can be easily varied by the technician without alteration to the form, length or width. Length The length of the upper six anterior teeth is normally such that the necks of the teeth will overlap the anterior ridge by 2-3 mm. cervically, and the incisive edges of the centrals will show below the relaxed lip. The amount of the central incisors visible below the lip is about 3 mm. in a young person and less than half that amount in an elderly patient (see fig. 178). This is not a hard and fast rule, however, and wide variations will frequently be found necessary because the amount of tooth which an individual shows depends on the following factors : Fig. 178. - Amount of tooih * oibJe brJoiv ihc upper lip in. (a) a young patient (6) an elderly patient. 228 CLINICAL DENTAL PROSTHETICS Length, of the Upper Up Some people have long lips which almost completely cover their natural teeth whilst others have short, curved lips which, even in the relaxed position, expose sometimes more than half the length of the teeth. Mobility of the Upper Lip This also is a variable factor. Some individuals expose all the upper anterior teeth and a considerable amount of gum when the^’ smile, others show very little tooth and merely stretch the lips laterally. Vertical Height of Occlusion Reduction in the vertical height will cause the lips to bunch up and cover the teeth, whilst an increase will cause an excessive amount of the teeth to show. Ocerbite A deep overbite results in the exposure of a much greater length of tooth than an edge-to-edge bite. Width Probably the most satisfactory way of selecting teeth of a suitable width for a given case is to choose a set which are wide enough to allow the canines to be mounted on the canine eminence when set up. When using this method, it must be remembered that in very narrow V-shaped mouths, the natural teeth were, in all probability, crowded, and wider teeth should be selected than will reach evenly from one canine eminence to the other: overlapping of the centrals and laterals will enable the canines of the wider set to be placed in their correct positions {see fig. 179). Similarly, to satisfy the above method, excessively broad teeth would be required in very broad mouths, but narrower teeth can be used if they are slightly spaced or if a diastema is placed between the central incisors {see fig. 180). Natural anterior teeth vary greatly in size, but as a rule the)' arc much larger than is generally realized and one of the commonest prosthetic errors is to use teeth which are too small, thus making them appear obviously false. THE SELECTION OF TEETH 220 Fio. 179 Fio. 180 Harmony Having considered the length and breadth as individual factors, the final selection with regard to size should be made according to the general characteristics of the individual’s features, bearing in mind that nature nearly always produces harmony in its work. The relationship between the length and breadth of the face and that of the selected teeth should be studied, and for this purpose the face-length is taken from the supra-orbital ridge line to the inferior border of the chin, and the breadth as the distance between the zygomatic processes. If the length and breadth of the face appear about equal, then the dimensions of the teeth should follow a similar pattern; the face which appears long in relation to its breadth would indicate teeth of those proportions, irrespective of their shape. Colour The natural teeth vary as much in colour as they do in size and shape, and the selection of a suitable shade for any edentulous person is a matter of individual judgment. There are, however, a few generalizations which help the novice whilst he is gaining 230 CLINICAL DENTAL PROSTHETICS experience. Fortunately colour is not critical for the edentulous patient provided that it is not inharmonious with the general colouring of the shin, hair and eyes, and harmony can be obtained over quite a wide range of colour. This statement will be obvious if it is remembered that the natural teeth remain almost constant in colour, merely darkening very slightly with age, but remain in harmony with hair which may first be black, then grey, then white. The colour of the skin may change from a ruddy complexion in health to a greenish- grey pallor in sickness, the same teeth remaining in harmony with both conditions. The following facts are true of nearly all natural teeth, exceptions being very rare: (a) The neck of the tooth has a more pronounced colour than the incisive edge. (b) The incisive edge, if unworn, is more translucent than the body of the tooth and is usually of a bluish shade: this is due to the fact that it is composed entirely of enamel. (r) i| 1 are the lightest teeth in the mouth. are slightly darker. ^ are darker still. 3l3 Posterior teeth are usually uniform in colour and very slightly lighter than the canines. This variation in shade is appreciated by the manufacturers of artificial teeth, most of whom make the desired grading in each set of six anteriors, and the prosthetist selects only the shade of the centrals. More natural and pleasing efiects can often be obtained by using canine teeth of an even darker shade than is supplied in a set of six anteriors. (d) Teeth darken slightly with age. This change has never been satisfactorily explained. There are three dominant tooth colours - yellow, grey, and opal -and each is found in a wide variety of shades and intensity. Many classifications have been made in attempts to THE SELECTION OF TEETH 231 correlate tooth colour with that of the skin, hair and eyes, but only vagu e generalities have remained, for example: (a) Yellow is dominant with fair hair, blue eyes and a fresh complexion. (b) Grey sometimes tinged with blue is dominant with dark hair, brown eyes and dark complexion. (c) Opal is dominant with a clear, pale complexion, irrespec- tive of the colour of the hair and eyes. (lar path parallel to the occlusal plane - contact maintained. (e) Protrusion vwlllt a condytar path sloped at an angle to the occlusal plane - contact lost posteriorly. SETTING-UP THE TEETH 25 1 (d) Centric occlusion with an occlusal surface \%hieh is an arc of the circle of which the condylar path is also an arc, (*) Protrusion of (tic posterior teeth: note how occlusion has been deranged and is now heavy on the lower natural anterior teeth. Waxi,vg-itp * teeth have been mounted in their correct positions a- ■ occlusion, more wax is added to the base and ■ made to conform to certain definite requirements, 'tory of the upper denture must be thick and rounded, > of the posterior palatal border which must J down almost to a knife edge. The buccal and labial ■ be concave to allow for comfortable and free ,, of the buccinator and orbicularis oris muscles. v »*r denture must be similarly finished on the buccal surfaces and periphery, but the lingual surface lined inwards, from above downwards, affording ‘Teas in which the tongue might lodge and unseat Further, the posterior lingual border must be hin edge so that the tongue can move over the and up over the denture without encountering Section (see Chapter II). 256 CLINICAL DENTAL PROSTHETICS Acrylic teeth can be stained and have fillings inserted with ease in the laboratory. The bonding of this material to the denture base is by a chemical union and no stresses occur in the regions of the teeth. So far as anterior teeth are concerned, cither material may be used with safety and satisfaction. The choice between acrylic and porcelain for posterior teeth, however, is not so simple. Porcelain teeth being hard tend to jar on occlusion and transmit the full masticatory load to the ridge. They do not wear into a smooth even articulation easily to accommodate a slightly uneven occlusion when the dentures are fitted, or changes of articulation, due to bone resorption, throughout the life of the dentures, although polished facets do develop on them slowly. Porcelain teeth do, however, maintain the vertical occlusal dimension and arc hard and sharp enough to produce efficient mastication. Acrylic teeth produce a cushioning effect when chewing somewhat akin to that provided by the periodontal membrane in natural teeth. They wear to accommodate changes in occlusion, but unfortunately they usually wear so rapidly that they allow the vertical dimension to close {see fig. 199(a)), and they do not produce efiicicnt mastication. In the opinion of the authors the rapid wear of acrylic posterior teeth resulting in loss of vertical dimension and eventually uneven occlusion is a serious fault, and for this reason alone such teeth should not as a general rule be used. In cases presenting narrow painful ridges or in the aged, when the biting power is small, or where the ridge needs cushioning, a case may be made for them. The claim that the wear of acrylic teeth is supposed to allow the occlusion to adjust itself to the gradual closure of the vertical dimension which occurs slowly throughout the life of the denture, due to the ridge absorption, is not in practice usually substantiated. Anyway dentures should never be worn for so long that gross closure of the vertical dimension due to ridge absorption is allowed to occur, for in these cases the denture bases will be so poor a fit on the ridges that they will cause damage. As a general rule most dentures require replacing within three to five years. SETTING-UP THE TEETH 25 / Fic. 199(a). - The wear of acr>bc posterior teeth: note how the occlusion has been deranged and is now heavy on the lower natural anterior teeth. Waxing-up When the teeth have been mounted in their correct positions and in proper occlusion, more wax is added to the base and the whole made to conform to certain definite requirements. The periphery of the upper denture must be thick and rounded, with the exception of the posterior palatal border which must be thinned down almost to a knife edge. The buccal and labial surfaces must be concave to allow for comfortable and free movement of the buccinator and orbicularis oris muscles. The lower denture must be similarly finished on the buccal and labial surfaces and periphery', but the lingual surface must be inclined inwards, from above downwards, affording no undercut areas in which the tongue might lodge and unseat the denture. Further, the posterior lingual border must be finished to a thin edge so that the tongue can move over the mylohyoid ridge and up over the denture without encountering any distinct projection (see Chapter II). 258 CLINICAL DENTAL PROSTHETICS Gum-fitted Anterior Teeth In some patients the maxilla is overdeveloped in the incisor region, and if a wax flange is placed over this region it pushes the upper lip out, making the patient appear to have a swollen lip. In these cases the six upper front teeth are fitted directly on to the alveolar ridge without any labial flange {see fig. 199(6)). Retention of this type of denture is usually impaired owing to the peripheral seal being more readily broken, and the loss of the stabilizing effect of the labial flange. Sometimes two extensions, known as ‘wings’, are added in an attempt to overcome these deficiencies 199M). Setting up the Teeth for Abnormal Jaw Relationships When the models have been articulated, after taking the records it will be found in a considerable number of cases that they present deviations from the normal relationship and thus present problems in setting up and articulating the teeth. Superior Protrusion The lower ridge is narrower than the upper and associated with a receding chin. SETTING-UP THE TEETH ? 5 ? Selling the Posterior Teeth The upper posterior teeth will need to be set inside the ridge, in order that they may occlude with the lower teeth. The lower teeth should never be set outside the ridge (see fig. 200). Setting the upper teeth inside the ridge does not produce F«j. son. - Upper poitenor teeth tel slightly lnIar and incisive guidance botli of 30 6 . The paths represent in ascending order those of the lit premolar, and premolar, 1st molar, and and molar teeth. The left side in the dtaeram is the balancing side and the right the working side, because on the articulator it is the upper frame which motes Fig. 233 shows how they maintain balance when in balancing occlusion, and fig. 234 when in working occlusion. The palatal inclines of the maxillary teeth, and the buccal inclines of the mandibular teeth, must be parallel to the path AB, and the buccal inclines of the maxillary teeth, and the lingual inclines of the mandibular teeth, must be parallel to the line CB. Fig. 235 shows how cuspal interference will occur if teeth arc set to a horizontal occlusal plane, and how the introduction of the lateral compensating curve corrects this. Fig. 236 shows how' cusp locking can also occur in a pro- trusive movement if the anteroposterior cuspal angles arc not in harmony with the protrusive path of the mandible. The Setting of the Indsal Guide Table From the foregoing it will be realized that the angle of the incisal guide table will markedly affect the cusp angles. 294 CLINICAL DENTAL PROSTHETICS Fig. 331. - Diagrammatic representation of the paths of the posterior teeth during a lateral mandibular movement with a condylar guidance or 30® and an incisive guidance of 3®. AB represents the path followed by the and pretnolar tooth when the left side, in the diagram, is acting as the balancing side, and CB represents the path followed by this tooth when the left side b acting as the working side. cusp heights, the overbite and the oveijet. The question, therefore, is how it is set for any given case. The way to do this is as follows: Set up the upper and lower six front teeth to the required overbite and overjet, and then alter the incisal guidance tabic so that in protrusion, and right and left lateral movements, the incisive edges of the upper and lower teeth just slide upon one another. Remember, however, that the steeper the slope of the guidance table, the higher and steeper will need to be the cusps of the molar teeth, and even with balanced articulation high steep cusps are habfe to cause instability. Therefore, when setting the teeth, make the overbite as small as possible. This is particularly true when the mandible is fiat and almost entirely ridgeless, where in extreme cases the posterior teeth must be virtually cuspless if functional stability is to be attained. 2g6 CLINICAL DENTAL PROSTHETICS Fig. 235 (a) Teeth set with long axes vertical. Cuspal inclines not parallel to planes of movement. (b) Long axes of teeth inclined to lateral compensating curve. Cuspal inclines are now parallel to planes of movement. Fig. 236. — Diagrammatic representation of cusp locking and loss of cuspal contact. MP = mandibular path. (a) The cuspal inclines arc parallel to the mandibular path and therefore tooth contact can be maintained during mandibular movement. (t) The cuspal inclines are of a lesser angle to the horizontal than the mandibular path, thus tooth contact will be lost dunng mandibular movement. (e) The cuspal inclines are of a greater angle to the horizontal than the mandibular path; thus cusp locking occurs if mandibular movement is attempted. ANATOMICAL ARTICULATION 297 4. Teeth for Anatomical Articulation Several varieties of teeth have been manufactured especially for use with anatomical articulators, and their cuspal angles are arranged to facilitate occlusal balance; in a few instances the angle which the cuspal plane makes with the horizontal plane is stated. Cusped Teeth A cusped posterior tooth should generally be used in preference to a cuspless one for two reasons: (a) Greater efficiency. ( b ) Balance is more easily obtained. (a) Greater Efficiency. - A convex surface makes point contact with a flat or convex surface, and this point contact, moving under pressure, results in a cutting action. The cusps also produce a grinding action when moving through the intcr- cuspal spaces which help to hold the food in position whilst it is being ground. Provided that the cusps and sulci are correctly shaped, there is ample clearance space for the ground and cut particles to escape from the occlusal surfaces. Flat, cuspless teeth, whilst able to crush and grind food, cannot possibly cut vegetable or animal fibres, which must therefore be reduced to a length suitable for swallowing before being placed in the mouth. ( b ) Balance. - With cusped teeth it is a simple matter to obtain a balanced articulation and to perfect it by grinding any points of contact where pressure may be slightly excessive. With cuspless teeth it is very difficult to obtain a balance and the most satisfactory way of doing so is to use a technique employing plaster of Paris and pumice record blocks which will shortly be described. Final adjustment of these cuspless surfaces is difficult, as the surface contacts arc so broad. Inicrted Cusped Teeth There are several makes of teeth, which are described as having ‘inverted cusps’ which are in eflect flat-surfaced teeth with hollows ground into the occlusal surface. The claim is made for these teeth that food fibres are cut between the edges of the hollows, whilst the flat surfaces allow lateral movements 2 9^ CLINICAL DENTAL PROSTHETICS without cuspal interference. With most teeth of this type the first claim is quite inaccurate as the hollows arc not provided with escape grooves for the food, and consequently immediately become filled up and clogged. The second claim is correct in that they Avail avoid cuspal interference, but on the other hand it is difficult to grind these flat surfaces to give balanced articulation. Plaster Record Rim Technique The techniques which have been described so far have all left the degree of curvature of the compensating curves to the discretion of the technician, whilst the object of this technique is to obtain the individual curs es of a given patient. Briefly, this is attained by inserting record blocks with friable rims and allowing the patient to grind them together until they arc in balanced articulation. 1. Bases Stability of the record blocks is essential for accuracy since there will be a considerable lateral and protrusive drag, owing to friction, during the process of grinding and, therefore, the bases should be made of acrylic resin. 2. Rims These are made of a mixture of plaster of Paris and an abrasive, the latter being coarse carborundum, pumice or sand and a suitable mixture which is fairly strong, and quick cutting, is Go per cent artificial stone with 40 per cent carborundum. The width should be approximately 1 cm. which is necessary to define the lateral curves and is also required for strength. It is essential when employing this technique that the jaw relationship is first recorded using wax blocks and the blocks with abrasive rims arc constructed to models mounted to the correct jaw relationship hot with the vertical height opened by about 5 mm. to allow for the closure which will result from the grinding. The plaster rims should be allowed to set for at least twenty- four hours before being used and should then he painted, except on the occlusal surfaces, with three coats of sandarac ANATOMICAL ARTICULATION 2C$ varnish. This varnishing helps to prevent crumbling of the rims during grinding, particularly on the edges of the occlusal surfaces. Another method of constructing the rims is to make them of composition to within 6 mm. of the estimated correct height, to groove the composition for retention and then build up"the plaster-pumice for a further i cm. (see fig. 237). PLASTER & ABRASIVE COMPOSITION Tic. 237. — Details of the construction of a plaster bite rim. 3. Grinding The patient is instructed to grind the blocks together with both lateral and protrusive movements but only to use the minimum pressure necessary to keep the blocks in contact. The necessity for using very light pressure must be emphasized since the high proportion of abrasive which is needed for rapid cutting very materially weakens the plaster which will crack or crumble if anything approaching full masticatory pressure is used. Denture adhesive is useful to assist stability of the blocks, or the operator may support the blocks with his fingers to prevent any movements in the preliminary stages of grinding. The patient should be instructed not to swallow the debris, and the record blocks must be removed from time to time for cleaning and inspection and to allow the patient to rinse his mouth and also to rest. The grinding should be continued until the correct vertical height is obtained which will usually be accomplished within ten minutes. The occlusal surfaces of the rims now show correct balancing curves for that individual ( see fig. 238) which arc reproduced in the denture by mounting the lower teeth to occlude with the upper block and then the upper teeth to occlude with the lower ones (see fig. 239). 300 CLINICAL DENTAL PROSTHETICS 1 1C. 239- - Lo"cr teeth set to upper ground in block. It should be appreciated that there are numerous balancing curves suitable for every individual and that curves obtained by this grinding technique under different conditions arc not interchangeable. The form of curve will vary with the height of the occlusal surfaces and also with the original shape of the plaster-pumice blocks, whether flat or curv ed. Chapter X PHONETICS Mechanism or Speech The voice is principally produced in the larynx, whilst the tongue by constantly changing its shape and position of contact with the lips, teeth, alveoli and hard and soft palates, gives the sound form and influences its qualities. The oral cavity and the sinuses act as resonant chambers, and the muscles of the abdomen and thorax control the volume, and rate of flow, of the air stream passing into the speech mechanism. The soft palate in conjunction with the pharynx controls the direction of the air stream after it passes from the larynx. In all the vowel, and most consonant sounds, the air stream is confined entirely to the oral cavity, but a few nasal sounds do occur, c.g. M, N, and NG, in which the air is expelled mainly through the nose. The former arc produced by raising the soft palate into close contact with the pharynx, thus scaling off the nose and forcing the air to proceed through the mouth. With the nasal sounds the soft palate is pressed downwards and forwards and the dorsum of the tongue humped up to meet it, thus scaling ofT the oral cavity and forcing the air stream to proceed through the nose. The vowel sounds A, E, I, O, U are formed by a continuous air flaw, the alteration in size of the mouth and the change in shape and size of the lip opening giving the various sounds their characteristic form. The consonant sounds are produced by the air stream being stopped in its passage through the mouth by the formation of complete or partial seals or stops. These are produced by the tongue pressing against the teeth or palate, or by the closing of the lips. The sudden breaking of the seal brought about by the withdrawal of the tongue, or the opening of the lips, produces the sound. In many sounds there is a build up of air PHONETICS 303 pressure behind the stop which when the seal is released produces an explosive effect. Examples of these are: the lip closure of the P and B sounds; the tongue and anterior hard palate contact in T and D sounds. In some cases the seal or stop is not complete, but the channel through which the air stream must pass is made extremely narrow: an example of this is the production of an S, Z, or C soft sound, in which the tongue separates itself from the anterior aspect of the hard palate by about 1 mm., forming a thin slit-like channel through which the air stream hisses. Speech, therefore, is largely a matter of the control of the size and shape of the mouth, which is chiefly governed by the position of the tongue and its contact with the teeth, alveoli and palate. Fortunately for the prosthetist, the tongue possesses remark- able qualities of adaptability, and rapidly becomes accustomed to changes occurring in the mouth. After the extraction of teeth, or the insertion of a denture, some difference may be noticed in the quality of the speech, but improvement quickly follows as the tongue adjusts itself to the new conditions. In extreme cases, such as the edentulous state or when poorly designed complete dentures are worn, the previous tone and quality are not always re-established. The tongue’s adapta- bility is illustrated by the number of individuals wearing dentures, designed with little regard to their effect on phona- tion, who exhibit no obviously apparent speech defects; the reason being that in the construction of those dentures the general principles of setting up were followed, coupled with due regard to the aesthetic requirements and the attainment of the correct vertical dimension. This has produced the occlusal plane at a level corresponding to that of the natural dentition, the anterior teeth in approximately the same position a n tcropostcriorl y as the natural teeth, and the new dental arch conforming to that of the previous arch, thereby allowing the correct tongue space. Thus the artificial dentures replacing the lost tissues have conformed closely to the state which existed naturally, the main difference being the increase in bulk — a factor for which the tongue must compensate. 3°4 CLINICAL DENTAL PROSTHETICS However, some knowledge of phonetics in relation to dentures is necessary, in order to correct the speech defects that mav occur in denture wearers, and also to act as a guide for the more accurate construction of complete dentures. The Factors in Denture Construction Affecting P/fO.VATTON The Voxel Sounds These sounds are produced by a continuous air stream passing through the oral cavity which is in the form of a single chamber for the A, O, U sounds and a double chamber for the I and E sounds, the division occurring through the dorsum of the tongue touching the soft palate in the post-dam region. The lip of the tongue, in all the vowel sounds, lies on the floor of the mouth cither in contact with or close to the lingual surfaces of the lower anterior teeth and gums. The application of this in denture construction is that the lower anterior teeth should be set so that they do not impede the tongue positioning for these sounds; that is, they should not be set lingual to the alveolar ridge. Since the vowels E and I necessitate contact between the tongue and soft palate, the upper denture base must be kept thin, and the posterior border should merge into the soft tissue in order to avoid irritating the dorsum of the tongue, which might occur if this surface of the denture was allowed to remain thick and square-ended. The Consonant Sounds For convenience, these sounds may be classified thus: (a) Labials Formed mainly by the lips (c.g. B, P, M). lb) Labiodentals Formed by the lips and teeth (e.g. F, V, Ph). (r) Linguodentah Formed by the tongue and teeth (e.g. Th). (d) Linguopalalals Formed by the tongue and palate. (i) Tongue and anterior portion of the hard palate (c.g. D, T, C (soft), S, Z, R). PHONETICS 305 (fi) Tongue and portion of the hard palate posterior to that of (i) (e.g. J, CH, SH, L, R). (iii) Tongue and soft palate (e.g. C (hard), K, G, NG). (e) Nasal (e.g. M, N, NG — also belonging to the other groups). Unless careful consideration is given to the following aspects of denture construction, speech defects will occur varying from the almost indiscernible to the unpleasantly obvious. I. Denture Thickness and Peripheral Outline The prosthetist’s aim is to produce dentures which are mechanically functional, aesthetically pleasing and permit normal speech. The most satisfactory attainment of the first two requirements may cause slight defects in the patient’s speech but this should not be allowed to happen and some com- promise will often be required satisfactorily to balance these three aims. One of the reasons for loss of tone and incorrect phonation is the decrease of air volume and loss of tongue room in the oral cavity resulting from unduly thick denture bases. The periphery of the denture must not be overextended so as to encroach upon the movable tissues, since the depth of the sulci will vary with the movements of the tongue, lips and cheeks during the production of speech sounds. Any interference with the freedom of these movements may result in indistinct phona- tion, especially if the function of the lips is in any way hin- dered. Most important is the thickness of the denture base covering the palate, for here no loss of natural tissue has occurred, and the base reduces the amount of tongue space and the oral air volume. The palate in this instance does not include that part Forming the tooth-bearing area - artificial alveolus. The production of the palatolingual group of sounds involves contact between the tongue, and either the palate, the alveolar process, or the teeth. With the consonants T and D, the tongue makes firm contact with the anterior part of the hard palate, and is suddenly drawn downwards, producing an explosive sound; any thickening of the denture base in this region may cause incorrect formation of these sounds. When producing the S, G (soft), Z, R and L consonant sounds, contact occurs between the tongue and the most anterior part of the hard 3° 6 clinical dental prosthetics palate,' including the lingua! surfaces of the upper and lower incisors to a slight degree. In the case of the S, C (soft), and 7. sounds, a slit-like channel is formed between the tongue and palate through which the air hisses. If the artificial rugae arc over-pronounced, or the denture base too thick in this area, the air channel will be obstructed and a noticeable lisp may occur as a result. To produce the Ch and J sounds the tongue is pressed against a larger area of the hard palate, and in addition makes contact with the upper alveolar process, bringing about the explosive effect by rapidly breaking the seal thus formed. The Sh sound is similar in formation, but the air is allowed to escape between the tongue and palate without any cxplosi\c effect, and if the palate is too thick in the region of the rugae, it may impair the production of these consonants. 2. Vertical Dimension The formation of the labials P, B and M require that the lips make contact to check the air stream. With P and B, the lips part quite forcibly so that the resultant sound is produced with an explosive effect, whereas in the M sound lip contact is passive. For this reason M can be used as an aid in obtaining the correct vertical height since a strained appearance during lip contact, or the inability to make contact, indicates that the bite blocks are occluding prematurely. With the C (soft), S and Z sounds the teeth come very close together, and more especially so in the case of Ch and J; if the vertical dimension is excessive, the dentures will actually make contact as these consonants are formed, and the patient will most likely com- plain of ‘clicking teeth’. 3. The Occlusal Plane The labiodentals, F, V and Ph, arc produced by the air stream being stopped and explosively released when the lower lip breaks contact with the incisal edges of the upper anterior teeth. If the occlusal plane is set too high the correct positioning or the lower lip may be difficult, iron the other hand the plane is too low, the lip will overlap the labial surfaces of the upper teeth to a greater extent than is required for normal phonation and the sound might be affected. PHONETICS 307 4. The Anteroposterior Position of the Incisors In setting the upper anterior teeth consideration or their labiopalatal position is necessary for the correct formation of the labiodental F, V and Ph. If they are placed too far palatally the contact of the lower lip with the incisal and labial surfaces may be difficult, as the lip will tend to pass outside the teeth: the appearance usually prevents the operator from setting these teeth forward of their natural position. If the anterior teeth are placed too far back some effect may be noticed on the quality of the palatolinguals, S, C (soft), and Z, in which the tip of the tongue makes slight contact with the upper and lower incisors: this will result in a lisp due to the tongue making contact with the teeth prematuiclv. The tongue will more readily accommodate itself to antero- posterior errors in the setting of the teeth than to vertical errors. 5. The Post-dam Area Errors of construction in this region involve the vowels I and E and the palatolingual consonants K, NG, G and C (hard). In the latter group the air blast is checked by the base of the tongue being raised upwards and backwards to make contact with the soft palate. A denture which has a thick base in the post-dam area, or that edge finished square instead of tapering, will probably irritate the dorsum of the tongue, impeding speech and possibly producing a feeling of nausea. Indirectly the post-dam seal influences phonation, for if it is inadequate the denture may become unseated during the formation of those sounds having an explosive effect, requiring the sudden repositioning of the tongue to control and stabilize the denture; this applies particularly to singers. Incidentally, speech is usually of poor quality in those individuals W’hose upper denture has become so loose that it is held in position mainly by means or tongue pressure against the palate. Careful observation will show that the denture, in such cases, rises and falls with tongue movements during speech. Before passing to the next factor it should be mentioned that the consonants M, N, NG also belong to the nasal group in which the air stream is allowed to escape into the nasal cavity 3°8 CLINICAL DENTAL PROSTHETICS through a slight channel formed by the incomplete approxi- mation of the soft palate and pharynx. 6. Width of Dental Arch If the teeth are set to an arch which is too narrow the tongue will be cramped, thus afTecting the size and shape of the air channel; this results in faulty phonation of such consonants as T, D, S, M, N, K, C and H, where the lateral margins of the tongue make contact with the palatal surfaces of the upper posterior teeth. Every endeavour should be made, consistent with the general mechanical principles, to place the lingual and palatal surfaces of the artificial teeth in the position previously occupied by the natural dentition. 7. Relationship of the Upper Anterior to the Lower Anterior Teeth The chief concern is that of the S sound which requires near contact of the upper and lower incisors so that the air stream is allowed to escape through a slight opening between the teeth. In abnormal protrusive and retrusivc jaw relationships, some difficulty may be experienced in the formation of this sound, and it will probably necessitate adjustment of the upper and lower anterior teeth anteroposterior!)', so that approximation can be brought about successfully. The consonants Ch, J and Z require a similar air channel in their formation. Summary To summarize, it will be seen that speech requirements call for dentures having a correct vertical dimension, an accurate periphery and an arch formation permitting natural tongue space, so that adequate freedom for movement is ensured. The position of the anterior teeth should be such that they follow that of the natural teeth, thus fixing the occlusal plane at the correct level and preventing the placing of the artificial teeth inside or outside the natural arch, which would require the tongue to adapt itself to new circumstances. Finally, denture bases should be fashioned suitably thin, but consistent with the other factors of denture construction, so that contact by the tongue takes place in as near a natural and normal manner as is possible. Chapter XI TRYING IN THE DENTURES Having set-up the teeth according to the information secured at the record stage, it is necessary to try the waxed-up dentures in the patient’s mouth before finishing them, so that they may be checked. Once the dentures have been processed it is laborious and difficult to effect any alterations, whereas in the waxed-up stage changes can easily be made. Since so many points require checking, it is sound practice to get into the habit of working to a definite plan, and the following order is suggested: 1. The Lou.tr Denture By Itself. Check - (a) Peripheral outline (i) Buccal and labial. (ii) Lingual. (iii) Posterior extension. {b) Stability to occlusal stresses. (i c ) Tongue space. (d) Height of the occlusal plane. 2. The Upper Denture By Itself. Check - (а) Peripheral outline (i) Buccal and labial. (ii) Posterior border. (б) Stability to occlusal stresses. 3. Both Dentures Together. Check - (a) Position of occlusion (i) Horizontal relationship. (ii) Vertical height. 309 3 10 CLINICAL DENTAL PROSTHETICS (b) Evenness of occlusal pressure. (c) Balanced occlusion (anatomical articulation only). (' d ) Appearance (i) Centre line. w (ii) Anterior plane. (iii) Shape of the teeth. (iv) Size of the teeth. (v) Shade of the teeth. (yi) Profile. , r {vii)_ Amount of tooth visible. ' (viii) Regularity of the teeth. (f) Approval of appearance by the patient. Before carrying out these checks, remove the dentures from the articulator and place them in a bowl of cold water. It is important that ‘waxed-up’ dentures should be frequently placed in cold water as wax softens appreciably at mouth temperature and, if left in the mouth too long, the teeth may be displaced. The method of carrying out these checks is as follows: i. Trying in the Lower Denture By Itself Place the denture in the mouth and seat it on the ridge. (a) Check the Peripheral Outline The entire periphery should be checked to ensure that it is not over, or under, extended. (i) The Buccal and Labial Periphery. - Hold the denture in place with light pressure on the occlusal surfaces of the teeth, and move the cheek on one side gently, but firmly, upwards and inwards, thus simulating the motion it makes when chewing. Now relax the pressure on the teeth and observe if the denture rises from the ridge. If it does, trim the periphery where it is seen to be overextended until little or no movement occurs. Pay particular attention to the buccal fraena and ensure that they have adequate clearance. Repeat for the opposite side and for the lip. Note the bulk and shape of the buccal aspect of the denture. It should take the form of a gentle concavity looking outwards and upwards (see Chapter II). Such a contour will aid the retention of the denture as the cheek will tend to fit into the concavity and hold the , denture down. TRYING IN THE DENTURES 3 1 1 (ii) The Lingual Periphery. - Hold the denture in' place with light pressure and ask the patient to protrude in’s tongue sufficiently to moisten his lips; if the denture lifts at the back, it is overextended in the region of the lingual pouch. Next, ask the patient to put the tip of his tongue as far back on his palate as possible; if the denture lifts in the front, it is over- extended anteriorly, probably in the region of the lingual fraenum. Such overextension must be relieved, but care should be taken to avoid over-trimming, which is scry easily done owing to the difficulty of seeing the functional depth of the lingual sulcus when the denture is in place. Final adjustments arc more easily and more accurately made after the finished denture has been worn for a few days, when areas of slight inflammation will indicate the precise location of overextension. (iii) Posterior Extension. - Ensure that the heels or the lower denture arc extended as high up the ascending ramus of the mandible as is practicable. The purpose of this is to buttress the denture against the backward pressure of the lower lip (see fig. 240). (iv) Under Extension. - Though of less common occurrence than over extension it is equally important that the periphery should not be under extended since dentures must cover the 3*3 TRYING IN TIIE DENTURES The causes of longue cramping: (i) Posterior teeth set inside the ridge. (ii) Molar teeth which are too broad buccolingually. Such teeth should be replaced by smaller ones or their width reduced by grinding. (hi) Molar teeth leaning inwards. This will not always cause cramping of the tongue but should never be allowed to occur as it interferes with the free vertical movements of the tongue. If this inw ard inclination is necessary to obtain occlusion, it is best to finish the denture and then grind away the lingual cusps (see % 241). Fjg. 34 1 (0) An o\ changing lingual cusp allowing the tongue to get underneath and lift the denture. (1) The cusp has been ground away. (d) Height of the Occlusal riane To obtain maximum stability of a lower denture, the occlusal plane of the lower teeth should be very slightly below the bulk of the tongue, so that the tongue performs the majority of its movements above the denture and thus tends to keep the denture down ( see fig. 242). The denture must therefore be examined to sec if the tongue, when relaxed, lies above or below the occlusal plane. Ask the patient to relax and place the tip of the tongue comfortably and without strain behind the lower front teeth, which is the normal relaxed position of the tongue, and then open his month without moving his tongue. If the height of the occlusal plane is correct, the tongue will be seen to lie on top of the lingual cusps. If the lower denture still tends to rise unduly after the lingual periphery has been trimmed, and as much lateral 3 f 4 CLINICAL DENTAL PROSTHETICS Flo. 242. - Low occlusal plane allows tongue to rest on occlusal surface. space as possible for the tongue has been allowed, it may be necessary to rc-set the case completely, lowering the occlusal plane. The height of the occlusal plane is also of importance for the following reason : the greater the height of the lower denture, the longer will be the lower front teeth and the greater therefore the surface exposed to the pressure of the lower lip. This concludes the examination of the lower denture alone, and it should be removed from the mouth and placed in a basin of cold water. 2. Trying in the Upper Denture by Itself Place the upper denture in the mouth and examine as follows: (a) Check the Peripheral Outline (i) The buccal and labial periphery is checked as for the lower denture. (ii) Position of Posterior Border. - Verify carefully that the posterior edge is correctly situated on the soft palate and that the post-dam area on the model has been placed correctly ( see fig. 243). (b) Check the stability to occlusal stresses, as for the lower denture, but if the teeth have been set outside the ridge for reasons dic- tated by the occlusion or to enhance the appearance then this test will obviously be omitted and reliance will be placed on the positive retention of the finished denture to produce stability. TRYING IN THE DENTURES 3*5 Fig. 243. - Showing posterior edge of upper denture correclls post-dajTiincd. 3. Both Dentures Together Remove the upper denture from the mouth and chill in cold water for a few seconds, and then place both dentures in the mouth. If it is found necessary to improve the retention of the dentures when using a shellac type of base-plate, some adhesne powder may be sprinkled on their fitting surfaces. (a) Position of Occlusion (i) Check the Anteroposterior Relation. - Hold the lower denture in position on the ridge and ask the patient to relax, then to close the teeth together gently and maintain them in occlusion whilst the examination is carried out. If the bite registration w'as accurate, the teeth should interdigitate in the mouth in exactly the same manner as they do on the articulator, but if the registration was wrong, the teeth will not interdigitate correctly and may even occlude cusp to cusp on one or both sides. The operator must make quite certain that the occlusion he sees in the mouth is not due to movement of the dentures on the ridges, tilting of either denture or dropping of the upper demure. This is best tested by asking the patient to keep the teeth together and then trying to separate the posterior teeth by means of a thin spatula or knife; this test should be carried out on each side of the mouth alternately. The teeth should be brought into occlusion several times, using any of the registration aids which can be adopted at this stage, in order to make certain that the position of occlusion is correct or, if it is incorrect, to ascertain the type of error, i.e. whether the mandible can be rctruded from the previously recorded jaw relationship or whether a lateral swing has occurred. Observation of the upper and lower centre lines in relation 3*6 CLINICAL DENTAL PROSTHETICS to each other, with the dentures on the articulator and then in the mouth, will indicate a lateral swing, if present. When the lower centre line is seen to be to one side of the upper centre line, with the dentures in the mouth, in contrast to the coincidence of these lines when viewed on the articulator, it is possible that the original registration was incorrect and that of a lateral position was recorded; this may be checked by the occlusion of the posterior teeth. If the original posi- tion was incorrect, the lower cusps will be slightly farther back on one side indicating a fuller retrusion of the condyle on that side. Should the lower cusps be slightly forward on one side, it indicates that the original recording of the occlusion was correct and the patient is now giving a lateral position (see fig. 244). Major errors in the position of occlusion are easily detected, but minor errors may pass unnoticed; therefore it is extremely important to watch for any slight movement of the dentures on their respective ridges from the time the teeth first make contact until they reach the position of complete inter- digitation, the reason being that the cusp inclines of the teeth guide the dentures into occlusion and will move the dentures (a) RIGHT SIDE LEFT SIDE (f>> AW Fig. 244. - Incorrect recording or the occlusion (lateral mandibular swing) as it appears at the try-m stage - (a) A right swing seen from the front -note lack of con- tinuity upper and lower centre lines. (fe) A right swing seen from the side. Posterior teeth on left side still interdigitate but hate shifted laterally. Those on right do not mterdigitate. TRYING IN THE DENTURES 317 in relation to the ridges when only a slight error of jaw relation- ship exists from that which was obtained when taking the records. Care is needed when holding the lower denture in place on the ridge to avoid pushing it backwards. When errors of occlusion are noted at the try-in stage they must be corrected by re-taking the position of occlusion. Re-taking the anteroposterior position: The dentures arc seated on the models on the articulator and the posterior teeth removed from one of the dentures and replaced by wax blocks, which should be trimmed to occlude with the posterior teeth of the other denture without altering the \crtical dimen- sion as set on the articulator (see fig. 24.5). In this wa> con- Ftc 245 sidcrablc time may be saved in trimming the blocks in the mouth, as then only minor adjustments arc necessary to produce evenness of occlusal pressure. The position of occlusion is recorded by adding a little softened carding, or base-plate w'ax to the chilled blocks, placing the dentures in the mouth and asking the patient to close together, thus impressing the cusps of the opposing teeth into the soft wav (see fig. 2 }6). Tic. 24G 3*^ CLINICAL DENTAL PROSTHETICS The chilled wax blocks in occlusion with the opposing teeth will prevent any alteration in the vertical height. Care must be taken to see that the new- position of occlusion gives the necessary correction. Points which may aid in this are -obser- vations of overbite, overjet, and the relation of the centre lines. When correcting a lateral swing care must be taken to see that the lower anterior teeth do not impinge on the upper teeth, as this may cause the mandible to be guided into an incorrect position, or the dentures to tilt. If any contact of the anterior teeth occurs the offending lower teeth should be removed and the position re-taken. (ii) Check the Vertical Height. - Ask the patient to relax with the lips closed. Watch the point of the chin and then ask the patient to close the teeth together; the chin should move upwards a small but definite amount [see Chapter VI). If it is impossible to obtain this movement in spite of repeated attempts, it can be assumed that the vertical height is too great, and, if this is gross, there will also be a strained appear- ance when the lips arc brought into contact with each other. It should be remembered that patients who are mouth breathers relax with their lips parted, and frequently have a large free-way space. An overdosed vertical height will be associated with an excessive free-way space, and when the teeth are in occlusion the lips will be seen to be pressed too firmly together with some loss of the vermilion border. Correcting the vertical height: The posterior teeth are removed from one of the dentures and replaced by wax blocks. The articulator should be closed or opened approximately the amount required to establish a suitable free-way space, and the blocks then trimmed to occlude with the opposing teeth at the new vertical height. Final adjustments for evenness of occlusal pressure, and for the production of the correct free- way space, are carried out in the mouth. Once these are satisfactory', the record blocks should be chilled in cold water, and a little soft wax added to their occlusal surfaces to register the impressions of the opposing teeth when registering the position of centric occlusion. The chilled blocks resist the pressure of occlusion during this stage and prevent over-closure. TRYING IN THE DENTURES 319 With cases set on an anatomical articulator the articulator may be closed or opened 2-3 mm. without taking a further occlusal registration, provided the face-bow and condylar records are correct: the reason being that the articulator reproduces the patient’s individual jaw and temporo-mandibu- lar joint relationships, and that a closure or opening of 2-3 mm., on the articulator, will produce no appreciable difference in the balance of the finished dentures, since such changes of vertical dimension occurring in the patient may be con- sidered as a simple hinge-type movement. (£} Evenness of Occlusal Pressure Provided centric occlusion is correct, the evenness of the occlusion is next checked. As the teeth close, they should occlude evenly and with equally distributed pressure all round. It frequently occurs that the teeth on one side of the mouth occlude slightly before those on the other, or the molars before the prcmolars. This may be due to: (i) Pressure on the blocks being heavier on one side than the other when the records were taken. (ii) A slight error in sealing the models in the blocks when articulating them. (iii) Warpage of the base-plates. Such errors may escape notice at the try-in stage because the waxed-up dentures will readily tilt because the retention of the base-plates is less than that of finished dentures, thus allowing the waxed-up teeth to be in occlusion when in fact they should not be in contact on the side on which the dentures have tilted ( see fig. 247). Such irregularity of pressure may be slight or very considerable, but if it escapes notice at the try-in stage, when the dentures are finished the teeth will be held apart in the area of heavy' pressure and may require excessive grinding to correct this: it may be so gross as to necessitate completely' re-making one of the dentures. Teeth out of contact in the incisor and premolar region, due to the molars occluding too early, is frequently due to this cause {see fig. 248). To test for evenness of occlusal pressure, proceed as follows: Place two pieces of thin celluloid strip between the teeth in 3=0 CLINICAL DENTAL PROSTHETICS Fig. 347. ~ Section through a full upper and lower demure at the fr> -in *tage. Inspection in the mouth would reveal apparent!) eten eonixet between the molar teeth on both sides. What hat anuallv occurred, however, it that I .raw pressure on the right side hat rauvd the lower denture to lift from the ridge on the left tide until the teeth male contact The ute of celluloid atrip* to rhrrJk terJuuJ prewtrr* »• all reveal tuch an error. Fig sa8 - An anterior open 'bite* due to tl e molar* occluding the molar region, one on each side. Request the patient to dose and then endeavour to remove the celluloid strips simul- taneously, holding one with each hand, by pulling them out between the closed teeth. Any diflerrncc in the force required to remove the strips will be readily appreciated, and if this force is interpreted in terms of occlusal pressure, an assessment may be made of whether or not it is even. Repeat the test in the prcmolar regions. TRYING IN THE DENTURES 321 To test whether the front of the denture is rising slightly from the ridges when the back teeth are occluding, insert the point of a wax knife between the upper and lower incisor teeth and attempt to push the upper denture upwards and the lower denture downwards. Any appreciable movement may be interpreted as excessive pressure in the molar region. Correcting unevenness of pressure; If it is slight, gently soften, with a pin-point flame, the wax supporting the teeth of one of the dentures on the offending side. Replace the dentures in the mouth and, holding the lower firmly in place, request the patient to close. The teeth on the side of heavy pressure will sink slightly into the softened wax until the occlusion of the teeth on the opposite side arrests them, thus evening the occlusal pressure. If the unevenness is more than slight, this technique will not serve, as the teeth will be forced out of place. Complete re-taking of the record of centric occlusion with built-up wax blocks is the only solution. In cases in which difficulty is experienced with the position and evenness of occlusion it frequently simplifies the problem if the upper denture is finished first and then the waxed up lower denture is re-tryed against this demure. Small altera- tions in the occlusion can easily be made to the waxed up lower denture before it is finished, and with the closely fitting, well retained upper denture in place patients seem to find it simpler to produce a correct position of occlusion. (c) Balanced Occlusion and Articulation (anatomical articulation only) The first check is for centric occlusion, which, if found to be incorrect, necessitates the removal of the lower posterior teeth and the recording of the correct position on the wax blocks replacing them. The lower model is then removed from the articulator and re-set according to the new’ position, thus keeping the upper model in the same position as it was set by means of the face-bow. When the centric position is found to be correct, the testing of the waxed-up denture continues in the following manner: Check for evenness of occlusal pressure in the centric position with celluloid strips and then test for balance with gentle lateral 322 CLINICAL DENTAL PROSTHETICS and protrusive movements. With the teeth in a lateral position of occlusion, insert the point of a wax knife between the teeth on the balancing side, and attempt to separate them; if they do separate, it shows that the occlusion of the teeth on that side is apparent only and is resulting from the displacement of the denture bases from the ridges. The cause of this error may be due either to an incorrect facc-bow reading, or to an incorrect condylar path registration. When the error is con- siderable, these registrations must be taken again, the models re-mounted on the articulator and the teeth re-set; but if the error is only slight, it may be corrected by grinding the occlusal surfaces of the teeth when the dentures are finished. Minor errors of cuspal interference may be eliminated at this stage, or when the dentures have been finished and fitted, by careful grinding of the teeth concerned. (d) Appearance This aspect of the try-in is a matter more for individual judgment and the patient’s ideas than for set rules. Certain things require to be checked, however, as routine. They arc; (i) Centre Line. - Stand in front of the patient, some distance away ; a wrong centre line will be obvious, but if in doubt any of the aids described in Chapter VI may be applied. (ii) Anterior Plane. - This may be observed from the same position and any tendency for this plane to slope markedly up or down should be noted and corrected ( see fig. 249). TRYING IN THE DENTURES 32S (iii) Shape of the Teeth. — Ensure that the selected teet'i con form with the patient’s facial type (see Chapter VII), and invariably consult the patient, to whom a mirror has been handed. (iv) Size of the Teeth. ~ Individual judgment must be relied on here together with the patient’s opinion. (v) Shade of the Teeth ( see chapter on Tooth Selection). (vi) Profile. - Observe the patient’s profile and note if the lips are either excessively distended or unduly sunken. In the first case, remove some wax from the labial flange and try the dentures in again. If this produces insufficient improsement, examine the denture to see if the teeth can be set farther in, or if smaller teeth can be used. If this is not possible, the six front teeth may need to be set to the gum. If the lips are sunken, build up wax on the labial flange, especially in the canine and premolar regions, until the profile is correct, and in some cases set the anterior teeth further forward. (vii) Amount of Tooth Visible. - Ask the patient to say ‘Yes’, and smile, and note how much tooth shows. Consider whether you like it or not. In this connexion remember that a smiling person usually only shows the upper teeth; if much of the lower incisors are visible, or only the lowers show, examine the amount of overbite and, if excessive, reduce it by lowering the mandibular teeth. If this does not effect an improvement, the height of the occlusal plane may icquirc to be altered. (viii) Regularity of the Teeth. - Few natural dentitions exhibit perfection, and to perfect a set-up in the incisor region, especially in persons of middle age, tends to emphasize that the teeth are artificial, therefore a little irregularity is usually desirable. Some common types of irregular set-up are illus- trated in the following diagrams (see figs. 250, 251 and 252). If the patient already has dentures and likes the appearance of them, copy them, since it is always inadvisable to alter a patient’s appearance radically, without his consent. (e) Approval of Appearance by the Patient It is always wise for the operator to obtain the patient s approval of the appearance of the waxed-up dentures before 324 CLINICAL DENTAL PROSTHETICS Fro. 250 Fic 231 OJfflO He. 232 they arc passed to the technician for completion, as this enables the operator to make necessary adjustments. Some patients arc quite prepared to leave the question of appearance to the operator, whilst others are extremely fussy over the smallest detail. When dealing with the former class, the operator should insist that they consider the matter of their appearance, other- wise when the dentures are finished they may react unfavour- ably. In the case of the fussy patient, much time and trouble must be spent on getting the shade, shape and set-up of the teeth just as the patient wishes. (It is \ery important to obtain his final approval before finishing the case.) In this connexion the operator often needs to use his restraining influence to avoid extremely bad errors of aesthetics, and a waste of time. It TRYING IN THE DENTURES 325 should be remembered that other people will see more of a patient’s dentures than he will, and if they are not aesthetically pleasing in the opinion of his relations and friends he will usually become dissatisfied with them. It is, therefore, advisable to ask the patient to bring a relation or candid friend with him at the time of trying-in the dentures, and the approval or criticism of this second individual should be sought as well as that of the patient himself. Chapter XII FITTING THE FINISHED DENTURES Examination* of the Finished Dentures Before fitting the dentures they should be inspected to ensure that they have been correctly finished by the technician, the following points being most important: 1. The fitting surface must show* no irregularities which are not present in the mouth. The commonest defects arise from a cut or scratch on the model, or air bubbles present in the plaster model. Both faults result in an excrescence on the fitting surface which should have been removed by the technician. 2. The entire periphery should be rounded and highly polished except the back-edge of the upper denture and the posterior lingual flange of the lower which should be thinned down almost to a knife-edge; but perfectly smooth and not sharp. 3. The edges of the relief area should be rounded and not left square and sharp {see fig. 253). FITTING THE FINISHED DENTURES 33- Placc the dentures, which have pre\ iously Jain in tepid water, in the mouth and examine them a^ for the try-in. Ten the retention of the upper by placing a finger behind the incisor teeth bringing pressure to bear in an outward and up- ward direction. If the back-edge of the denture has been correctly placed, considerable force should be needed to break the peripheral seal. The retention will increase after the patient has worn the dentures for a few days, due to the adaptation of the soft tissues to the denture. Checking the Occlusion If the try-in has been done carefully, the occlusion should be almost perfect. Slight unevenness often occurs, however, due to processing errors, and so the occlusion should be checked with articulating paper; this is paper impregnated with a blue dye. Place a piece between the teeth and ask the patient to then up and down in centric occlusion. Rcmo\c the dentures from the mouth and examine them. The occlusal surfaces will exhibit areas of blue coloration where the cusps and fossae of the opposing teeth have been in contact. These blue areas should be evenly spread over the occlusal surface, and the coloration of them should be uniform. Areas of hard or uneven pressure will show- up as darker, and broader, blue spots; areas of low pressure, or no contact at all, as very light!) coloured spots, or not coloured at all. To equalize the pressure, the high spots should he lightly ground with a carborundum stone. The denture should then be washed to remove the d\c and a further test with articulating paper made, and so on until occlusal balance is obtained. The Use of U'ax Templates Articulating paper has the disadvantage that it will colour a tooth even if it only rubs lightly against it, and thus areas which arc not in occlusion are frequently marked. If this possibility is borne in mind, articulating paper can be very successfully used to adjust the occlusion of finished dentures. A more satisfactory way of adjusting die occlusion is by using wax templates. The technique of this is as follows: Two strips of pink wax 6 mm. wide, of either single or double 328 CLINICAL DENTAL PROSTHETICS thickness, are softened and laid one on either side of the lower denture on the occlusal surfaces of the posterior teeth. The denture is then inserted in the mouth and the patient instructed to chew up and down on the wax with slow deliberate move- ments. The lower denture is removed from the mouth, and the wax templates chilled in cold water and gently removed from the denture. If these templates are then viewed by transmitted light, those areas where the occlusion is hard will be seen as thinned, completely transparent wax; or even as a hole right through the wax. Replacement of the template on the denture will enable the exact area of the tooth which requires grinding to be observed. Another advantage of the templates is that, by fitting the upper and lower dentures into their correct positions in one template, the actual position of occlusion on the opposite side of the dentures, as it exists in the mouth, may be observed, and gross errors readily seen. It requires to be emphasized that the even adjustment of the occlusion is most important to the success of the dentures, as uneven occlusion may cause soreness on the ridge, or in the sulcus, in its immediate vicinity. This should not be over- looked if a patient returns complaining of pain, because fre- quently the periphery of a denture is blamed for what is in reality a fault of occlusion. Uneven occlusion %vill also increase the patient’s difficulties when attempting to eat with the new dentures because they will feel uneven and uncomfortable when in occlusion. To achieve perfection of occlusion a check record should be taken, the dentures remounted on the articulator and the occlusion ground in as described in Chapter XIII. Fittinc Anatomically Articulated Dentures Check as for the try in. Test the articulation in centric, lateral, and protrusive relations with articulating paper and carry out a check record. At the second visit, when the dentures have had time to settle, the teeth should be ground in, in the mouth, using a carborundum powder in wax, or carborundum powder mixed with tooth-paste. Place a strip of carborundum wax FITTING THE FINISHED DENTURES 329 between the teeth and ask the patient to chew, until satisfied that the articulation is even. Although the wax holds the carborundum powder firmly, it is important to caution your patient not to swallow when grinding in the dentures as carborundum powder in the stomach is an irritant. This is specially important if tooth-paste is used as the vehicle. Finished Dentures Exhibiting an Incorrect Centric Occlusion If the centric occlusion is discovered to be incorrect at the finished stage, as will occasionally occur in spite of the greatest care being taken at the try-in stage, it may be due to a slight retrusion of the mandible, i.c. the dentures have been made to a slightly forward position. If this is not more than a { cusp it may be corrected by means of a check record ( see Chapter XIII). When the error is gross it will require the removal of all the posterior teeth from the lower denture as follows: Gently flame the posterior teeth of the lower demure, playing the flame actually on to the porcelain and not the acrylic base; conduction of the heat through the porcelain softens the acrylic without burning it, and the teeth may be prised off the denture. Wax blocks are then built to replace the teeth, trimmed to the correct height by trial, and the centric occlusion re-taken. The dentures are then re-articulated, and the back teeth re-set. If the over-jet resulting from the new record is abnormal, the lower front teeth must also be removed from the denture and re-set. If acrylic posterior teeth were used they are merely ground down and replaced ivith wax blocks for the new registration. In most cases of gross error the denture needs to be completely re-made. Attrition of the Front Teeth to Improve the Appearance When the upper and lower incisors erupt, the incisal edges present three small tubercles as shown in fig. 254. As the teeth come into use for incising, these tubercles are gradually worn away by the grinding of the lower teeth against the upper. This attrition results, firstly, in the formation of an even incisive edge, then, as age advances, this edge becomes irregular, due to 328 CLINICAL DENTAL PROSTHETICS thickness, are softened and laid one on either side of the lower denture on the occlusal surfaces of the posterior teeth. The denture is then inserted in the mouth and the patient instructed to chew up and down on the wax with slow deliberate move* ments. The lower denture is removed from the mouth, and the wax templates chilled in cold water and gently removed from the denture. If these templates are then viewed by transmitted light, those areas where the occlusion is hard will be seen as thinned, completely transparent wax; or even as a hole right through the wax. Replacement of the template on the denture will enable the exact area of the tooth which requires grinding to be observed. Another advantage of the templates is that, by fitting the upper and lower dentures into their correct positions in one template, the actual position of occlusion on the opposite side of the dentures, as it exists in the mouth, may be observed, and gross errors readily seen. It requires to be emphasized that the even adjustment of the occlusion is most important to the success of the dentures, as uneven occlusion may cause soreness on the ridge, or in the sulcus, in its immediate vicinity. This should not be over- looked if a patient returns complaining of pain, because fre- quently the periphery of a denture is blamed for what is in reality a fault of occlusion. Uneven occlusion will also increase the patient’s difficulties when attempting to eat with the new dentures because they will feel uneven and uncomfortable when in occlusion. To achieve perfection of occlusion a check record should be taken, the dentures remounted on the articulator and the occlusion ground in as described in Chapter XIII. Fitting Anatomically Articulated Dentures Check as for the try in. Test the articulation in centric, lateral, and protrusive relations with articulating paper and carry out a check record. At the second visit, when the dentures have had time to settle, the teeth should be ground in, in the mouth, using a carborundum powder in wax, or carborundum powder mixed with tooth-paste. Place a strip of carborundum wax FITTINC THE FINISHED DENTURES 329 between the teeth and ask. the patient to chew, until satisfied that the articulation is even. Although the wax holds the carborundum powder firmly, it is important to caution your patient not to swallow when grinding in the dentures as carborundum powder in the stomach is an irritant. This is specially important if tooth-paste is used as the vehicle. Finished Dentures Exhibiting an Incorrect Centric Occlusion If the centric occlusion is discovered to be incorrect at »he finished stage, as will occasionally occur in spite of the greatest care being taken at the try-in stage, it may be due to a slight rctrusion of the mandible, i.e. the dentures have been made to a slightly forward position. If this is not more than a J cusp it may be corrected by means of a check record (see Chapter XIII). When the error is gross it will require the removal of all the posterior teeth from the lower denture as follows: Gently flame the posterior teeth of the lower denture, playing the flame actually on to the porcelain and not the acrylic base; conduction of the heat through the porcelain softens the acrylic without burning it, and the teeth may be prised off the denture. Wax blocks arc then built to replace the teeth, trimmed to the correct height by trial, and the centric occlusion rc-taken. The dentures are then re-articulated, and the back teeth re-set. If the over-jet resulting from the new record is abnormal, the lower front teeth must also be removed from the denture and rc-set. If acrylic posterior teeth were used they arc merely ground down and replaced with wax blocks for the new registration. In most cases of gross error the denture needs to be completely re-made. Attrition of the Front Teeth to Improve the Appearance When the upper and lower incisors erupt, the incisal edges present three small tubercles as shown in fig. 254. As the teeth come into use for incising, these tubercles are gradually svom away by the grinding of the lower teeth against the upper. This attrition results, firstly, in the formation of an even incisive edge, then, as age advances, this edge becomes irregular, due to 33 ° CLINICAL DENTAL PROSTHETICS (a) Illustrating the alteration which occurs in the form ol of the incisive edge of an upper central incisoras the ) ears advance. (») Illustrates the shape of the incisive edges of the newly erupted front teeth and (c) shows how they wear by attrition. Close study will reveal how the pattern develops Fig. 354 uneven wear, and sometimes assumes a chisel-like form when viewed from the side. Many artificial teeth, as supplied, present a regular, even edge and if no attempt is made to simulate the wear of the natural teeth they appear obviously false. A little judicious FITTING THE FINISHED DENTURES 33I grinding of the incisive edges of the teeth with a carborundum stone makes a remarkable difference and enhances the natural appearance of the dentures. This should only be done, however, with the patient’s approval. The older the patient the greater will be the effects of attrition — therefore the attrition seen in a man of 70 should not be copied on dentures for a girl of 2 1 . The observation of people who possess their own teeth will disclose much about the wear of the incisive edge and the irregularity of the appearance. While on the subject of appearance, a few words on the reflection of light from the labial surface of the teeth may be useful. Examination of the labial surface of a natural incisor will disclose that two vertical grooves separate three ridges: the canines usually have one ridge separating two depressions. The rest of the surface, although smooth, is not regularly con- toured, being built up from a large number of facets. All these irregularities result in the incident rays of light which strike the tooth surface being, in the main, scattered as they are reflected, and only one or two of the more prominent ridges reflect light evenly as highspots. If artificial teeth are to appear natural therefore, they must scatter the incident rays, and here again the breaking up of the surface of the tooth by judicious grinding, followed by gentle polishing, can considerably enhance the appearance. Instructions to the Patient Many patients will have had experience with full dentures and may thus not require an explanation of the points about to be considered, but those patients having dentures fitted for the first time will need, and benefit by, information concerning the following: 1 . Wearing Dentures at Night Dentures invariably occupy more space in the mouth than did the natural teeth which they replace, and to begin with, the patient will be extremely conscious of their presence. Therefore, in order to reduce this period of discomfort to a minimum, it should be suggested that the dentures be worn at night, thus allowing the tongue, checks and lips to become FITTING THE FINISHED DENTURES 333 has to control the lower denture as well as the /ood. The following suggestions may be of some help during the tedious period of learning to eat. (a) The food should be cut into small pieces and only a little placed in the mouth at a time. (b) Commence by chewing in the premolar region on one or both sides; the latter causing the least instability. (c) The soft and non-stick)’ foods are easier to eat than the more fibrous types. (d) Chewing with the posterior teeth should be mastered before any attempt is made to bite with the incisors. 4. Talking People who have been edentulous for a considerable period will have adapted themselves to the prevailing conditions, and probably will have corrected any speech defects arising from the loss of the teeth. With the insertion of dentures, the condi- tions are suddenly changed and the tongue is conscious of the reduction of space, and may be cramped temporarily by tl.c bulk of the lingual flange of the lower denture. This may lead to difficulty in forming some of the speech sounds until the tongue has had sufficient time to adapt itself. Patients who are likely to experience speech difficulties should be advised •to read aloud, and practise any word which causes trouble. A few hours spent in this manner will enable most patients to speak naturally and with complete ease. Easing the Dentures With the fitting of correctly constructed dentures, and instruc- tions to the patient, the prosthetist’s part in the rehabilitation is almost complete for, except for minor adjustments of the peripheries and occlusion, it is now the patients perseverance and ability to learn to use the dentures which decide the final success of the case. The patient should be asked to attend for examination forty-eight hours after the insertion of the dentures so that the prosthetist may carry out any necessary adjustments. Soreness may occur in that time due to the fact that functional trimming of the peripheries at the impression stage rarely reproduces all the functional movements, and when the dentures are first worn there is probably slight over- 334 CLINICAL DENTAL PROSTHETICS extension somewhere. The flange of the denture is thus too deep and presses into the tissues of the sulcus, forming first an angry red line, which later breaks down into an ulcer, the depth and extent of which depends on the degree of over- extension of the denture base. Also, in that time, the dentures will have settled with possible slight changes in the evenness of occlusion. The overextended flange must be trimmed and the occlusion ground in. A further visit may be necessary for final corrections, as it is never wise to remove too much of the periphery- at one stage, since over-easing may lead to a leak in the peripheral seal. Other causes of soreness, and the complaints made by patients, are dealt with in the next chapter. If, after being worn for a short time, the dentures hurt, they should not be discarded immediately, unless the pain is severe, since perseverance will often overcome slight soreness. If the dentures have to be left out because of pain, they should be worn for a few hours immediately before visiting the dental surgeon because, unless this is done, there probably will be no mark in the mouth to indicate where the denture is over- extended. The technique of easing: It is essential to locate exactly which area of the denture base is overextended. Sometimes this can be done visually, but frequently the ulcer cannot be seen when the denture is in place. In these instances a mark must be made on the tissues, which will transfer itself to the denture base in the vicinity of the ulcer. Such a mark can be made with either zinc oxide paste, tooth-paste, or indelible pencil. The tissues are dried, a little paste is placed on the'sore area with a probe, or a mark is made with a wet indelible pencil, the denture is then inserted and pressed gently but firmly into place. When it is removed the paste, or some of the indelible material, will ha\e transferred itself to the denture base. A better method, and one which can be employed even before an ulcer has developed, if, when fitting the denture one suspects that it is overextended anywhere, is to coat the area of the periphery- or fitting surface in question with a paste of equal parts of zinc oxide, starch and lanoline, so thickly that the acrylic cannot be seen through the paste and then insert the • trp ffv FITTING THE FINISHED DENTURES 33^. denture. The patient is then instructed to chew, swal/ow-a'nd. move the lips and checks because pressure points frequently develop only in function. The denture is then removed and if overextension exists it will be readily visible as an area of acrylic completely un- covered by the paste (see fig. 255). This area of the denture is Tig. 255. -Area of overextension has been coated with easing paste and this has been squeezed away in area ofhard pressure (arrowed). then trimmed with a stone or file, highly polished and the denture reinserted. In cases of gross overextension resulting in severe ulceration, the patient should be instructed to leave the denture out for twenty-four hours in order to allow the swelling to subside, otherwise the denture will require to be over- trimmed and this may reduce its retention. When easing it should always be remembered that soreness and ulceration of the tissues is frequently caused by un- balanced occlusion, or cuspal interference, causing excessive pressure to be applied to the tissues under the denture base. It is therefore sound practice always to check the occlusion when casing a denture. CHAPTER XIII CHECK RECORDS FOR COMPLETED DENTURES A. Dentures Constructed using an Adjustable Type Articulator The efficiency and comfort that a patient experiences when using full dentures depends to a large extent on the harmony of the occlusion. A suitable impression technique, carefully carried out, will result in dentures which arc stable provided that there is no overextension and that the polished surfaces arc correctly shaped. With care the correct position of centric occlusion may be obtained and if an adjustable articulator is used in conjunc- tion with a face-bow and lateral occlusal records a satisfactory balanced articulation will be produced. This, then, should result in comfortable and efficient dentures with an harmonious occlusion and articulation; unfortunately, however, faults occur during the construction of dentures which result in errors in the occlusion that are indctectable when the dentures are examined in the mouth (fig. 256). These faults may be clearly seen however when the dentures are mounted in an articulator after centric check records ha\e been taken (fig. 257). Such dentures may cause discomfort to the wearer and result in reduced efficiency unless the faults of occlusion are rectified. The errors which occur are due to one, or a combina- tion of the following: (1) Incorrect registration of centric occlusion. (2) Irregularities in setting the teeth. (3) Tooth movement when flashing and packing. (4} Incomplete flask closure. (5) Wear in moving parts of the articulator. ( 1 ) Incorrect Registration of Centric Occlusion.- This is probably the most common cause of error in the occlusion of finished dentures. When registering the position of centric occlusion considerable 33 6 CHECK RECORDS FOR COMPLETED DENTURES 337 338 CLINICAL DENTAL PROSTHETICS CHECK RECORDS FOR COMPLETED DENTURES 339 care is taken to obtain a correct vertical dimension and the physiological fully rctruded position of the mandible, but often the record rims when brought together exert uneven pressure on their respective supporting alveolar ridges, and this condition passes unnoticed. The uneven pressure may be due to premature contact of the record rims on one side of the mouth, in the second molar region of both sides, or in the incisor region. This causes uneven compression of the mucosa support- ing the record blocks and often displaces them from the ridges in areas away from the region of premature contact. When the plaster models are placed in the record blocks obviously no such compression or displacement occurs and therefore the occlusion as registered in the articulator differs from that registered in the mouth. Thus an error in occlusion has been established which possibly may be passed over at the try-in stage due to the poor fit of the trial denture bases allowing movement to take place. On finishing the denture the teeth are found to occlude only in the area where the premature contact of the record rims occurred, the remainder of the teeth being slightly out of contact (see fig. 257). The degree of separation will be related to the degree of premature contact occurring between the record rims. This will vary from the almost indiscernible (see fig. 256) to a stage when a wax knife blade may be inserted between the un-occluding teeth. Another fault causing errors in the occlusion of the finished dentures results from slight movement of record blocks on the ridges during centric registration due to their imperfect fit and inadequate retention. The position of centric occlusion of the finished dentures will be slightly inaccurate for this reason and the dentures will tend to move on the ridges as the cuspal inclines or the teeth guide the dentures into their slightly inaccurate position of occlusion when the mandible assumes its correct centric relationship with the maxilla. This continual denture movement during mastication causes sore- ness of the ridge; usually the lower since this denture is the more unstable of the two. Finally, an error of occlusion may result from the manner in which the models and record blocks are set in the articulator. The models may not be placed accurately in the blocks, 340 CLINICAL DENTAL PROSTHETICS or the articulator may not be handled with due care when the models are being attached with plaster. All the forementioned errors may be of a minor nature and can usually be avoided by using an accurately fitting acrylic base in preference to the shellac type of base which invariably warps slightly. The minor errors only cause slight discrepancies in the occlusion of the teeth and will probably pass unnoticed at the try-in stage, and often in the finished denture stage, and are observed only when carrying out a centric check record {see figs. 256 and 257). {2) Irregularities In Setting the Teeth. — The technician when setting up teeth is unlikely to produce a perfectly even contact in centric and lateral occlusions, some teeth will be in good occlusion whilst others will be slightly out of occlusion, tints producing areas of heavy' pressure. Also, when setting and testing the occlusion for lateral slide the teeth being held in wax, which exhibits a certain amount of resiliency', permits tooth movement to occur when hard occlusal contact areas are encountered. This cannot happen when the teeth are held firmly in the final denture base material and results in areas of premature tooth contact in the occlusion and articulation of the finished dentures. In waxing up following the setting of teeth it is possible for them to move slightly due to the contraction of the w-ax on cooling, causing irregularities in the articulation and occlusion of completed dentures. These possibilities point to the need for a final adjustment of occlusion once the dentures are finished. (3) Tooth Movement when Flashing and Packing. - Movement of the teeth may occur at the time of boiling out the wax trial base after the dentures have been flasked and if such teeth are not correctly repositioned they will cause minor occlusal irregularities. Also, when packing, teeth may be driven into the enveloping plaster, particularly when packing follows soon after investing and the plaster is in the ‘green state’. The possibility of such an error occurring is increased when the methyl methacrylate is used in a slightly advanced stage of dough, and when the posterior teeth have been ground to fit CHECK RECORDS FOR COMPLETED DENTURES 3 1 1 close to the ridge. Rapid closure of the flask in the press trill add to the hazard. (4) Incomplete Flask Closure. — Such an occurrence not only causes an increase of vertical dimension but also results in an upset of balanced occlusion. (5) Articulator Wear. - All articulators are subjert to w ear and the older and more worn the articulator the greater will be the errors in occlusion and articulation. Every piece of mechanical apparatus exhibits some play in its moving parts and when this becomes easily detectable the bearing should be replaced. It can be appreciated that even with care on the part of the surgeon and technician slight errors may occur which influence the final occlusion and articulation of finished dentures. These errors in some instances may be corrected by careful use of articulating paper at the chairsidc but such correction is often proved false when check bites arc taken for confirmation. It is far more satisfactory and often less time consuming, clinically, to register the position of centric occlusion again, this time using the finished dentures as the bite blocks; take a face-bow reading and lateral records, set the finished dentures in an adjustable type of articulator and grind-in the occlusion. The following arc details of the procedure: (]) Registration of Centric Relationship without Tooth Contact. - The upper denture is seated in position in the mouth. A sheet of pink wax is thoroughly softened in the bunsen flame and two half-inch wide strips of double thickness, and of sufficient length to cover the prcmolar and molar teeth of both sides, arc laid on the occlusal surface of the lower denture (fig. 258). Whilst the wax is still very soft the denture is seated in the mouth and the patient requested to close in the retruded posi- tion (Chapter VI) until the teeth arc almost in occlusion. Tins can be judged by observing the separation of upper and lower incisors (fig. 259). The wax templates arc chilled in the mouth with a cold water jet and removed and placed on one side whilst a second registration is carried out. It is advisable to take two sets of templates so that one may be used as a check of the other when the dentures have been set in the articulator. 342 CLINICAL DENTAL PROSTHETICS Fio. 258 - Soft wax strips placed on the occlusal surfaces of the posterior teeth. Fie. 259 - Centric relationship recorded using vers' soft v ax. Mandibular closure is stopped before posterior tooth contact occurs; this position must fall within the limits of the free- was space. CHECK RECORDS FOR COMPLETED DENTURES 343 Any discrepancy between the two sets of tempiates necessitates further centric readings. The wax should be as soft as possible when the lower denture is placed in the mouth in order to minimize compression of the mucosa supporting the dentures. Plaster of Paris may be used as an alternative to wax. It is extremely important when securing this position of centric relation between the mandible and maxilla that the teeth are not allowed to make contact, for if tooth contact does Occur the lower cusps by moving along the cuspal inclines of the upper teeth may guide the mandible into the position of occlusion to which the dentures were constricted and thus, if an error exists, prevent the desired correction of maxillo- mandibular relationship. (2) Lateral or Protrusive Records . - A strip of softened wax of double thickness is placed on the occlusal surface of the lower denture, the denture placed in the mouth and the mandible moved to the right lateral position and closed almost to tooth contact. A second template records the left lateral position (Chapter IX). If the patient experiences difficulty in making lateral movements then a single protrusive record should be taken with the mandible protruded approximately ^ in. These records are used to set the condylar guide paths of the adjustable articulator. (3) Face-bow Registration. — A treble thickness of softened pink wax is moulded around the prongs of the face-bow fork and the fork placed between the occlusal surfaces of the teeth with the arm of the fork projecting straight out but set to one side of the mid-line. The patient closes into the soft wax and holds the fork firmly in position whilst the face-bow is attached to the fork and related to the condylar heads (fig. 260). The reason for taking the face-bow* record is that it enables the technician to set the upper denture in the articulator frame in the same relationship to the hinge-axis of the articulator as the denture, when in the patient’s mouth, bears to the condylar axis of the mandible when the condyles are in the physiologic- ally fully retruded position in the fossse. By using the wax template recording the centric relation, Fig. 260 (a) Lateral view of face-bow. The condvlar cups are posi- tioned on a line from the outer canthus of the e>e to the top of the externat auditory meatus and t cm. in ront of the latter. {b) Front view. The fork of ibe face-bow positioned to one side of the midline to facilitate mounting in the articulator. CHECK RECORDS FOR COMPLETED DENTURES 345 previously taken, the lower denture can also be positioned in the articulator frame in a relationship to the hinge axis of the articulator which is identical to the lower denture’s relation- ship to the condylar axis when the denture is in the mouth. The relationship of the upper and lower dentures to the hinge axis, both human and mechanical, arc thus identical. There- fore, provided that it is accepted that movement through the free-way Space is a pure hinge type movement it is now possible to close the articulator frame, within the limits of the free-way space, with the knowledge that both the paths of closure of the articulator and the mandible will be the same. If the thickness of the wax template recording centric relation is not in excess of the free-way space then it can be removed from between the dentures when in the articulator and the teeth closed together to show their true relationship since the human and mechanical paths of closure will be the same in each case. (4) Mounting the Dentures in an Adjustable Articulator. - The face- bow, with the upper denture secured to the fork, is adjusted on the articulator (Chapter IX) and the denture attached to the upper arm of the articulator with plaster of Paris; the under- cuts of the fitting surface of the denture ha\ing previously been blocked out with wax or plasticine (fig. 26 r). After the face-bow has been removed the lower denture is attached to the upper denture by means of one set of wax tem- plates recording the centric relation and in this position the lower denture is secured to the lower arm of the articulator (fig. 262). When the plaster has set the wax templates are removed from the dentures and the wax templates recording the lateral, or protrusive, positions of the mandible substituted in order to set the condylar guides of the articulator (Chapter IX). Once the condylar guidance has been set the wax template of centric relation is repositioned between the teeth and the locking nut of the incisal guide pin tightened, after which the template can be removed and the teeth examined to ascertain whether or not there is contact between the upper and lower teeth which would indicate that the patient had He. 2G2. - Centric relationship record used lo mount the lower denture in the articulator closed too firmly into the wax template during the recording of the centric relation (fig. 263). If the wax record is satisfactory and no tooth contact occurs then the incisal guide pin may be removed and the articulator closed until the teeth occlude and the occlusion studied for points of premature contact or change in maxillo-mandibuiar relationship (fig. 264). Figs. 265 and 266 illustrate two cases of corrected centric relationships associated with areas of premature tootli contact obtained by check records, and their appearance after grinding- in the occlusion. (5) Correcting the Occlusion by Spot Grinding. - In order to produce a satisfactory' result it is important to carry out the grinding systematically to ensure that: A. The vertical dimension is maintained. B. An even distribution of occlusal stress is obtained in centric occlusion. C. An even distribution of stress is maintained in lateral Tig. 263(a) and (6). - 1 lie centric relationship record luj been removed, after locking the incisal guide pin, tn show the relation between the upper and lower denture*. Note that no oecluwl contact was made during the rentric check record registration, and that there appears to be greater separation between the upper and lower teeth on the right side than on the left. Alto on the left side there appear* to be slight retrusfon of the mandible judged bj the cuspal relauonship of the opposing teeth. w Fir. 264 - The incisal guide pin has lwrn removed and die articulator closed to give tooth Contact Right and left side, and front views are shown. Tooth contact occurs on the left side whilst the nghl side shows Jack of contact. The vertical dimension is controlled by the loner bttcc.il cusps and the upper palatal cusps and their opposing fossae, tliercfore it is essential that these z ones must receive careful consideration when establishing centric and lateral occlusions. Grinding in to Centnc Occlusion. — Place thin blue articulating paper on the occlusal surface of the lower teeth and close the articulator with sufficient pressure to record just the first con- tact areas (fig. 267). Observe the prominent cusp or cusps and decide whether the cusp or its opposing fossa should be ground by checking this cusp in its lateral working position and then its balancing position. If the offending cusp makes premature contact in both centric and lateral positions then the cusp, and not the fossa, should be ground to produce even centric occlusion (fig. 268). When, however, a cusp producing prema- ture contact in the centric position docs not cause premature contact when in working and balancing positions then the CHECK RECORDS FOR COMPLETED DENTURES 35J I'm. aG 1 Fig. 265 -Thu case, mounted in an articulator following check records, shows premature contact points in the premolar area of both sides with slight re tension of the mandible (<») and (A). By careful grinding an e\en occlusion is obtained CO «“>d (0- Fig 266. — This case, mounted in an articulator following check records, shows premature contact in the premoiar region of both sides with marked reimsion of the mandible ( occlusion in 35 area and the complete lack of contact on the opposite side. fossa is ground to accommodate the cusp (fig. 269). (The lateral contacts can be marked with red articulating paper for purposes of differentiation.) This principle is followed until an even centric occlusion is obtained throughout the dentition. Grinding-in for Lateral Excursions. — To enhance the retention and stability of the dentures and to reduce the stress applied to the alveolar ridges as the mandible moves laterally it is most important to pro\idc a free sliding lateral articulation and elimination of cusp lock. Red articulating paper is placed between the occlusal sur- faces of the teeth, and the dentures moved with light picssurc from centric occlusion into right lateral occlusion. If the upper and lower buccal cusps make premature contact and the balancing side is out of occlusion then the upper buccal cusp is ground (fig. 270) as the lower buccal cusp is required to main- tain vertical dimension and even pressure in centric occlusion. 35 ^ CLINICAL DENTAL PROSTHETICS Fig. 268. - : . The lower right buccal cusp occludes prema- turely in centric occlusion 2. When tested as a working side contact it is found to be in premature occlusion, as is the case, also, when tested as a balancing side contact. 3. Therefore the lower buccal cusp is ground to produce even contact in centric occlusion. 4 Compare with fig. 269 When the lower lingual and upper palatal cusps occlude prematurely in this lateral position the lower lingual cusp is ground to produce balance of both sides of the denture (fig. 271) ; the upper palatal cusp being required for the main- tenance of vertical dimension in centric occlusion. The grinding of the Buccal Upper and Lingual Lower cusps to produce balance in lateral movements is often referred to as grinding to the BULL rule. Should the balancing side exhibit premature occlusion between the lower buccal cusp and the palatal upper cusp it CHECK RECORDS FOR COMPLETED DENTURES 357 Fic. 269 - 1 . The lower right buccal cusp occludes prema- turely in centric occlusion. 1 . When tested as a working side contact occlusion of the teeth on the balancing side occurs 3. If the lower nght buccal cusp is checked in its balancing side contact it would be observed that the working side (left) also shows tooth contact. Therefore the fossa of the upper right tooth sliould be deepened to produce even contact in centric occlusion 4. Contrast with fig. 268. The checking and grinding is earned out in stages and it may be necessary to gnnd tooth fossa and cusp in order to produce the desired balance in centric and eccentric occlusions. will be necessary to grind the palatal upper cusp and not the lower buccal cusp since this cusp is required to maintain vertical dimension and even pressure in centric occlusion and contact in the working lateral position. The procedure having been completed for the right lateral position it is then repeated for the left lateral excursion. 358 CLINICAL DENTAL PROSTHETICS s 4 . Fig. 270.-3 The upper right buccal cusp is seen lo be in premature contact when the right side is acting as the working side. 3. The upper buccal cusp is reduced to bring the teeth on the balancing side into occlusion. 3 This does not alter the evenness of centric occlusion, 1 and 4 Having established a free lateral sliding movement of the occlusion of the protrusive contacts are studied. Correction of Premature Contacts in Protrusion. — As we are dealing with an artificial dentition, and are not concerned with the possible over-eruption of teeth as may occur with a natural dentition, most of the grinding for correction of premature contacts of incisal edges of anterior teeth, when in protrusive occlusion, can be carried out at the expense of the lower incisors (fig. 272). A limited amount of grinding, however, of the upper anterior teeth to simulate attrition, related to the patient’s age, can enhance the appearance of the dentures. CHECK RECORDS FOR COMPLETED DENTURES 359 Tic* 27 1 - i Tlic lingual cusp or the lower nqhl tooili occlude* prematurely when the nqhl side become* the workinq wde. In order to produce contact on the balancing side the linqual cusp must be reduced. 3, and not the upprr palatal cusp which is rrejtnrrd to maintain e\cn centric occlusion, 1 and 4. (G) Perfecting Articulation icith Grinding-in Paste. - The main correction of occlusal irregularities must be carried out with small mounted abrasive stones in a hand-piccc so that the vertical dimension is kept under control. The amount of adjustment, made with grinding-in paste, must be small as this will reduce all occluding surfaces and if excessive will result in loss of vertical dimension. A paste of coarse grit carborundum powder mixed with vaseline or tooth paste is used first, followed by one of fine grit carborundum to smooth the previously ground tooth surfaces and produce a perfectly even occlusion 360 CLINICAL DENTAL PROSTHETICS I 2 . tfWV 3 . 4 . Tic 37®. - If, when in protrusion, the incisors meet edge to edge, 2, with the posterior teeth out of occlusion the lower incisors may he ground to restore posterior contact, 3. This will reduce the oserbilc and usually increase the oseijet but cause no change in the c\en contact of the posterior teeth in centric occlusion, 1 and 4. This should not be done when dealing with natural dentitions as further eruption of the lower an tenors may occur to restore contact with the upper incisors. In this instance some reduction of the incisal edge of the upper incisors together with an increase in its palato-labial slope will help Excessise grinding should be asoided as the appearance may be spoiled. Fm. 273(a) CHECK RECORDS FOR COMPLETED DENTURES 361 (fig. 273(0) and (6)). A final grinding-in of the occlusion may take place in the mouth when the dentures are returned to the patient if it is considered desirable, but if carried out it should be for a very limited period as the patient may make lateral excursions with some degree of protrusion which mil disturb the previously arranged articulation, and long periods of grind- ing mil close the vertical dimension further. When using the paste, either with the articulator or in the mouth, it is placed on the occlusal surface of the lower denture and lateral movements are made with the teeth maintaining contact. Movement is continued until such time as a free sliding articulation results. A warning must be given to the patient not to swallow whilst the carborundum paste is in the mouth, rest periods must be given to allow accumulated saliva to be rinsed away. (7) Reduction of Sharp Edges of Ground Teeth. - On the comple- tion of all grinding, sharp edges occurring buccally and lingually must be rounded to prevent tongue and cheek irrita- tion. Rubber wheels, Water of Ayr stone, and finally pumice paste used with polishing brushes will produce a smooth finish. The patient now has harmonious occlusion and articulation (fig. 273 (c), ( i) and (.)), B. Dentures Constructed in a Plane Line Articulator The same check record technique should be used with dentures set in a plane line articulator and although it is not possible in every case to produce a completely free sliding occlusion in the anterior region, excellent results are obtained for a very large majority of patients. The depth of overbite, however, in a few cases restricts the free sliding movement and can only be eliminated by the mutilation of the appearance. Nevertheless, if, when the teeth are being set up, a minimum overbite of the anterior teeth is employed with an equal overjet, and compen- sating curves arc introduced there should be no difficulty in establishing a sliding articulation free from cusp lock. Even where the depth of overbite restricts lateral movements it is possible to proride a reduction of cusp lock posteriorly and the technique has the considerable advantage of permitting correction of minor errors in centric occlusion and the estab- 3® 2 CLINICAL DENTAL PROSTHETIC « Tic. 273 — The dentures, seen m figs 256 and 257 have been gTound-m to produce an e\en occlusal contact The dentures seen in fig 2-3 ( 4 ) and (c) have been relumed to the patient and the right and left views show even contact in centric occlusion The front view illustrates the slight amount of grinding earned out on the upper incisors to simulate aunt ion. Compare with fig 286. 3lic sensitivity. Test is performed by strapping some filings from the suspected denture under gauze to the skin. Thts test is positive, note the duster of vesicles. 374 CLINICAL DENTAL PROSTHETICS with the dentures, appears slightly inflamed and bright red in colour. In most cases the irritation is confined to the tissues in contact with the unpolished surfaces of the dentures, though occasionally it also affects the cheeks, lips and tongue to a lesser degree. It may only affect the upper denture area, and is always less marked under the lower denture, owing to the thicker layer of intervening saliva. Treatment: New dentures must be constructed in another material. Fortunately there do not appear to be any recorded cases of an individual being allergic to both vulcanite and methyl methacrylate. (m) Rough Filling Surface If a denture has been processed on a poorly poured model, small pimples will be found on the fitting surface where the material has heen forced into the small air bubbles of the model. Normally these pimples arc removed by the technician, but if they are overlooked the patient will complain of pain under pressure and a local area of angry red irritation can be seen, usually in the palate. Treatment: Remove the ofTending roughness from the denture. (n) Infection with Monilia albicans The area of the palate which is damaged traumatically by the rough fitting surface of a denture frequently becomes second- arily infected, usually by one of the fungi — Monilia Albicans whose presence can be vertified by culturing a sw'ab from the tissues. Especially is this so if the patient lives on a low protein and vitamin diet and also wears the dentures at night or has had long continued anti-biotic therapy. The appearance of the palate is of an acute red inflammation terminating sharply at the borders of the denture. The mucous membrane will be swollen and smooth in early cases but in those of long standing will present a granular type of hyperplasia { see fig. 277). The treatment is to polish the fitting surface of the denture and instruct the patient to apply daily to the fitting surface for io days a fungicide such as Nystatin ointment or Fuchsonium. In severe cases Nystatin may be given systcmically. The patient should also be instructed to remove the denture at COMPLAINTS 375 FlO. 277. - Clt*« up of h>peiplasia of palate: compare >\tth f>S- 53- night without fail and place it in a dilute solution of hypo- chlorite such as Milton. During the acute phase the denture should not be worn during the day more than necessary. A hypochlorite mouthwash as hot as tolerable should also be used two or three times a day, the hot fluid being held in con- tact with the inflamed tissues as long as possible. The protein and vitamin content of the diet should be increased and the carbohydrate content reduced. This condition is difficult to treat, but perseverance with the above routine will, in several weeks, usually produce a very marked improvement. This condition is becoming common these days, probably as a result of the increasing use of alginate impression materials which copy on the model all the small surface details of the palatal tissues [see fig. 278). If such impression materials arc used the palatal surface of the model should be covered with 374 CLINICAL DENTAL PROSTHETICS with the dentures, appears slightly inflamed and bright red in colour. In most cases the irritation is confined to the tissues in contact with the unpolished surfaces of the dentures, though occasionally it also affects the cheeks, lips and tongue to a lesser degree. It may only affect the upper denture area, and is always less marked under the lower denture, owing to the thicker layer of intervening saliva. Treatment: New dentures must be constructed in another material. Fortunately there do not appear to be any recorded cases of an individual being allergic to both vulcanite and methyl methacrylate. (m) Rough Fitting Surf act If a denture has been processed on a poorly poured model, small pimples will be found on the fitting surface where the material has been forced into the small air bubbles of the model. Normally these pimples arc removed by the technician, but if they are overlooked the patient will complain of pain under pressure and a local area of angry’ red irritation can be seen, usually in the palate. Treatment: Remove the offending roughness from the denture. (n) Infection with Monilia albicans The area of the palate which is damaged traumaticallv by the rough fitting surface of a denture frequently becomes second- arily infected, usually by one of the fungi — Monilia Albicans whose presence can be vertified by culturing a swab from the tissues. Especially is this so if the patient lives on a low protein and vitamin diet and also wears the dentures at night or has had long continued anti-biotic therapy. The appearance of the palate is of an acute red inflammation terminating sharply at the borders of the denture. The mucous membrane will be swollen and smooth in early cases but in those of long standing will present a granular type of hyperplasia ( see fig. 277). The treatment is to polish the fitting surface of the denture and instruct the patient to apply daily to the fitting surface for 10 days a fungicide such as Nystatin ointment or Fuchsomurn. In severe cases Nystatin may be given systemically. Inc patient should also' be instructed to remove the denture at COMPLAINTS 375 Fig. 277. - Close up of hyperplasia of palate compare with f'S 53- night without fail and place it in a dilute solution of hypo- chlorite such as Milton. During the acute phase the denture should not be worn during the day more than necessary. A hypochlorite mouthwash as hot as tolerable should also be used two or three times a day, the hot fluid being held in con- tact with the inflamed tissues as long as possible. The protein and vitamin content of the diet should be increased and the carbohydrate content reduced. This condition is difficult to treat, but perseverance with the above routine will, in several weeks, usually produce a very marked improvement. This condition is becoming common these days, probably as a result of the increasing use of alginate impression materials which copy on the model all the small surface details of the palatal tissues fig. 278). If such impression materials arc used the palatal surface of the model should be covered with 376 CLINICAL DENTAL PROSTHETICS M « Fic. 27B. («) Coronal action throu<;li alginate imprrwion »lnn\inc the jftarp detail of the palate which it pnxlui-r*. ( 4 ) Silhouette of fittint; surface of denture made to a model nil from such an impression. thin tinfoil before the denture is processed so as io reduce its roughness. (0) Sit allotting and Sore Throat These two complaints arc listed together as they arc merely different ways of describing pain arising from a common cause, which is invariably the overextension of a well-fitting denture. The cause in the upper is extension on to the soft palate with firm pressure and good retention, or excessive pressure in the hamular notches, whilst in the lower it is over- extension distally in the lingual pouch. The pain erases if the COMPLAINTS 377 offending denture is left out, and starts again very soon after its reinsertion. Treatment: The patient will usually know which denture is at fault and examination of the regions described will show a slight redness. Reduction of the overextension is all that is required. (j>) Undercuts Sometimes an operator will make use of an undercut area which in his judgment is unlikely to cause pain, and although the new denture was inserted with comfort, the patient returns with the complaint that inserting and removing the denture is getting increasingly painful. The maximum bulge of the alveolus in this area is found to be red and painful, and in some cases ulcerated. Treatment: It may be possible to insert this side of the denture first, quite painlessly, and then the opposite side, removing it in reverse order. If this manoeuvring is not successful the fitting surface must be cut away until the denture can be in- serted comfortably but the periphery must not be reduced in height. Often the flange will be too thin to allow sufficient to be removed from the fitting surface and if this is so the flange must be thickened by the addition of more material. Should this easing ruin the retention, as is likely to be the case if much has to be cut away, an alveolectomy will be necessary followed by a new buccal or labial flange. This may cause warpage with an acrylic denture in which case a completely new denture will be the only remedy. 2. Appearance In spite of the greatest care on the part of the operator to obtain the patient’s full approval of his appearance at the ‘try-in’ stage, there will always be some patients who are dissatisfied with their appearance when wearing the finished dentures. The patient should not be condemned too severely for this inconsistency, as it is difficult to form a considered opinion on all details of facial appearance when sitting in a strange chair, under strange surroundings, with strange and bulky apparatus in the mouth, and being asked to criticize 37^ CLINICAL DENTAL PROSTHETICS the work or a professional man. The number of patients who are dissatisfied with their appearance with the final dentures can be much reduced if the operator insists on a relation or candid friend being present at the try-in stage. The number can be reduced even further if the patient is allowed to take the set-up dentures home for the criticism of his immediate circle of relations and friends. The risk of damage to these waxed-up dentures wall only be slight with the averagely intelli- gent individual, if it is explained to him that the teeth arc on!) mounted in wax, which will soften if worn in the mouth for more than three minutes without removal and hardening in cold water, and that nothing can be eaten or drunk whilst wearing them without their complete destruction. A man will quite often express his complete satisfaction with the finished dentures only to return rather sheepishly a few days later with the remark: ‘My wife says she does not like them, in fact she says they look dreadful.’ The following examples of complaints about appearance arc by no means comprehensive but will be found to co\cr the main points. (c) jYose and Chin Approximating This complaint may be made of new dentures, or of old ones, and is due to a so-called closed ‘bite,’ which term is synonymous with excessive free-way space. Treatment: As previously described for over closure. (£) Cheeks and Lips Falling In This is a condition which only arises after a patient has been edentulous for a number of years, and is due partly to the lack of tone of the facial muscles, and partly to the lack of support of them by the teeth and alveolar ridges. This support is mainly maxillary, where unfortunately the greatest ahcolar absorption is buccal and labial. Treatment: This consists of building out the upper denture, frequently to a greater extent than the original tissues, to compensate for the loss of muscular tone. This ‘plumping should be placed in the canine and prcmolar area, i.c. the region of the modiolus and not in the anterior region [see COMPLAINTS 379 fig. 279). In cases where the retention is really excellent, the teeth may be sct»up outside the Hdge, but this must not be excessive. Care must be taken w hen making these additions to the denture to retain a concavity directed outwards and downwards, to that the buccinators can support the denture upwards and inwards, otherwise the extra bulk will merch supply a ledge which will enable these muscles to pull the denture down. (c) Angular Cheilitis or Soreness of the Comers oj the Mouth As described previously this is frequently the rrsult of loss of vertical dimension and muscle tone and the comers of the mouth fall in and become bathed in saliva and develop fissures. Frequently however, as with traumatic damage to the palatr, a secondary infection with Momlta albicans supervenes, espvciallv if such an infection already exists in the mouth. In these cases treatment, such as that outlined on pages 373 and 374, should be instituted and at the same time the vertical dimension should be restored (but nc\cr opened) and the upper denture ‘plumped’ to help restore the muscle tone. COMPLAINTS 38t times expressed that moving the teeth anterior to the ridge, into the position the natural teeth occupied, will affect the stability of the denture, but this is not so. Stability will be jeopardized much more by encroaching on the tongue, than by setting the teeth in the neutral zone where pressures of tongue and lip arc equalized. A further point to be remembered is, that a patient who has been edentulous for a sufficient length of time for this degree of absorption to have taken place, will almost certainly ha\ - e been wearing dentures, and will have acquired a considerable degree of muscular control. Treatment: New dentures will almost certainly have to be made. If only the anterior teeth of the existing denture are moved forward, larger ones will be required if proximal contact is to be maintained, and this is contra-indicated if the teeth originally chosen were correct; if the teeth are to be moved back the converse is equally true. (e) Amount of Tooth Shotting This complaint is nearly always with regard to the upper antcriors, and will be that cither too much or too little tooth is showing. It must be remembered that the upper natural teeth show less in old age than in youth, owing to attrition and laxity of the lips. Treatment: Usually the dentures should be entirely re-made with the occlusal plane raised or lowered as the case may be, with longer or shorter anterior teeth if necessary. If the com- plaint is that too much tooth is showing, there is a temptation to grind away the offending portion, but this will ruin a balanced articulation since the patient will be unable to obtain incisive contact. (_/") General Dissatisfaction One of the most difficult cases with which a prosthetist may have to deal is that of the patient, fitted with new dentures, who returns a few days later with the vague remark that he 'does not like them’. He can specify no particular complaint .and it will be found on questioning that comfort, retention, stability and efficiency arc not at fault, so the conclusion, which is invariably right, is that it is a question of appearance. 3^0 CLINICAL DENTAL PROSTHETICS (d) Colour, Shape and Position 0/ Anterior Teeth Colour : This complaint is almost invariably that the teeth arc too dark or too yellow, but before changing them it must be explained to the patient that natural teeth darken with age and that very' light-shaded teeth look more artificial than darker ones. Treatment: Comply if possible with the patient’s request for lighter teeth, usually by a compromise between the shade chosen by the operator and that chosen by the patient. If the operator feels that a patient is insisting on such an unreasonably light shade that the dentures will look absurd, he may be well advised to refuse to replace the teeth by others which will damage his reputation as an artistic prosthetist. Shape: Few people arc sufficiently observant to be able to describe the shape of their lost teeth and arc likely to say vaguely, when referring to their dentures, that ‘they don’t look right’. This question of shape is closely bound up in that of apparent size, and a different make of tooth of the same basic shape and size may well look more natural. Artificial teeth usually look larger than natural teeth of identical size, probably because their mesial and distal surfaces arc not so rounded, and so the eye is able to focus on their width more accurately. Treatment: Remove the teeth complained of and replace them with others mounted in wax, until by a process of trial and error mutually suitable ones are obtained, which are then permanently attached. Position: Irregularities of individual teeth which the patient washes to have reproduced in his dentures will have been described at, or before, the try-in stage, and the complaint under consideration is that the teeth arc too far back in the mouth, or arc too far forward, more often the former. If the setting-up is left entirely to the technician without any instruc- tions he will, quite rightly, place them as nearly over the remaining ridge as he can, but if the patient has been edentutous for some time the labial absorption of the upper alveolus makes this the wrong position for the anterior teeth. A fear is some- COMPLAINTS 381 times expressed that moving the teeth anterior to the ridge, into the position the natural teeth occupied, will affect the stability of the denture, but this is not so. Stability will be jeopardized much more by encroaching on the tongue, than bv setting the teeth in the neutral zone where pressures of tongue and lip are equalized. A further point to be remembered is, that a patient who has been edentulous for a sufficient length of time for this degree of absorption to have taken place, will almost certainly have been wearing dentures, and will have acquired a considerable degree of muscular control. Treatment: New dentures will almost certainly have to be made. If only the anterior teeth of the existing denture are moved forward, larger ones will be required if proximal contact is to be maintained, and this is contra-indicated if the teeth original])' chosen were correct; if the teeth are to be moved back the converse is equally true. (e) Amount of Tooth Showing This complaint is nearly always with regard to the upper anteriors, and will be that either too much or too little tooth is showing. It must be remembered that the upper natural teeth show less in old age than in youth, owing to attrition and laxity of the lips. Treatment: Usually the dentures should be entirely re-made with the occlusal plane raised or lowered as the case may be, with longer or shorter anterior teeth if necessary. If the com- plaint is that too much tooth is showing, there is a temptation to grind away the offending portion, but this will ruin a balanced articulation since the patient will be unable to ■obtain incisive contact. (/) General Dissatisfaction One of the most difficult cases with which a prosthetist may have to deal is that of the patient, fitted with new dentures, who returns a few days later with the vague remark that he *docs not like them’. He can specify no particular complaint and it will be found on questioning that comfort, retention, stability and efficiency are not at fault, so the conclusion, which is invariably right, is that it is a question of appearance. 3 ^ 2 CLINICAL DENTAL PROSTHETICS It may be due to diffidence on the part of the patient who is unwilling to make a specific complaint which would appear to criticize the operator’s skill. If the prosthetist is fortunate enough to have a spare room, and the right type of sympa- thetic surgery assistant, he is well advised to lease it to her: rarely will she fail to find out what is really in the patient’s mind, although it may take a considerable time. Somcti mes the patient will bring a photograph to illustrate what he used to look like and what he was expecting the prosthetist to reproduce. These photographs are almost entirely useless, whether studio portraits or snapshots, as they were invariably taken many years previously, often thirty or more. If the complaint can he pinned down to one particular point it can, of course, be remedied, at least partially', but if it is a psychological longing for lost youth it will take much tact to satisfy the patient that the colour of the hair, the complexion and the tone of the muscles have all altered, and that the teeth alone cannot pro- duce the desired effect. These patients arc almost all women and the vast majority arc middle-aged spinsters often at the menopausal period; impatience or harshness will only antag- onize them but with tact, kindness and genuine sympathy they can almost always be brought to see the matter in its true proportions, and thereafter arc among the operator’s most enthusiastic practice builders. 3 . Inefficiency (a) Inability to Eat Anything This complaint is mainly confined to patients who arc wearing full upper and lower dentures for the first time, and arc impatient at the time which must be spent in acquiring new habits of eating. Careful attention by the operator to the psychological approach to denture wearing, as described in Chapter III, will eliminate this complaint except in rare cases, and these must be persuaded to persevere, so that t/rej will either learn anew how to eat, or will define some specific complaint which can then be remedied. (6) Inability to Eat Meat This is a complaint which may be made of new dentures. COMPLAINTS 383 never old ones, though the wearer” may have had previous full dentures for many years. It may [be due to: (i) Flattening of the Cusps of the posterior teeth by over- enthusiastic spot-grinding to correct an unbalanced denture. (ii) The Use of Cuspless Posterior Teeth. (iii) Oierclosure with its decreased muscular efficiency. (iv) The Use of Acrylic Posterior Teeth due to their resilience and softness. (v) Unbalanced Articulation which will not allow the teeth on the balancing side to remain in contact during the lateral movements necessary to shear through food fibres. (vi) Cuspal Interference preventing free lateral movements, under which heading is included, too great an oveijet for the degree of overbite, or an incorrect incisive angle. (vii) Inexperience on the part of a patient wearing his first full dentures, when none of the foregoing faults are present. Treatment: Haring discovered which of these faults is the cause of the complaint, the remedy is sufficiently obvious to require no further mention. (c) Dentures Dislodged by Eating This is applicable to either or both dentures and the common causes are: (i) Cuspal Interference , which has already been discussed as has also (ii) Unbalanced Articulation. (iii) Upper Teeth Outside the Ridge , which may cause the denture to tilt down on the non-working side. This is particularly liable to happen if the upper ridge is narrow bucco-palatally, if the maxillary tuberosities are very small, if the buccal sulcus is very shallow, or in cases with mandibular protrusion. Treatment: Re-make the dentures, if necessary, with a crossed occlusion. (iv) Insufficient Tongue Space will often cause the lower denture to be moved about during the process of eating, though it may be stable under other conditions. 3*4 CLINICAL DENTAL PROSTHETICS Treatment: Re-make, allowing more tongue space, using narrower posterior teeth if necessary. (v) Periphery Overextended. - It is quite possible Tor a denture to be slightly overextended and yet to be stable during speech and swallowing. This is because movements during eating are more extensive than those employed when trimming the periphery. The commonest place for them to occur is in the region of the posterior lingual pouch. It is frequently difficult in these cases to locate the exact area of overextension, since the tissue contact with it is too intermittent to cause pain or hyperaemia. Intelligent observation by the patient of the exact movement which causes the instability will eventually enable the operator to locate the overextension. Treatment: Cut away the excess. (vi) Inexperience. - The posterior natural teeth arc often lost some time before the anterior ones, with the result that a habit is formed of eating on the anterior teeth. When full dentures arc being worn for the first time, it is only natural that the wearer should try to continue his previous eating habits in these cases with bad results. Most experienced wearers of full dentures have such excellent, though uncon- scious, control of them that they can bite into an apple, or eat com ofT the cob, with little difficulty, but this automatic skill can only be acquired with time and patience. Biting, which is the function of the anterior teeth, as opposed to chewing, which is the function of the posterior ones, is the last thing which the new denture wearer should attempt. When he has mastered this he has learnt denture control. Treatment: Careful explanation to the patient, followed by perseverance on his part. (vii) Eating Causes Pain. - This has already been described under the heading of pain to which reference should be made. 4 . Poor Retention (a) When Opening the Mouth Patients more often complain that the lower denture lift* than that the upper one drops. If this lifting only occurs when COMPLAINTS 385 the mouth is widely opened, as in yawning, it should be explained that this is normal. The following are the usual causes: (i) Overextension This has already been discussed under the heading of pain, the difference in these cases being that the overextension is so slight that the tissues do not make constant contact with it, and consequently soreness does not arise. The treatment is identical. (ii) Tight Lips These can be a most potent source of trouble when in conjunction with a flat, ridgeless lower. The inward pressure from these tight lips will seat the upper denture more firmly in position but will push the lower denture backwards and upwards. Treatment: Re-make with the lower anterior teeth set more lingually, with a definite labial concavity on the denture, and with the maximum extension in the region of the retromolar pads. Alternatively gum-fit the lower anterior teeth. (iii) Tongue Cramped There are two causes for this complaint, one is that the lower posterior teeth are tilted lingually producing an under- cut area into which the wide middle-third of the tongue will press, when movements of the tongue will lift the denture. The second cause is setting the lower posterior teeth too far lingually, possibly to avoid a crossed occlusion, so that any movement of the cramped tongue will cause a tilting of the lower denture. Treatment: Re-make the dentures allowing more tongue space, if necessary by crossing the occlusion or by using teeth which are narrower buccolingually. (iv) Underextension This fault is by no means uncommon, and its effect on the retention of the denture is most marked. Maximum retention cannot be obtained without covering the greatest possible denture-bearing area. Some very careful operators produce this fault by placing excessive tension on the soft tissues during the peripheral moulding of the impression, through their 3^6 CLINICAL DENTAL PROSTHETICS desire to avoid overextension. Where this cause is suspected of being the fault, it can be checked by using tracing composition round the periphery, moulding it carefully and noting the result. Treatment: Moulded tracing composition replaced by denture-base material. (v) Lack of Peripheral Seal Retention will have been poor when the dentures were first inserted, and the operator may have persuaded the patient to wear them for a few days in the hope that they would “bed-in”. Treatment: Tracing composition round the periphery, fol- lowed by a wash impression with zinc oxide paste, and re-lining. (vi) Lack of saliia or a very thin watery saliva. There is no specific treatment for this condition but persever- ance will give a certain degree of muscular control. This cause only applies to the upper denture. (b) When Coughing or Sneezing Occasionally a new denture wearer will complain that his upper denture falls and his lower denture lifts, whenever he coughs or sneezes violently. Treatment: It must be explained to the patient that when coughing or sneezing there is a moment when the pressure of air in the mouth is greater than atmospheric pressure, so that the peripheral seal of the upper denture is broken and it is able to fall: also there is unusual muscular movement which will cause the lower denture to lift. There is no way of prevent- ing these mo\ cments of the dentures, but they are a very minor inconvenience. 5 . Instability This question has already been discussed in relation to its two main, causes*. (a) When Ealing: Under the heading of inefficiency. (b) When Talking: In Chapter X on phonetics. COMPLAINTS 387 (c) The Defensive Tongue: Some individuals have what may best be described as a defensive tongue. It is primarily concerned with preventing any foreign body other than food reaching the pharynx or remain- ing in the mouth. When dentures are fitted it subconsciously but positively ejects them and the patient finds it difficult or impossible to train a tongue of this type to control the dentures. Such a tongue is illustrated in fig. 280. Note how it is with- drawn into the mouth and is under the denture instead of on top of it. Treatment: Persuasion to develop correct tongue habits. If this does not succeed, springs. 6. Clattering Teeth The noise appears to be considerable to the patient and it is, in fact, frequently audible to his fellow diners. There are two main causes for this complaint of which the first mentioned is the most common. 3^6 CLINICAL DENTAL PROSTHETICS desire to avoid overextension. Where this cause is suspected of being the fault, it can be checked by using tracing composition round the periphery, moulding it carefully and noting the result. Treatment: Moulded tracing composition replaced by denture-base material. (v) Lack of Peripheral Seal Retention trill have been poor when the dentures were first inserted, and the operator may have persuaded the patient to wear them for a few days in the hope that the)* would “bed-in”. Treatment: Tracing composition round the periphery, fol- lowed by a wash impression with zinc oxide paste, and re-lining. (vi) Lack of saliva or a very thin watery saliva. There is no specific treatment for this condition but persever- ance will give a certain degree of muscular control. This cause only applies to the upper denture. (b) When Coughing or Sneezing Occasionally a new denture wearer will complain that his upper denture falls and his lower denture lifts, whenever he coughs or sneezes violently. Treatment: It must be explained to the patient that when coughing or sneezing there is a moment when the pressure of air in the mouth is greater than atmospheric pressure, so that the peripheral seal of the upper denture is broken and it is able to fall: also there is unusual muscular movement which will cause the lower denture to lift. There is no way or prevent- ing these movements of the dentures, but they' are a very minor inconvenience. 5 . Instability This question has already been discussed in relation to its two main causes: (а) When Eating: Under the heading of inefficiency. (б) When Talking: In Chapter X on phonetics. COMPLAINTS 387 (r) The Defensive Tongue: Some individuals have what may best be described as a defensive tongue. It is primarily concerned with preventing any foreign body other than food reaching the pharynx or remain- ing in the mouth. When dentures arc fitted it subconsciously but positively ejects them and the patient finds it difficult or impossible to train a tongue of this type to control the dentures. Such a tongue is illustrated in fig. 280. Note how it is with- drawn into the mouth and is under the denture instead of on top of it. Treatment: Persuasion to develop correct tongue habits. If this does not succeed, springs. 6. Clattering Teeth The noise appears to be considerable to the pauent and it is, in fact, frequently audible to his fellow diners. There are two main causes for tins complaint of which the first mentioned is the most common. 3 88 CLINICAL DENTAL PROSTHETICS (tf) Too Great a Vertical Height This will cause the teeth to come into contact sooner than expected and therefore noisily. Treatment: Reduce the height. (b) Gross Cuspal Interference Complaints from this cause arc rarely met without the accompanying complaint of instability, but in cither ease it is easily distinguished from too great a vertical height. Treatment: This is as already described under the heading of pain. 7 . Nausea Although this subject has been discussed from the point of view of impression taking, there arc some essential differences when considering nausea in relation to wearing a full upper denture. The cause of the sickness is the same in both caics, light or intermittent contact on the soft palate or back of the tongue, and the patient’s complaint is almost invariably ‘that the upper denture goes too far back and makes me feel sick’. The causes arc: (a) Denture Slightly Overextended Rare, but, if it does exist, the movements of the soft palate will cause it to make intermittent contact with the denture. Easily diagnosed by observing the relation of the posterior border to the vibrating line. Treatment: Remove the excess and re-post-dam if necessary. (b) Denture Underextended If the posterior palatal border of the upper denture docs not extend, at least very slightly, beyond the termination of the hard palate it can rarely compress the soft tissues sufficiently to maintain close contact with them under all normal condi- tions, and this will often cause nausea for the following reasons. (i) Intermittent Contact The denture moves owing to an inadequate air-seal. (ii) A Palpable Edge The edge is detected by the dorsum of the tongue, owing to its being insufficiently embedded in the mticom membrane. COMPLAINTS 389 Treatment: Extend the denture almost to the vibrating line and post-dam adequately. (c) Thick Posterior Border This is a very common cause of nausea resulting from the dorsum of the tongue being irritated by the thick edge. The palatal edge of the upper denture should be thin, and slightly embedded in the compressed mucous membrane, so that the tongue is unable to detect any definite junction of denture and mucosa. Treatment: Thin down the posterior border of the denture. 8. Discomfort Patients sometimes complain that new dentures are not comfortable but can give no specific cause for complaint. These cases arc difficult to diagnose since they are not accom- panied by pain, and retention appears to be satisfactory, but as the patient has nearly always previously worn dentures a careful comparison of the new with the old will generally give a clue to the cause. The causes may be: (a) Cramped Tongue Space This is the most common reason for this complaint, the teeth on the new upper denture having been set-up on the centre of alveolar ridges which have absorbed considerably since the older denture was made. Since the absorption is greatest on the buccal aspect of the upper ridge, the teeth are now mounted nearer to the mid-line, so decreasing the tongue space. (ft) Altered Vertical Height It is more probable that this is extremely slight and is an unintentional opening of 1 mm. or 2 mm., but it may be sufficient for a sensitive patient to notice a difference, par- ticularly if the original dentures were made with a very small free-way space. (c) Altered Occlusal Plane Again, as in the case of an altered vertical height, the height of the occlusal plane is unlikely to have been changed by more than I mm. but even this slight alteration will require some adjustment of automatic muscular movement. COMPLAINTS 39I resultant bunching of the cheeks allows of their being caught between the occlusal surfaces of the teeth as they occlude. Treatment: Restore the vertical dimension or, if this is impossible, grind off the buccal cusps of the lower teeth. Biting the Tongue This is almost invariably due to a decrease in the tongue space occurring when fitting new dentures for patients already wearing dentures. 11. Food Under the Denture This complaint is usually made by patients wearing dentures for the first time and who have not yet learnt how best to control the food. Undoubtedly a perfect peripheral seal will prevent the ingress of food beneath the denture but perfection is rarely attained and, owing to alveolar absorption, never maintained. Scraping a groove in the model, along and near the entire periphery of the denture, is sometimes carried out but this food-line, as it is termed, usually causes some inflamma- tion and ulceration until it is finally established as a groove in the mucous membrane; it is rarely completely successful. Treatment: This usually consists of covering the maximum possible area and obtaining an adequate peripheral seal; thereafter, only perseverance by the patient can bring about any improvement. At the conclusion of this chapter it may be worth stressing that in the experience of the authors the six commonest causes of dentures failing are: (1) Incorrect antero-posterior relationship of the mandible to the maxilla. (2) Uneven and locked occlusion - this is always present unless a careful check record has been carried out. (3) Open vertical dimension - not necessarily gross but suffi- cient to deprive the patient of a freeway space. (4) A cramped tongue. (5) Poor retention - due to incorrect outline - usually under- extension of the periphery. (6) Failure to copy existing dentures when making new ones for an experienced denture wearer. 39 ° CLINICAL DENTAL PROSTHETICS Treatment: Unless any of the above-mentioned factors are gross the patient should be encouraged to persevere for several weeks, by which time, in most cases, the discomfort will have disappeared; but if it has not, then nothing remains but to make new dentures, accurately copying the old ones. 9. Altered Speech Reference should be made to the chapter on phonetics. When full dentures are first worn there is always some temporary alteration in speech owing to the thickness of the denture covering the palate, necessitating slightly altered positions of the tongue. Commonly this is only a temporary incon\ enience, most rapidly overcome by reading aloud; when there is an altered position of the upper incisors, a change in their palatal shape, or any reduction of tongue space, adaptation may be very difficult even with perseverance. Treatment : The dentures must be re-made paying particular attention to the principles laid down in Chapter X. 10. Biting the Cheek and Tongue Cheek Biting Two common causes for this condition exist: (i) Insufficient Overjet The normal occlusal relationship of the posterior teeth is with the buccal cusps of the upper teeth outside those of the lower teeth ; this arrangement normally prevents the cheeks getting caught between the teeth and bitten. If for any reason this arrangement has been altered, or if a patient lias very lax cheeks, cheek biting may occur. Treatment: Increase the buccal overjet and plump the denture; in some cases it may be necessary to remove the last molar teeth or grind the buccal surfaces of the lower posterior teeth so that the lingual cusps only will make contact with the upper teeth. (ii) Reduced Vertical Height If the vertical occlusal dimension is grossly reduced, the COMPLAINTS 391 resultant bunching of the cheeks allows of their being caught between the occlusal surfaces of the teeth as they occlude. Treatment: Restore the vertical dimension or, if this is impossible, grind off the buccal cusps of the lower teeth. Biting the Tongue This is almost invariably due to a decrease in the tongue space occurring when fitting new dentures for patients already wearing dentures. ii. Food Under the Denture This complaint is usually made by patients wearing dentures for the first time and who have not yet learnt how best to control the food. Undoubtedly a perfect peripheral seal will prevent the ingress of food beneath the denture but perfection is rarely attained and, owing to alveolar absorption, never maintained. Scraping a groove in the model, along and near the entire periphery of the denture, is sometimes carried out but this food-line, as it is termed, usually causes some inflamma- tion and ulceration until it is finally established as a groove in the mucous membrane; it is rarely completely successful. Treatment: This usually consists of covering the maximum possible area and obtaining an adequate peripheral seal; thereafter, only perseverance by the patient can bring about any improvement. At the conclusion of this chapter it may be worth stressing that in the experience of the authors the six commonest causes of dentures failing are: (1) Incorrect antero-posterior relationship of the mandible to the maxilla. (2) Uneven and locked occlusion - this is always present unless a careful check record has been carried out. (3) Open vertical dimension - not necessarily gross but suffi- cient to deprive the patient of a freeway space. (4) A cramped tongue. (5) Poor retention - due to incorrect outline - usually under- extension of the periphery. (6) Failure to copy existing dentures when making new ones for an experienced denture wearer. Chapter XV RE-LINING, RESILIENT LININGS, AIDS TO RETENTION AND REPAIRS The term re-lining is used to denote the production of a new fitting surface in an existing denture. Reason's for Re-uN'inc Owing to the fact that alveolar absorption is a continuous process, though varying in degree, the comfort, efficiency, stability, retention and appearance of dentures are ail liable to become impaired with the passage of time. Thus the reasons for re-lining a denture are: x. To Improve Retention and Stability Loss of fit will make the maintenance of peripheral seal impossible and will greatly impair the retentive effects of adhesion and cohesion. It may also permit a rocking or tilting of the denture during function and, in extreme cases in the lower, a lateral movement. 2. To Improve the Appearance One effect of alveolar absorption in the mandible is that the lower denture sinks below the original occlusal plane, and thus the patient has to close beyond the original vertical dimension in order to occlude the teeth. This over-closure is frequently noticed by the patient as a protrusion of the mandible and an undue approximation of the nose and chin, giving an appearance of age. Absorption of the upper alveolar ridge will not have so marked an effect on the vertical dimension because the hard palate does not materially alter. The original vertical dimension can often be restored by re-lining the lower denture alone. RE-LINING A DENTURE 393 3- To Restore the Vertical Dimension If the vertical dimension to which a denture was made is reduced, masticator)* efficiency is impaired, but the previous efficiency can usually be restored by rc-Iining. 4. To Restore the Evenness of Occlusal Pressure With any alteration in the fit of the dentures there will be some alteration of the pressure transmitted to the tissues when the teeth are brought into occlusion. This can be corrected, if of small degree, by careful grinding of the teeth, but if the balance is grossly disturbed re-lining the dentures is the simplest means of restoring the original conditions. 5. To Alleviate Pain If a denture has been worn with comfort and then becomes painful, it is usually due to the fact that the supporting tissues have altered allowing the dentures to tilt, rock or move, and thus transmit undue pressure to one area. Re-lining will alleviate pain arising from this cause. Impression Materials for Re-lining Those in general use for the purposes of re-lining arc: (1) Zinc oxidc-cugenol paste. (2) Composition or black gutta percha. (3) Plaster of Paris containing starch. (4) Cold cure acrylic. Ordinary plaster of Paris or sodium alginate may be used as re-lining impression materials, but they have the disadvantage of breaking and flaking away from the fitting surface of the denture as it is being removed from the mouth. Technique of Re-lining The periphery of the existing denture should be carefully examined for its relationship to the functional position of the sulci. If the denture border was positioned accurately when the denture was originally constructed, it will probably now appear slightly overextended, due to alveolar absorption. This excess denture flange must be trimmed away until the periphery is a fraction short of the functional level of the sulci. 394 CLINICAL DENTAL PROSTHETICS In addition, flanges which fit into undercut areas must be relieved so that the impression, within the denture, can be readily removed from the plaster cast, without fear of fracturing the ridge. A further point to consider is whether or not any substantial increase of the vertical dimension is desired, as this influences the quantity of material used lor the impression, and the manner in which the latter is obtained. When improved retention is the only consideration, a very thin layer of zinc oxide-cugenol paste is spread evenly over the entire fitting surface of the denture, which is then seated in position in the mouth and the teeth brought together in centric occlusion; a slight pressure is maintained until the material hardens. About 30 seconds after the insertion of the impression, the periphery is trimmed by suitable lip and cheek movements to record their functional positions. Lingual excess should be trimmed by the usual tongue movements, before the teeth arc brought into occlusion. In cases where the vertical dimension has to be re-established in addition to the fit, the layer of impression material used must be of greater thickness, and since zinc oxide-cugenol paste flows somewhat readily it will be found unsuitable (as the sole impression material) for use in cases which require a restoration of 3 to 4 mm. In such cases the lower denture should first be lined with composition and an impression taken with the teeth in occlusion. The thickness of composition used should be such that it almost restores the desired vertical dimension. The composition is then chilled, dried, and the final impression to the correct height taken with a film of zinc oxide paste. If the vertical dimension is being increased bejond 3 to 4 mm., and both dentures are being re-lined, the question arises which denture should accommodate the greater part of this opening. The lower ridge, in the majority of cases, will have absorbed more than the upper, and the hart! palate not at all. As a general guide, the incisal level of the upper anterior teeth should be studied in relation to the lip line, and the upper impression should be taken first, with sufficient thickness of material to bring the upper incisors into the desired position. RE-LINING A DENTURE 395 Although there is no apparent absorption of the hard palate, it will frequently be found that incisors, which originally showed to the extent of i to 2 mm. below the lip, have completely disappeared when the lip is at rest. This effect is caused by: (1) Upper alveolar absorption allowing the denture to tilt and rise anteriorly. (2) Some loss of muscular tone of the upper lip which thus tends to droop slightly lower than previously. The operation is completed by lining the lower denture with impression material of sufficient thickness to complete the increase in vertical dimension. Alternatively the complete impression may be carried out with composition alone. Whenever composition is being used, it is an advantage to grind away about 2 mm. from the fitting surface of the lower denture, except in cases of flat lower ridges, in order to allow for a greater thickness of material. It will be found that if there is only a wafer of composition it is very difficult to keep it in a soft, workable condition when inserting it into the mouth as it cools too rapidly; the greater thickness overcomes this difficulty. Black gutta percha, unlike composition, possesses the ability to flosv for a long time after it has been softened, and can therefore produce a thin accurate refine. A strip is cut from the sheet of gutta pcrcha, placed in boiling water for a few minutes, dried and laid on the dr)' fitting surface of the denture and then inserted in the mouth. As the patient occludes, the gutta pcrcha flows until the denture is fully and accurately seated. Peripheral movements arc also accurately reproduced by gutta pcrcha and the patient may even wear it for some days to allow complete functional adaptation before the gutta percha is replaced with acrylic. Should the upper denture need a thick layer of impression material to adjust the occlusal plane in relation to the lip line, or to eliminate excessive rock across the torus, the seating of the denture can be more accurately effected if some impression of the anterior and posterior ridges are obtained first in composition or softened wax. The stops so formed will 396 CLINICAL DENTAL PROSTHETICS Flo. 281 -Soft lining. Note thickness of lining. Thin linings are useless to relieve pressure pain. prevent loss of vertical height when the teeth arc brought into centric occlusion during the zinc oxide-eugenol impression stage. Improved retention and stability are obtained, when rc- lining a denture, if the periphery is carefully adapted to the functional level of the sulci with tracing compound. The areas of soft tissue, including the retromolar pads, which have been selected for post-damming, should be adequately compressed with the same material. Cold cure acrylic resin has been suggested as a material for re-lining dentures since it avoids any laboratory' technique and the inconvenience caused to the patient by being tempor- arily deprived of his dentures. The procedure involves lining the dried denture with a thin layer of this acrylic dough and placing it in position in the mouth, the mucous membrane haring previously been smeared with vaseline. The dough is allowed to polymerize in the mouth for a period of four RE-LINING A DENTURE 397 minutes, but no longer. The denture is then removed and polymerization completed in a warm water bath of approxi- mately 40° C., the time required being about ten minutes. The denture borders must be trimmed and polished. A serious disadvantage to the use of this material is the fact that acrylic dough often causes considerable and painful irritation of the mucous membrane. Resilient Linings fig. 281) When other causes have been eliminated and pain under the lower denture is considered to be due to the type of ridge formation and the susceptibility of the mucosa to bruising, which cannot withstand the transmitted pressure of mastica- tion, some relief of the symptoms may be obtained by re-lining the denture with a resilient material. The clinical procedure calls for a thin zinc oxide-eugenol paste wash in the existing denture; the remainder of the technique being carried out in the laboratory. This may involve reconstructing the denture in vulcanite incorporating velum rubber as a lining. Alternatively, sufficient material may be removed from the fitting surface of the denture, to allow for a thickness of 2 to 3 mm. of gutta- percha to be substituted and impressed on the ridge under occlusal stress; subsequently the periphery is moulded to the functional position of the sulci. This lining is of a temporary nature as it has to be replaced about every six months owing to its distortion in use. This technique is used only in cases where all other methods have failed. Polyvinyl chloride is a soft plastic which has been used as a resilient lining but which has been found to be unsatisfactory as the plasticizer leaches out and the material then becomes hard. At the present time a large number of proprietary resilient linings are available, many of them based on the synthetic rubbers. Some of these materials are very satisfactory and produce a comfortable denture. The life of the most resilient linings is limited to a year or two at the most and then they require renewal, but ir the patient is comfortable then frequent renewal is well worth while. 39^ CLINICAL DENTAL PROSTHETICS If the resilient lining is thick and is attached to an acrylic denture, the latter will soon fracture as a result of flexion unless a thick cast metal strengthener is incorporated on the lingual side of the denture. In the laboratory’ the re-lining of a denture may be carried out by merely replacing the impression material with the denture base material, after suitable means of retention have been prepared for it. Alternatively part, or the whole, of the denture base may be replaced, using the existing teeth, or new teeth. The use of such confusing terms as rc-base, re-model and re-make have been avoided as they arc merely variations of re-lining methods. Techniques in which trays arc used for impression taking, followed by the usual stages of denture construction, except that the teeth of existing dentures are remo\ed and used again, are virtually new dentures and should be considered in that category’. The terms rc-base and re-make are apt to confuse the layman and to suggest the idea of something inferior. Repairs Unfortunately there is a tendency to regard denture repairs as a constant evil, without any necessity to find out the cause of the breakage, with the result that many dentures are mended only to break again shortly afterwards, when they should be either re-lined or new' dentures constructed. It cannot be too strongly emphasized that no denture which breaks in the mouth should be repaired without the cause of the breakage being ascertained. Before considering the principal causes of breakage it should be pointed out that quite a number of dentures which are brought by patients as having cracked in the mouth, ha\c in fact been dropped. The crack which was started by the accident has passed unobserved, and the stresses of mastication have completed the fracture. These cases are often impossible to diagnose as patients will rarely, either through forgetfulness or untruthfulness, admit that they have ever dropped the denture. . . Fractured dentures, whenever possible, should be united with sticky wax and strengthened with wire, and tried in the RE-LINING A DENTURE 399 mouth for perfection of fit before being repaired. Where the fit is found to be deficient it will be necessary to re-line the denture after it has been repaired, or otherwise a further fracture will occur in a very short time. Warpage resulting from one repair frequently causes a second fracture. Dentures made of methyl methacrylate will warp to a certain extent each time they are re-cured and very rarely is the fit of an acrylic denture satisfactory’ if it has been repaired more than twice, the resultant bad fit being a common cause of further breakage. Breakage of a denture in the mouth almost invariably starts with a small crack, spreading across the denture rather as though it were being tom instead of broken. Often the first thing to be noticed by the patient is the sensation of the feel of a hair on the denture - a hair which cannot be moved - and a very close inspection is often required to see the small crack at this stage. Breakages arc of two main kinds: (1) Fracture of the denture base. (2) Fracture of a tooth or teeth on the denture. Fracture of the Denture Base 1. Poor Fit Causes. This is a very wide term and can more readily be described under separate headings: (a) Alveolar Absorption This will be found to be the cause of breakage in dentures which have been worn for some considerable time, or which were made shortly after the extraction of the teeth. The alveolar absorption will cause the denture to be unevenly supported and is a common cause of fracture. (b) Warpage Warpage, as a cause of fracture, is almost entirely confined to the acrylic resins and is also a very common cause of further fractures of a denture which has already been repaired. Vulcanite may also warp if incorrectly treated - for example, cooled too rapidly on removal from the vulcanizcr or 400 CLINICAL DENTAL PROSTHETICS revulcanized many times. Metal dentures also are capable of distortion with faulty handling either in soldering, heat treating, or welding. (c) Inadequate Relief Unless a self-relieving impression technique has been employed, such as a compression impression, or adequate empirical relief has been provided, in mouths exhibiting gross variations in the thickness of the mucous membrane, the denture will flex over the hard areas of the palate and fracture. { the most exposed tooth, the lateral inenors just show and the canine is seldom seen. exposed during conversation and usually the focus of attention when an individual smiles or laughs (fig. 290), and therefore the selection of the right mould of central incisor is important. There arc two main points to be considered in its selection, firstly the sex, and secondly, the personality of the patient. One associates the female form with curves whilst the male form presents angles and straight lines (figs. 291, 292). If this is trans- lated into tooth mould then a central incisor selected for a female should have a basically curved outline with rounded mesial and distal corners; such an outline is often referred to as the ovoid mould. The basic mould for an incisor for the male should be a straighter sided tooth with moderately sharp mesial and distal corners; the tapering or square mould (fig. 293). This does not mean that all women must have ovoid teeth and all men square or tapering teeth. Obviously the Venus de Milo type represents the group of individuals who would probably be most suited to a truly ovoid tooth, but the athletic, manly and more angular female, although basically requiring teeth with curved outlines would not want these accentuated, and square and tapering type teeth with 420 CLINICAL DENTAL PROSTHETICS FlC 291. -The outline of the female figure tendv to be a senes of curves and the basic tooth form should be of the curved sided or ovoid type. Fig 292 - The outline of the male figure is more straight lined and angular in contrast to the female form and the basic tooth form should be tapering or square. rounded mesial and distal comers could be most effective. The male on the other hand, may not always produce the angular and straight outline and a slighily curved tooth may be acceptable provided the mesial and distal corners arc not over round. Thus, basically, we have curved outlines and curved comers for the female, and straight lines and sharp comers for the male ( see figs. 291, 292). APPEARANCE 4*1 Fio. 293 - Leri: Cimed tooih form suitable to ihe female S alient. Centre and right: Tapcnng and square tooth forms a\ing sharp angled mesial and distal comers, suitable to the male patient. The second point, that of personality, should be considered carefully when making the choice of tooth mould. Personality for this purpose is considered from the aspect of the physical and temperamental impression created by the patient. It cannot have a very precise bearing on the tooth selection, but nevertheless may prevent the choice of a wrong mould. There are two extremes of individuals to be considered, those who fall into the category of healthy, manly, muscular and active types, classed as a vigorous group and those who fall into the category’ of frail, timid, inactive individuals, classed as a delicate group. Ranging between these two groups will be those persons belonging to the average group. The greater proportion of individuals in the delicate group will be female whilst those in the vigorous group will be male. There will, however, be females ranging from the average group towards the vigorous group, such as some business executives and the committcc- lady-chairman types, and to a lesser degree males ranging from the average group to the delicate group, for example, the effeminate or small-boned or debilitated types. Obviously the 422 CLINICAL DENTAL PROSTHETICS average group will be by far the largest and the vigorous group will be greater than the delicate group. Mould selection based on this grouping means that on the one extreme the tooth should be soft in its outline with cuncs and no sharp angles and a smooth labial surface - the delicate group, and on the other extreme the tooth should be bold, angular and show pronounced surface detail labially (ridges and grooves) - the vigorous group. If the personality is considered in conjunction with sex then the vigorous male would be suited best by a bold tapering tooth with sharp angular corners and a prominently contoured labia! surface, whilst a delicate female might best be suited by a thin ovoid, smooth surface tooth (fig. 294). Square Fig. 294. -Right: Bold tapering tooth suitable to the vigorous male. Left: Smatl, delicate curved tooth suitable to the delicate female. Centre: An average size and mould of tooth suitable to the average group of individuals. teeth are considered to be less vigorous than tapering ones but more vigorous than the ovoid type. The lateral incisors aid considerably in creating the effect of vigour or delicacy and range from a long, tapering, square cornered tooth to a small narrow, round cornered tooth respectively, the lateral of average length and width and with a rounded distal corner suiting the average group of individuals (fig. 295)- APPEARANCE 4*3 FlO 295. -Left: A \ itjorcKH lateral inenor. Centre • An average lateral incisor. Right A delicate lateral tnctvir 2. Tooth Size This will be governed partly by the sex and personality and partly by the physical build and lip mobility of the patient. With the natural dentition there arc instances of slightly built individuals having large teeth and heavily built people having small teeth. This is often a conspicuous feature of the person and attracts attention. For this reason, since it is desirable that dentures should be an unobtrusive feature of the patient, it is advisable to select a size of tooth which blends with the general height and build of the patient, disregarding obvious obesity, and not necessarily related to the size of the patient’s head. However, the length to breadth ratio of the selected tooth should bear a very close relationship to the length to brcadtli ratio or the person’s head (fig. 29G a, b, c). One important factor which must be borne in mind when deciding the size of tooth, and also the level of the incisal edge relation to the lip, is the mobility of the upper lip. Obviously it is desirable to expose as little denture base material as possible when smiling and laughing and therefore a balance often has to be struck between tooth length and incisal edge level in order that the general tooth size may be kept in proportion with the patient’s CLINICAL DENTAL PROSTHETICS Fig. 396(0) build. A slightly built patient with a very' mobile lip may June to ha\e the incisal edge, which would normally have been set 2 to 3 mm. below the lip, raised to lip level or slightly higher in order that a tooth of balanced length may be used instead of an overlong tooth. Provided the tooth maintains proportions suitable to the individual the appearance will be best if the tooth fills, or very nearly fills, the space between the rest and smiling positions of the upper lip. The size of the wvowth will control the vdtUh of the tooth to a certain extent. It is obviously undesirable to select narrow teeth for a person with a very broad smile which exposes the molar teeth, but it is equally undesirable to select very broad teeth - which will also be proportionate in length - if the sex, personality and physical build of the individual indicates a w Fig. a$6 - Comparison of tooth proportions lo face propor- tions Facial measurements are taken across the zygomatic process on each side, and from the supra -orbital ndge line to the inferior border of the chin ( »i/r. Lower right. I arge sired teeth - large male form. the size of the natural teeth docs not change throughout life, excluding the effect of attrition hut the body often undergoes considerable alteration in weight and therefore (he dimensional changes sometimes occurring in middle age may he misleading when considering the size of teeth. It is a common failing to select artificial teeth which arc too small and this frequently results from the patient influencing the operator in his choice. Patients often imagine their natural teeth to have been smaller than was actually the ease hut it must be pointed out that there is an element of risk in pressing one’s own choice of size and mould too vigorously. A com- promise is sometimes necessary between that which the operator considers suitable and that which the patient desires, which with some elderly ladies may be small, white teeth. APPEAR Ay CE 42 7 3 . Shade of Teeth There is no rule which can be applied to the selection of the correct shade of tooth for an individual. Generally it is a question of trial and error, taking a tooth of one colour from a shade range, placing it in position behind the upper lip and assessing its colour tones in relation to the facial colour tones of the patient. This operation is repeated with different shades until one is found which most satisfactorily blends with the patient’s general colouring. Blondes with light blue or grey eyes arc usually best suited by a light ivory-yellow shade of tooth bordering on the white range. Darker eye colouring mav require a slightly darker shade of tooth. Brown hair and medium coloured eyes call for the mid range of the biscuit yellow shade, and the darker hair and eye tones will require a darker shade of the biscuit yellow range. Occasionally a gre\ basic tone blends well with the elderly or pale debilitated individual, but its selection requires careful consideration, or the effect when the patient smiles is to accentuate the debility . Age has an important bearing on colour choice. Natural teeth tend to darken with age and the colour selected for a person of 25 years of age would be too light when that person was 50. Tor instance in the Peridon shade range 65 is found to blend well with the larger proportion of young adults whereas the shade 79 suits a larger proportion of those of 50 years and over. Both these shades are basically a biscuit yellow. The best advice for the student is to note the shades of teeth used in partial denture work and to categorize them according to the age and colour tone of the individual and relate this informa- tion to full denture construction. Selection of colour should always be made from a wet tooth under the shadow of the upper lip, the position which it will occupy and never from a dry' tooth held in the hand. The Pwili&n tf die T«lh Since our chief aim is to produce a denture which harmonizes with the person’s appearance, presents a pleasant effect when smiling or laughing and is not conspicuously artificial, the question of tooth position is also important. Basically there are two considerations. Firstly, the person, male or female, who has 428 CLINICAL DENTAL PROSTHETICS classical features requires a normal arrangement of tooth posi- tion, otherwise their classical qualities will be diminished (fig. 298 a, b, 299). These will be very few indeed. Secondly, the very nigged type of individual requires irregularity in the positioning of the teeth as othenvise a perfectly normal arrange- ment of the teeth would contrast with the rugged features and therefore bring the focus of attention on to the denture, which is not desirable (figs. 300, 301 a, b). Most patients will be placed somewhere between these two extremes and many variations from the normal position of the individual anterior teeth will be found. Once again it is helpful to consider tooth position in relation to the personality and sex of the patient. There is, however, a third factor — that of age which also influences the arrangement of the anterior teeth. This latter point will be discussed under heading 5. APPEARANCE (4) Fie. 29C. - Well proportioned and attractive facial features requiring a fairly regular setting of the anterior teeth. (fl) Osoid facial type. (4) Regular appearance of the natural teeth. Apart from their ability to incise food and aid speech the anterior teeth form the main feature of the smile and largely influence facial expression. In order that they should fulfil these latter two functions satisfactorily it is important that the teeth should be placed in relation to the alveolar ridge in such a manner that adequate support is given to the lip during a smile (fig, 302), and that the lip is supported in its natural forward position when the lip is at rest. Too often artificial upper anterior teeth arc set back underneath the ridge (fig. 303 c, b t c, d) and the lip hangs down vertically or may even fall inwards. If fig. 304 is studied, which is a sagittal section of a maxilla and full upper immediate denture three months after 430 CLINICAL DENTAL PROSTHETICS Fig agg. - Note curve-sided central incisors, rounded mesial angles of lateral indsors, attrition of incisal edges of the centrals and canines, and the stippling of the gingival tissues. Fig. 300 — An arrangement of the teeth suited to the robust male !)-pe. N ole, p alataiiy rotated laterals, attrition of the incisal edges and increased details of the labial surfaces of the teeth. Tig. 301 (a and b). - Vigorous setting or the anterior teeth tued to emphasise male chantc tern lies. APPEARANCE ' 433 Fic. 303 1*) (a) Appearance with prev ious denture. (i) Appearance with new dentures. (e) Mould and arrangement of teeth of the previous denture. (d) Mould and arrangement of teeth of the new denture. Note: The more oval type of tooth selected for the new denture in which the /i has been rotated and set forward in the arch and slightly ovetlapping the i/. The /a is rotated and slightly spaced in relation to It. The denture base has been contoured and stippled Frc. 304. - Sagittal section through a model of the maxilla and an immediate denture dirte months after its insertion. Note the upward and backward resorption of the alveolar ridge, the upper incisor was ‘socketed* initially. APPEARANCE 435 insertion, it will be seen that alveolar absorption of the anterior ridge has been upwards and backwards and that the necks of the anterior teeth are positioned forward of the ridge and the relationship of the whole tooth is somewhat forward of the ridge. These teeth would be supplying the correct lip support since they arc an identical replacement of the patient’s natural teeth. This indicates the necessity for setting anterior teeth in a forward relationship to the ridge in almost all cases. The degree of this forward placement is related, ob\ iouslv, to the extent of absorption which has occurred anteriorly and to factors of mechanics and retention associated generally with the con* struction of the dentures. The aim should be to restore correct lip support and with this point established, the individual positions of the teeth can be considered with a view* to pro- ducing a harmonious appearance. The Central Incisor. - Keeping both incisors in identically correct positions indicates perfection and would probably onlv suit those with classical features. If one incisor is moved forward of the other at its incisal edge then a somew'hat harsh appear- ance is created which would be suitable to a few male persons. On the other hand if we start from the correct positions of the centrals and move one out cervically leaving the incisal edges in line a softer irregularity is created suitable for use with the female patient. A more vigorous effect can be obtained by bringing one central bodily forward of the other - the vigorous male type. Further effects of softness or hardness may be brought about by rotating or inclining laterally one or both incisors (fig. 305 a, b ). Overlapping can be effective particularly in the female where the canine to canine distance requires to be small but the tooth size average. In most instances the varia- tions of position of the central incisors are acceptable to both sexes. It is usually a matter of degree of irregularity which needs consideration in relation to the sex and personality of the patient. The Lateral Incisor. — Although this is a comparatively small tooth and less apparent than the central it does however play an important part in establishing the sex and personality factors associated with the general composition of the anterior 436 CLINICAL DENTAL PROSTHETICS (« Fig. 305 (a) and (4). - Illustrate the rotation or central incisors to break up an otherwise regular setting of the anterior teeth. Acceptable to both male and female depending on 1 he degree of rotation. iceth. If the lateral incisor is rotated so that the mesial surface is brought forward then the effect of the smile is one of softness; the tooth may overlap the central. By depressing the mesial edge towards the palate the effect of hardness is obtained. Lateral inclination from the normal vertical axis is an addi- tional variation (figs. 306 a, b, 307 a, b). APPEARANCE 437 «) Fiq. 306 (a) and { b ). - Illustrate the use oflabial rotation of the incisal lips of the lateral incisors to accentuate cun-ature of the antenor arch when producing a feminine effect. The Canine. - This tooth should be set with the neck more prominent than the incisal tip and its long axis vertical. The more prominent the position of the canine and its cervical edge in the arch the more vigorous the smile becomes. Similarly the larger the tooth and the more marked the labial surface detail the greater the effect of masculinity. (>) Fig 307 fa) and (6). - Illustrates the use of palatal rotation of the mesial tips of the lateral incisors to harden the appear- ance by producing a more straight-lme effect of the anterior arch; used when producing a masculine effect. Feminity can be accentuated by setting the anterior teeth with a curvature running from the tips of the central incisors upwards to the canines (fig. 308). This imparts a sense of roundness to the smile. Symmetry should be avoided when producing irregularities APPEARANCE 439 Fig. 308. - Femininity accentuated by the upward curvature of the setting of the incisal edges, the centra] incisal Jine sweeps up to the laterals and continues upwards to the canine tips. Note the contouring of the labial flange and Us stippling. as they frequently increase the appearance of artificiality. On the other hand over accentuation of an irregularity is often necessary to be effective and a tooth arrangement which appears somewhat grotesque when set in the articulator becomes pleasantly acceptable when the denture is fitted in the mouth. 5- ->>S‘ Age in relation to appearance must be considered from two aspects. One, chronological age and two, the physiological age of the patient. People vary considerably in the effect of age on their physical appearance, some young middle-aged people appear very much older than their chronological age, whilst some chronologically old people appear young and virile. Tooth selection and arrangement should fit in chiefly with the physiological age of the patient. A person at the age of 18 years would probably have teeth of a uniform colour and would still retain the bluish tint of the 44 ° CLINICAL DENTAL PROSTHETICS incisal enamel but twenty-five years later these same teeth are likely to have undergone certain changes. They will have darkened slightly, areas of stain will have appeared, caries attack and subsequent fillings will have caused localized colour change, gingival recession wall have exposed cementum and attrition of the incisal edges will have removed the greater proportion, if not all, of the incisal enamel. It is to be expected that the surface colour change will be greatest in smokers though food stains such as tannin and cafiein for example will also have a marked effect. All this is progressive -with age and should be borne in mind when deciding on the colour of the teeth selected for an individual. In certain circumstances effective results can be obtained by varying the shade of one or two of the anterior teeth and also by staining and simulating fillings in individual teeth, alternatively the dental manufactur- ing companies produce such teeth, which are referred to as naturalized or characterized teeth. Even if such desirable pro- cedures are not adopted the standard set of anterior teeth can be made more balanced to the person’s age by judicious grinding of the incisal edges, and a study of the attrition of natural incisors will indicate the type of wear which occurs from person to person. Fig. 309 shows the expected appearance of a canine tooth at three stages of life. Attrition w ill obviously affect the posterior teeth as well as the anterior teeth so that if a patient of middle or advance age is likely to show the prcmolar teeth when smiling or laughing a more natural effect can be created if the cusps of the premolars are suitably ground and not left in the form of a newly erupted tooth. APPEARANCE 441 Age also has a bearing on the position of the anterior teeth. Throughout life natural teeth are usually being lost for one reason or another and this means that the contact points of the remaining teeth become less firm or even lost, particularly if a partial denture is not fitted (fig. 310). It is not an un- common state in the middle-aged person, where some posterior teeth have been lost, to find that the contact points of the Tig. 310 - Spacing of natural teeth due to loss of posterior teeth (patient age 29). anterior teeth have parted to the extent that the point of a probe can be passed freely between them, and this fact needs to be considered in relation to the setting up of the anterior teeth. Frequently the appearance of a full upper denture constructed for the 50-60-year-old patient is spoiled by having the teeth set with very tight contact between each tooth, producing an effect which is generally associated with youth. Varying degrees of spacing with either all or one or two of the anterior teeth aids in establishing a natural appearance in relation to age (fig. 31 1 a,b,c). A slight diastema between the centrals is a common occurrence but caution is necessary in reproducing APPEARANCE 443 this state as it is possible that if exaggerated it may appear unpleasant and become a source of amusement to the observer: it may also be an embarrassing food-trap. The gingival con- touring of a denture should also be related to the age of the patient and is the next consideration. Just as tightly contacting teeth are predominantly associated with youth so are normal, triangular, sharp-pointed interdental papillae indicative of the young person (fig. 312). Greater Fir. 3:2. — Natural gingival margins of youthful appearance: narrow, sharp pointed interdental papillae, suppled gingival tissue. harmony in the appearance can be obtained by simulation of some of the changes which may occur throughout life in the shape and colour of the interdental papillae and gingival mar- gins. Variation from the normal type papilla suitable to the youngish patient must be made with care, and spaces such as occur between teeth in ad\anccd periodontal lesions should be avoided. However, the copying of some of the less advanced conditions in which the point of the papilla is rounded instead 444 CLINICAL DENTAL PROSTHETICS of pointed and the base is widened to overlap the labial and cervical areas of the tooth to a greater extent than normal can be most effective, especially if the gingival margin is thickened to form a slight rolled effect (figs. 313, 314, 3 r 5 , 316). Denture base materials having reddish fibres or granules incorporated in them improve the general effect in some instances. A study of natural conditions which are not unpleasant in their appear- ance will be of considerable help to the student. Fig. 317 shows age changes which may be associated with the interdental papilla. In the production of such interdental papillae, certain points need remembering. (1) There should be a variation in the individual length and the degree of simulated change in the health of the tissue from papilla to papilla. (2) They must be related to the age of the patient. (3) They must be convex in all directions to avoid food being trapped about them. (4) They should extend to the contact points of the teeth and fill the interdental space so that no areas exist for food accumulation. This necessitates care in the selection of the tooth mould in order to avoid those moulds haring low contact point areas which would mean overlong papillae. 6. The Gingical Margin and Labial Surface Contour As previously stated, the gingival margins can be blended to suit the age by thickening or rolling the gingival margin of all or some teeth. In youth the margin is thin and pale pink in colour, in middle age an average appearance would be a slight rolling of the margin with increased red tint in the pink colour and the papillae would be blunter and thicker, whilst in advanced age the gingival tissue would give a characteristic thickened appearance and a deeper red tint, the papillae being broad based with very rounded apices (see figs. 313-316). The gingival level of the individual anterior teeth should vary, the central incisal gingivae normally being higher than those of the lateral incisors, but lower than those of the canine (fig. 318). Again symmetry needs to be avoided and variation in the APPEARANCE 445 Fig. 313.- Youthful appearance of the interdental papillae showing slight thickening of the gingival margins Note the use of overlap with the central incisors and the broadening of the base of their interdental papillae Fig. 314. — Illustrates a short, rounded and blunt papilla between It 2 which are also spaced. Tic. 315. -A \«t> broad bavd papilla between 1/1 hat in? the effect of tapering an otherwiv tquare mould of tooth. Fig. 316 - Thickening and broadening of the gingival margins and papillae respectively in an attempt to crea'e a middle to advanced age appearance in the rum pew it km of the matrix of the denture. APPEARANCE Fig. 317. — Illustrates the shortening and rounding of the apex of interdental papilla and the widening of its base from youth (left) to advanced age ( right'. 4 3 2 .1 Fic. 318. - Variation in the gingival margin level of the anterior teeth. (The broken line is intended only for purposes of comparison.) gingival levels should be followed. The premolar and molar gingival level should also vary if a broad smile exists, the first premolar level being below that of the canine, the others being variations of that level. A denture having the gingival margins uniformly shaped and all at the same level with all the teeth set vertically and level with the occlusal plane creates the impres- sion of a row offence palings, thereby making the denture look artificial. Another reason for dentures appearing artificial is the manner in which the labial flange is shaped. Often this flange is a continuous arc from premolar to prcmolar and when light falls iipon it during a smile or laugh it gives a flat reflection devoid ofhjghlights and shadows (fig. 3 19), which is not tlieusua! occurrence with natural tissues. By contouring the labial flange highlights and shadow effect can be obtained, breaking up the flat reflection of the light falling on the denture (fig. 313). To do this, the labial area should be contoured to simulate the prominences caused by the roots of natural teeth. The canine roots are usually the most prominent and plumping in that CLINICAL DENTAL PROSTHETICS Fic. 3 rg - The smooth, flat, glossy surface of some dentures is the cause, \ er\ often, of the artificial appearance of a demure and is due to the t>pe of light reflection which occurs from such a surface region which follows the long axis of the crown of the tooth and the anatomical shape of a root enables the canine to be set prominently thus supporting the corner of the mouth and lip, thereby diminishing the extent of the naso-labial crease which often is so obvious in the edentulous patient. The root of the central incisor wall be less prominent than the canine and the lateral the least of all. 'When contouring the roots of the teeth the long axes of the crowns must always be followed and anatomical detail copied realistically. Models taken from natural dentitions as patterns are useful to have at hand when shaping the labial flange. The finished denture should be stippled, that is the reproduction of the minute creases and pits occurring in natural gum tissue which gives it that orange peel appearance, to break up further any large 7 oncs of light reflection (see fig. 313). The area covered by the contouring and stippling should be limited to the labial region and that part only of the buccal region likely to be exposed when the patient laughs. The reason for this being that a rough and uneven APPEARANCE 449 surface tends to collect food particles, whereas a smooth, polished surface is more self cleansing. The inference here is that stippling and gingival contouring should be diminished or possibly avoided in those cases where oral hygiene is poor. 7. The Smile Line and Arch Form The smile line related to the setting of the anterior teeth is a curve running through the incisal edges of the central incisors, sweeping upwards to the lateral teeth and thence to the tips of the canines. This arc is determined by the age of the patient, the more accentuated arc occurs in the young person since there is little attrition of the central incisors (figs. 320 and 321). As age F10. 320 - Illustralw attrition associated with varying age levels. (A) Youth Little or no attrition (B) Middle age Attrition beginning to involve the lateral (C) Old age Marked attrition of all teeth and attrition progresses the arc flattens until in old age it is almost a flat plane. This smile line can also be related to the sex of the patient bearing in mind the basic curved form associated with femininity. The amount of tooth showing during serious conversation is considered to be: In the young adult 2 mm. In middle age 1 1 mm. In old age o to - 1 mm. It is sometimes an advantage to show a little more tooth in the female than in the male at the various age levels to enhance the quality of femininity. The arch form of the anterior teeth should not necessarily be made to coincide with the resorbed alveolar ridge outline as this may have undergone considerable change, the features of the face should be studied and the arch made to harmonize 45 ° CLINICAL DENTAL PROSTHETICS Fic 331 - The smile-line of the incisal cilgcs of the anterior teeth vane* with age. Top. The upward sweep of smile line curve is seen piosdy in youth where no attrition ha* occurred m the incisor region Middle: In middle age the wear of the incisal edges flattens this curve. Lower: In old age this cun e mav be reduced to a flat plane bv marked attrition. with them. Generally it will be found that flat-faced individuals would be best suited by a flat arch and the pointed or sharp featured person suited to a tapering arch. In between will be the moderate arch curve adopted for the majority of individuals. A tapenng arch is most adaptable to the overlapping of teeth in the production of irregularities. 8. The Vertical Dimension The restoration of the facial appearance of the edentulous patient requires attention to three points. First, the correct placing of the upper anterior teeth; second, the restoration, by the correct thickness and positioning of the denture flanges, of the tissue lost during extraction and alveolar absorption; and thirdly, the establishment of the correct vertical dimension of the jaw relationship for the individual. Vertical dimension from the point of view of appearance is important as it is APPEARANCE 45 * Fig. 322. — Diagrammatic illustration of the facial musculature. If the upper anterior teeth are set too far back under (he ridge, thereby reducing the distance between the origins and insertions of the more horizontal muscles associated with the upper lip, the naso-labial fold is often accentuated; also such setting of the teeth allows the comers oF the mouth to Tall in, which may lead to angular cheilitis. Over-closure of the vertical dimension similarly reduces the distance between the origins and insertions of die more vertically running muscles, thereb> causing a compression of the facial musculature giving the patient the appearance of old age (ste fig 323). It may be a cause of angular cheilitis. CLINICAL DENTAL PROSTHETICS 452 related to the establishment of the correct separation of the origins and insertions of the muscles of the facial musculature. If these insertions arc brought too close together the muscles will tend to sag and bunch, conversely, if they arc too far apart the muscles will be stretched producing a strained appearance. For the muscles to be in their normal relationship the anterior teeth must be correctly positioned and the vertical dimension correct. The modiolus is then in its correct position and this tendinous node can effectively serve its purpose of acting as an anchor during contractions of certain of the facial muscles associated with expression and speech (figs. 322 and 323)- The final assessment of an appearance at the trial denture stage should always be made with the operator standing away from the dental chair and judgment made at varying distances ovcrclowd \rrtical APPEARANCE 453 to obtain the overall effect. Furthermore, a relative or close friend should, if possible, attend at this stage to give their con- sidered opinion. This often saves argument and ill-feeling between the operator and the patient after dentures have been worn for a few days and criticized by the family and close friends. Most people dread the thought of losing their teeth and hav- ing to be fitted with dentures, one of the reasons being the fear of having an artificial appearance with dentures. Such people will appreciate the care and thought given to producing a natural appearance and it is therefore a wise plan to have available examples and photographs of the types of naturalized effects and their appearance when in the mouth. If the patient does not discuss the question of appearance then this quesUon should be raised by the operator before any naturalized effects are introduced in the construction of a denture. Some people have a profound desire for their own conception of a perfect set of teeth, even though they carry the label ‘artificial’. Chapter XVIII PARTIAL DENTURES Assessment of the Partial Denture The previous chapters concerned the edentulous patient and those which follow deal with individuals who arc only partially edentulous, having one or more teeth missing from either mandible or maxilla or both. Dentures designed for such patients will vary considerably depending upon the number of natural teeth missing from the jaws and will range from those replacing only one tooth to others replacing all but one tooth. In order to be able to record missing teeth and to make reference to the remaining natural teeth it is necessary to have some easy means of notation. For this purpose the mouth is divided into four quadrants by a horizontal line representing the occlusal plane and a vertical line representing the mid- line. The eight teeth in eacli quadrant arc numbered from the front backwards, commencing with the central incisors, thus: Patient’s right Patient’s left 87654321112345678 A similar plan is used to denote the deciduous teeth, hut in this instance letters are used in place of numbers: edebajabede cdcba|abcde To denote individual teeth this chart is abbresiated by drawing only that quadrant in which the tooth or teeth to be recorded are situated; the upper left second premolar is noted thus 1 5, the lower right first molar 6|, the upper right lateral and upper left canine 2)3, and so on. It does not follow' that every’ individual who loses a natural tooth requires its replacements by means of a partial denture, sometimes a bridge is a better alternative and also there arc instances in which the replacement of lost teeth is considered inadvisable. Therefore the treatment for the patient who has 454 Fig. 324 - A partial denture. lost one or more natural teeth can be effected in one of three ways- (1) By fitting a partial denture. (2) By fitting a bridge. {3) By leaving the mouth as it is. Definition of a Partial Denture A partial denture is an appliance, removable bv the wearer, for the replacement of one or more natural teeth in the mandible or maxilla in which one or more natural teeth remain. It occupies more space than did the natural teeth which it replaces and is retained by its intimate contact with the mucosa and remaining natural teeth (fig. 324). Definition of a Bridge A bridge is an appliance which is fitted to two or more natural teeth prepared for, and restored by, inlays or crowns. It occupies no more space than did the natural teeth it replaces and it may be either permanently fixed in position or remov- able by the wearer (fig. 325). Fig. 325. - A bridge (constructed by Mr. C. Rosenstiel}. It must be pointed out that these definitions do not apply to American dental literature and skeleton dentures in England arc frequently called removable bridges in the U.S.A. The Function's of a Partial Prosthesis When a mouth is examined in which some natural teeth arc missing a decision has to be reached as to whether the replace* ment of the lost teeth by artificial substitutes, be it a partial denture or a bridge, will benefit the patient and if so what will be the most suitable type of restoration. To find the answer to each individual ease it is necessary' care fully to assess the advantages of a partial prosthesis against the disadvantages. A partial prosthesis functions in one, or more, of three ways. (1) It restores masticatory efficiency. Whilst it is an accepted fact that with the more highly civilized healthy peoples, living as they do on soft cooked foods, teeth are not necessary’ to maintain life, nc\erthclcss most PARTIAL DENTURES 457 people consider it essential to have sufficient tieth to be able to masticate normal food with ease. The effect of long-continued inefficient mastication on a healthy alimentary system is difficult to assess but in individuals already suffering from digestive troubles, or other debilitating conditions, masticator)* efficiency assumes great importance and its restoration may become a vital matter. {2) It restores appearance and speech. The commonest reason for a request b\ a patient for a partial denture is that of restoration of appearance. Many people will ignore the loss of the majority of their posterior teeth but demand the immediate replacement of a lost upper incisor. Speech is often affected by the loss of the upper incisor teeth so that the Iabio-dental and linguo-dcntal sounds, particularly, undergo loss in quality (see Chapter X). (3) It prevents collapse of the dental arch and oxer-eruption of teeth. Wien a tooth is extracted from a normal dental arch the teeth adjacent to it, unless prevented from so doing by the occlusion, tend to drift towards each other, thus reducing the width of the gap made by the extraction. This causes these teeth to lose contact with the teeth adjacent to them and food can then pack between them with consequent damage to the gums and increased liability to caries (see fig. 326). I.oss of' occlusion will often cause over-eruption and this, if gross, may mean the loss of that tooth (see figs. 327-331). Thus two or three teeth extracted from different parts of the mouth, if not replaced with a prosthesis, may in a few years lead to complete collapse of the dental arch which rapidly leads to further loss of teeth. One point which cannot be emphasized too strongly when dealing with arch collapse concerns patients of school- age. Immediate replacement of lost incisors is imperative as otherwise lengthy orthodontic treatment (often 1-2 sears) will be needed to regain the lost space. A delay of a few days in fitting a denture or space-maintaincr after the loss of an incisor may result in appreciable loss of space. Fig. 336. - 4[ has drifted backwards as a result of the failure to replace 65I with a denture. Fic. 329. - Space slightly o\er-res»ored by orlhodonlic treatment. Fig. 330. - Demure replacing jJ fitted and _/t allied to return to con-ect position. Ftc. 331. - / 12 extracted and / 1 lias been pulled backwards and downwards into space b\ powciful lower lip {six weeks after extraction). PARTIAL DENTURES 461 The Disadvantages of a Partial Denture (1) It can cause caries. By harbouring food debris in close coniact with the natural teeth a partial denture may promote caries. This will depend on several factors, chief of which arc: (а) The age of the patient. Up to the age of 25 years caries susceptibility is greatest, thereafter it tends to decrease. ( 5 ) The habits of the patient. If the patient is ^ ery assiduous in cleaning his teeth and denture then less damage is likely to ensue. (c) The design of the denture. This is all important because well designed dentures will cause far less damage to the mouth than those of thoughtless design (see Principles of Partial Denture Design). The caries which may result from denture wearing can be reduced by regular dental attention and partial denture wearers should always be advised of the necessity of regular dental inspection. (2) It can damage the supporting tissues of the teeth. In a healthy mouth the gum margins fit closely round the necks of the teeth, rising to a pointed crest between them; they are firm in texture and pink in colour. Their integrity is usually maintained in a well developed dentition because: (fl) Adjacent teeth are firmly in contact mesially and distally and, therefore, food cannot pack down between them and apply trauma to the gingival margins. (б) The buccal, labial, lingual and palatal surfaces of the teeth are convex so that food passing over these surfaces strikes the gum below- their free margin ( see fig. 332). Any alteration in Fra. 332. —Tlie arrows indicate the direction which the food takes as a result of the bulbous form of a tooth. 4^2 CLINICAL DENTAL PROSTHETICS this arrangement which causes force to be applied directly to the free gum margins will tend to push the margin nwav from its contact with the tooth and thereby damage it. Partial dentures may cause damage to the gum margins by: (a) Fitting too closely into the gingival trough and causing mechanical injury to it {see figs. 333-336). ib) Allowing food to pack down between the denture and the teeth. Food packed under pressure against the gingival margins will force them away from the teeth (see fig. 337) and will also, if allowed to remain in contact with tlic gingivae for any appreciable time, cause inflammation of the tissues resulting from the toxins formed by micro-organisms incubating in this nidus. Such damage to the gingival margins, if untreated, pro- gresses to involve the deeper supporting tissues of the teeth giving rise to periodontal disease and ending with the loss of the teeth. (3) It may loosen the natural teeth by leverage. Fin 335. - Sharp margin. Clasps which grip the teeth too tightly or indirect retainers (tee Chapter XXI) which arc badly placed may cause excessive stresses to be induced in the natural teeth. This will be dis- cussed at greater length in the section on design. (4) It can cause traumatic damage to the palate as described for full dentures on page 374 etseq. All the types of damage which can be inflicted by a partial denture arc shown in figs. 338, 339. CLINICAL DENTAL PROSTHETICS 4 C 1 FfC. 336. - Correctly relieved. Fig. 337. - (a) and (i) food packing (r) results of food packint' The advantages of dentures over bridges are: (,1) They can be constructed for any case, whilst bridges are confined to short spans bounded by healthy teeth and with a fairly normal occlusion. (a) They can be constructed of plastic material and there- fore more cheaply. PARTIAL DENTURES 465 Fic. 337(<0- _ Gaps between teeth and denture allow food packing. (3) They are more easily cleaned as are also the natural teeth in contact with them. (4) They are more easily repaired and in many cases can have additions made to them. (5) They do not normally involve the loss of natural tooth substance. The Advantages of Bridges The selection of the most suitable type of restoration for any given case cannot be fully discussed in a textbook on dentures. Instances occur in the foUowing chapters in which a bridge would be preferable to a partial denture but in order to avoid confusion such a possible line of treatment is not discussed. However, the following advantages and disadvantages of bridgework need consideration when deciding upon the treat- ment for any case requiring a prosthesis. 466 CLINICAL DENTAL PROSTHETICS PARTIAL DENTURES 467 The Advantages of Bridges over Partial Dentures ate: (a) They require no support from the mucous membrane and in fact in many instances they are not even in contact with it. (A) They only occupy the same space as the natural teeth which they replace (with the sole exception of the ‘Cantilever’ bridge), and therefore feel more natural in the mouth. (r) They will withstand greater masticatory loading than dentures, except when the latter are tooth-borne (Chapter XIX). (pe of denture suitable for a given case. (1) A tooth-borne denture can carry loads equal to those rvormally imposed on. the ua&uxaL teeth- (2) Sound natural teeth or a tooth-borne denture will impose a greater load on the opposing teeth during mastication than a tissue-borne denture, due to the pain threshold of the mucosa compressed between the hard surfaces of the bone on one side and the denture base on the other side. 47 2 CLINICAL DENTAL PROSTHETICS lingual portion joining the saddles is nearly always too nearly vertical and so transmits very little of the vertical loading. (7) An upper tissuc-bomc denture can usually spread the vertical load by covering at least some of the hard palate. A tissue-borne upper denture which only occludes with a tissue- borne lower denture does not need to cover any larger area than that covered by the sum of the lower saddles. (8) The larger the area covered by a tissue-borne denture the smaller the load per unit area for any given load. (g) The pressure required to penetrate any given foodstuff is inversely proportional to the area of the occlusal surface. This means in effect, that the narrower the teeth, bucco-lingually, the less muscular effort will be required to penetrate any given food. The problem of the tooth and tissue-borne method of transferring the load is a vexed one and frequently the subject of misconception. The opinion of the authors on this question is that it is impossible to construct a denture in such a way that any given vertical load is evenly distributed between the teeth and the mucous membrane. Further, where such an attempt is made an increasing load is placed on the teeth with the passage of time owing to alveolar absorption. Consider the case of the saddle in fig. 342. In order to obta’in an equal resistance to pressure by the mucous membrane as by the teeth the former must be compressed and distorted until further alteration in bulk and shape ceases and it will then act like a hard tissue and transmit any further load directly to the underlying bone. To obtain this result, a pressure of x lb. per inch will be required. At this exact pressure the occlusal rests must be seated on their respective teeth and thereafter any increased piessure will be evenly distributed, but at any- thing less than this exact pressure the denture will be entirely tissue-borne. If the occlusal rests are in contact with the teeth before this exact pressure is reached then the teeth are bearing more of the load than the mucous membrane, a condition which will inevitably arise when the supporting alveolar bone resorbs to the slightest extent. It is extremely unlikely that mucous membrane will tolerate this degree of pressure before the 47 4 CLINICAL DENTAL PROSTHETICS Fig. 343 - "Iwn a free end saddle ii fitted w ith an occlusal rest - the arrow show where the concentrations of stress develop. support. Such a state of affairs will overload the attachment of the premolar to the bone and probably lead to the early loss of this tooth and at the same time cause rapid absorption of the alveolar ridge at the distal end of the saddle. Hiller consideration is given to this problem in the appropriate section on actual design. Kennedy Classification A further classification of partial dentures in general acceptance in this country is that devised by Kennedy, and, when used in conjunction with the forementioned classification, enables a fairl> clear picture to be formed in the mind of the type of denture under consideration during a discussion on partial dentures. The Kennedy classification is based on the relationship of the saddles to the standing teeth and has four main groups with subdivisions where necessary. Class I. Bilateral free-end saddles posterior to the standing teeth (figs. 344 and 345). CLASSIFICATION OF PARTIAL DENTURES -175 Fic. 344. - Kennedy Class I upper. Fig. 345. — Kennedy Class 1 Class II. Unilateral frec-end saddle pv teeth (fig. 346). Class III. A bounded unilateral sadd> ; cither end (fig. 347). Class IV. A saddle anterior to the s&z-.~ CLINICAL DENTAL PROSTHETICS 47G F10. j|f> Kmnrd> Cb« It Fic. 317.- Krp.nrd) CUv* III. Fig. 349(a). - Kennedy Clan I modification I. 4/8 CLINICAL DENTAL PKOSTHETICS FlC. 3-10(4) - Krnnrdv Claw II mnclifiratinn I. Fit. 350, • Kcnncdv Claw III modification III. AH Classes, except Class IV, .arc subdivided by modifications, cacli modification denoting an additional saddle area. Thus an additional saddle area in Class I would be designated as Class I Modification I (fig. 349a). Two additional saddles would con* siilutc Modification II Class III, Modification III would be a basic unilateral bounded saddle with three addi- tional saddles, fig. 350, and so on. Class IV lias no modifications since if such occurred then it would fall basically into one of (be other Classes. Chapter XX THE COMPONENT PARTS OF A PARTIAL DENTURE In order to be able to design a partial denture it is necessary to know the parts from which it is built and the function of each. These parts are: (1) Saddles. (2) Connectors. (3) Direct Retainer (Clasps) (page 488). (4) Indirect Retainers (page 525). (5) Occlusal and Incisal Rests (page 530). 1. SADDLES A saddle is that part of a denture which carries the artificial teeth. It can be either tooth or tissue-borne, as also can separate saddles in the same denture (see fig. 351). 479 CLINICAL DENTAL PROSTHETICS 480 Dentures with tooth-borne saddles arc generally made In metal since a strong material is necessary for the construction of occlusal rests and the metal should be capable of being cast so that an accurate fit of the occlusal rest to its seating can be obtained. Dentures with tissue-borne saddles may be constructed either of metal or acrylic resin, but generally the latter for reasons of economy. The periphery of the denture in the saddle regions should always reach to the functional depth of the sulcus and should be modified only in relation to the appearance when in tlic mouth. 2. CONNECTORS A connector is that part of a denture which joins one saddle to another, or, a clasp or indirect retainer to a saddle, and may be classified as follows: (a) Palatal plates and bars, figs. 352 and 353. (A) Lingual plates and bars, figs. 354 and 355. jc) Labial plates and bars, fig. 356. ( Fio. 361. - Various types of clasp. cut areas both of the teeth and the solt tissue. In order to use these nndcrcuL areas it is necessary to know their precise limits; this requires the use of a surveyor. Reasons for Surveying A partially edentulous mouth has many undercut areas which result from : («) The naturally bulbous shape of the crowns of the teeth (%• 363)* (b) The fact that the long axes of the teeth arc frequently inclined at an angle to a vertical taken from the occlusal plane (fig. 364). (c) The soft tissue and underlying bone being inclined at an angle to a vertical taken from the occlusal plane (fig. 365). Rigid denture bases and the rigid parts of clasps will not pass 490 CLINICAL DENTAL PROSTHETICS Fig 36a - Note tariar deposited on ihis denture and die area on die left completely free (arrowed). This is due to the constant pressure of the tongue in that area to counteract the tilting loads applied to the incisor teeth. I Fig 363. - Illustrating how the naturally bulbous shape of a tooth produces undercut areas. B = the most bulbous part of the tooth. U = the undercut areas. Fig 364. - Illustrating how a slope of the long axis (L) of a tooth produces an undercut area. Fig. 365. - Undercuts in tuberosity region sun eyed for blocking out. into undercuts. (An undercut may be defined as an area which is out of contact with any vertical dropped from a given horizontal.) Therefore it is essential for the designer of a partial denture to be able to determine these areas on the model. The technique of this is termed surveying. 49 2 CLINICAL DENTAL PROSTHETICS Surveying is accomplished by holding a vertical marking device such as a graphite lead, in contact with the crown of the tooth and moving either the model or the lead so that the side of the lead draws a line around the circumference of the crown and its point draws a line, which is the projection of that on the crown, on to the model of the soft tissues {see iig. 366 a and 6). The area enclosed between these two lines is Fio. 366(0). -The basis of surveying. L = \ertical graphite lead. C = the line drawn by the lead on the crown of the tooth. M = the line drawn on the model. undercut. Similarly the soft tissue undercuts can be delineated by a line marking the maximum bulge, and its vertical pro- jection on to the adjacent soft tissue. Such undercut areas are frequently found in the tuberosity region and the lingual alveolar region of the mandible, particularly the molar area. If these soft tissue undercut areas are not indicated and eliminated the rigid denture base will not pass over the maxi- mum bulge and enter the undercut, except in cases where the undercut is slight and the mucosa covering the bone is thick and compressible. Surveyors Many different instruments are available for surveying but they all work on the principle of the vertical lead. They con- sist of a firm horizontal base, a mechanism which supports the marking device and enables it to be raised and lowered, and a table to which the model may, be attached, and which may be tilted so as to alter the horizontal axis of the model. The Fjc. 366 ( 4 ). - Lead of surveyor marking the most bulbous pan of the tooth and its projection on the model. reason for tilting will become apparent in due course. Such at. instrument is shown in fig. 367. The Value of Surveying a Model Surveying serves six purposes: (1) It enables undercuts to be accurately blocked out on the model prior to the processing or casting of the denture, so that the material of the base does not enter the undercuts and prevent the denture from being inserted { see figs. 368 and 369). Two methods are commonly employed for blocking out the undercuts on the model. (a) The area between the survey line on the tooth and that on the mucous membrane may be filled in with plaster of 494 CLINICAL DENTAL PROSTHETICS Fig. 367. - A Surveyor (King’* College Hospital Type). The lilting table contains a powerful magnet and the model lias an iron nng cast into its base; this obs fates the necessity for anv fixing agent such as plasticine. Fic. 368. - A denture which has been processed on * model, the undercuts of which were not blocked out. The denture will not go into place. THE COMPONENT PARTS OF A PARTIAL DENTURE 495 Fits. 365. - Undercut* correct!* blocked out, the denture goes into place. Paris, dental cement, wax, or composition, using the lines drawn by the lead as guides. ( 5 ) The area may be overfilled with hart! wax and this may then be trimmed, using a vertical cutting knife on the surveyor instead of a graphite lead (set fig. 370). Fic. 370. — Undercut* blocked out and being trimmed with knife on lurveyor. 49^ CLINICAL DENTAL PROSTHETICS This method, which is the more accurate, is useful when a duplicate model is to be used for casting or processing or when a wax pattern for a metal casting is removed from the model. (2) It marks the most bulbous part of a tooth which is to carry a clasp. This enables the technician to place the rigid part of the clasp above the undercut area, and the flexible arm, which does the work of retaining the denture, into the undercut (see fig. 371). tic 37i.-Sur\rv line* (brolen lines) enabling the pros- theiLM to select the correct type of clasp and place il accurately. As will be shown later, tilting of the model will affect the position of the survey line. (3) It will demonstrate undercut areas which can be used for the retention of the denture. Such utilization of undercuts requires the horizontal axis of the model to be tilted at an angle which is sufficient to eliminate the undercut in question and bring the side of the tooth adjacent to the undercut parallel with the lead of the surveyor (see fig. 372). The line of insertion of the denture is parallel with the side of the tooth adjacent to the undercut, and the denture will only go into place if inserted in this direction, because all other undercuts, which dcsclop as a result or tilting the model, are blocked out parallel with this line. Fig. 373 illustrates a more complicated case in which tilting the model has enabled 3 undercut areas (one mesial to the 1st molar, one mesial to the 1st premolar, and the labial undercut of the ridge) to be used for retaining the denture against vertical withdrawal. 498 CLINICAL DENTAL PROSTHETICS ric. 373. (a) Mode] lilted so as to eliminate undercuts. 1. Mesial 10 tst molar, a Mesial lo premolar. 5. Labial to ridge. 4. is the surveying pencil. 3. is the undercut which needs to be blocked out. (4) 1 1 enables those parts of the denture base which fit against the crowns of the teeth to be placed above the survey line, and therefore against the teeth. This ensures that the denture fits snugly against the tooth and does not leave a gap into which food debris may pack, a fault which is commonly seen in dentures which have been relieved empirically (see fig. 374). {5) It permits the operator to select, and design, a denture about one path of insertion so that all saddles and clasps are designed about this predetermined path and not as individual units. Frequently a path of insertion is determined by the under- no. 373 (b) Demure filled 10 ibu mode) along paih of tnicrtion shown by dolled lines will be retained against with- drawal along line of arrow by undercuts detailed above. cuts revealed during a preliminary survey of the abutment teeth of an anterior saddle. The tilting table often has to be adjusted to obtain the minimal undercut area in order to avoid unsightly spaces showing when the denture is in the mouth. (6) It enables the operator to measure, with undercut gauges, the depth, horizontally, of an undercut below the survey line marked on a tooth and thereby determine the type of clasp to be used and the material of which it is constructed. Undercut gauges are usually of 3 sizes having heads with lips of to- 20- and 30-thousandths of an inch (fig. 375). They are interchangeable with the vertical surveying lead and when in use the shank touches the tooth at the survey line and the rim of the head touches the tooth in the undercut. By using the various size heads the horizontal depth of the undercut can be measured anywhere between the survey line and the gingival margin and the clasp arm can be then placed 500 CLINICAL DENTAL PROSTHETICS b. The denture has been processed into the undercut and therefore will not go into place until it lias been trimmed aw a> by the amount indicated by the parallel bnes, anti when in place a gap is left, indicated by arrow, intu which food will pack {sit also fig. 3371/) Fig. 375.— Undercut Gauges. (a) Two sizes of head. (4) Illustrating the method used to determine the degree of undercut. in a, position appropriate to the material and type of clasp, A rigid type of clasp would not need the same depth of under- cut that would be required by a more flexible type of clasp. The Technique of Surveying These six functions of surveying have been described THE COMPONENT PARTS OF A PARTIAL DENTURE 5OI separately, for convenience, but in practice all six merge and are closely interrelated. Therefore, to show clearly how surveying is carried out, an actual survey will be illustrated on an upper model with the following teeth standing, 76 32 1 1 123 67. The model is fixed to the table of the surveyor with the occlusal plane horizontal and the lead passed round G 3 [ 36. The lines resulting from this survey arc shown in figs. 376, 377 , 378 - The conclusions drawn from this survey are as follows: (c too flexible. I »<*.. 403 («) (i>) I »o. s'l - i!^ arrwM v.lyh a mu»s «**f fin at it* tiffiioff it Intfrlftl, tf pt*f*nt - {4} * Vo[ *«> t»ln. i!f nmey hr*. 05 ««*-F l <}*■ virvry t.nr. -U L- 5 2 4 clinical Dental prosthetics Finally, clasps may be constructed of wrought wire, wrought plate or cast metal, and the following information is given regarding the advantages and disadvantages of each of these forms: The Physical Form of Clasps It is generally accepted that the retention of minute particles of foodstuff in contact with the enamel of the teeth is at least a predisposing cause of dental caries, and so it must be accepted as a fact that any form of clasp is potentially dangerous to the well-being of the tooth clasped. It follows, therefore, that any form of clasp should aim at creating the minimum amount of food stagnation, but as it is impossible for any clasp to fit so closely to the tooth as to prevent saliva laden with minute particles of food from lodging between it and the surface of the tooth, it also follows that the smaller the surface area the less dangerous the clasp. Further, it is most important that the inner surface of all clasps should be smooth and polished to the highest possible extent and kept so polished. This is particularly important in cast clasps for if the inner surface is neglected its naturally rough surface will become very foul. Round wire, making as it does only a line contact, is the cleanest form for a clasp followed by 4 -round wire and then plate. Cast materials are dependent on their surface area which can vary within wide limits. This line contact is often a disadvantage since it allows a rotation about that line, and further, unless there is a fair degree of undercut, a round wire may be unsuitable because of this very lack of surface friction. Round Wire (1) Cleanest. (2) Minimum friction. {3) Highly flexible. (4) Most easily constructed. (5) Probably most suitable for cases requiring several clasps. (6) Does not transmit every movement of the denture to the tooth, i.e. it possesses stress-breaking properties. THE COMPONENT PARTS OT A PARTIAL DENTURE 525 Half-round Wire (1) Physical characteristics between those of round wire and those of plate. (2) Used under the same conditions as round wire but the improved frictional grip does not necessitate so much undercut. Plate The use of clasps made of this material is not advised and the following is only included for comparison: (1) Definitely the worst fitting form and so, coupled with its area, the most liable to cause damage. (2) Flexibility reduced by its dimensions and the fact that it should be doubly concave, i.e. mesio-distally and occluso-gingivally. (3) Gives a very firm retention but special care must be taken that it does not impose a tilting strain on the clasped tooth. (4) Can be used as an indirect retainer, but as this will be bound to put a tilting strain on the tooth it should only be so used in cases where there is no possible alternative. (5) The most difficult type to construct. Cast (1) Accurately fitting. (2) Easily varied in thickness, form and taper. (3) Easily thickened to act as an inelastic brace. (4) Can easily include an occlusal rest. (5) Can be cast as an integral part of a gold denture or cobalt chrome base. (4) INDIRECT RETAINERS An indirect retainer is so called because it retains in position some part of a denture remote from itself. It works on the principle of the counter balance {fig. 405). In the illustration AB represents a bar suspended off centre at G. Point B will drop and A will rise until equilibrium is attained. If, however, point A is prevented from rising by placing an immovable block, D, above it, then point B cannot drop. This principle 5? 6 CLINICAL DENTAL PROSTHETICS A C--_C Fjg. 405 can be employed in partial dentures whenever a free*end saddle is so long that it cannot he retained adequately by the clasp fitted to the abutment tooth. A typical example is shown in fig. 406. The denture is retained directly by clasps C, C, the free-end saddles being long tend to fall away from the tuber* osities. In addition they exert excessive leverage on thc'pre- THE COMPONENT PARTS Or A PARTIAL DENTURE 527 molar teeth carrying the clasps. If an extension, A, of the saddles of the denture is made on the opposite side of the line joining the clasps, and this extension rests on the palatal sur- faces of the canines and incisors, then provided that the reten- tion supplied by the clasps is adequate to retain the dentures against normal dislodging forces, the saddles cannot drop unless the indirect retainer for A forces the incisor* and canine teeth out of position; provided these teeth are firmly rooted this will not happen. Indirect retainers are best made of metal, preferably cast so that they fit the teeth accurately. They should be placed as shown in fig. 407. In this position they are low enough on the Fig. 407 tooth to prevent excessive leverage developing, and any ten- dency for the retainer to slide down the tooth is resisted by its cingulum. Indirect retainers may be made of plastic material as part of a tissue-borne denture as illustrated in fig. 408. An occlusal or incisal rest, a connector or a saddle may act as an indirect retainer provided its position is such that it is on the opposite side of the line or lines joining the direct retainers or cfasps to that part which requires to be retained. Fig. 408 illustrates how various parts of a denture may act as an indirect retainer. The more remote the position of the indirect retainer from the line joining the points of direct retention the more efficient be- comes the indirect retainer. That shown in fig. 4o8(£) is more 5 28 CLINICAL DENTAL PROSTHETICS Tig. 4081,5) THE COMPONENT PARTS OF A PARTIAL DENTURE 529 W Fio. 408. - Thrc; examples of ihc principles of indirect retention. The dotted lines indicate the fulcrum of clasp retention in each ease and that part of the denture on one sjde of the line indirectly retains that part on the opposite side and vice versa. If as illustrated only two clasps are employed there is inevitably a tendency for the denture to rocl. about the fulcrum of retention a nd in case ( 4 ) this could be prevented by clasping 5/ as well as 7/5 also if no saddle existed in 4/ region then an occlusal rest placed on 4/ would act as an indirect retainer. efficient in action than that shown in fig. 408(c) since the parts being retained are approximately equidistant from the line of direct retention, whereas in C the palatal bar is closer to the line of direct retention than the points to be retained. The po : nts to bear in mind regarding indirect retainers are these: (a) They can be used only on firmly rooted teeth. (£) They should be borne by as many teeth as possible, to reduce the possibility of moving teeth by the application of excessive force. (c) They can only function in conjunction with a direct retainer, i.e. a clasp or clasps. 53 d CLINICAL DENTAL PROSTHETICS ( 5 ) OCCLUSAL AND INCISAL RESTS Partial Denture Support The forces acting on the occlusal surface of a partial denture must ultimately be absorbed by the bones of the jaw. If the area of tissue covered by the denture is sufficiently large, these forces will be absorbed by the soft tissues and transmitted to the bone in the same way as occurs with full dentures. However, if the area of a partial denture is small, as often happens, the force applied to unit area of the soft tissue will be above its tolerance, and pain and ulceration will ensue. In these cases, therefore, other means of transferring the occlusal loads to the bone arc required. This is done by supporting the denture cither wholly or partly on the natural teeth which, being designed to transmit forces of a high order to the bone, suffer no damage if their supporting tissues arc sound and the denture properly designed. The parts of the denture which transmit the loads to the teeth arc called rests. The main function of rests is to transfer some, or all, of the masticatory loads to the natural teeth. In addition they may serve two other important functions: (a) They act as contact points and thus prevent food packing between the denture and the natural tooth. (b) They retain clasps in their correct position and prevent them sinking and pressing into the gingival tissues. Rests are of three types: occlusal, cingulum, and incisal. 1. Occlusal Rests ( see figs. 409, 410, 411) These are made to fit into a mesial or distal fossa on the occlusal surface of a tooth and to be satisfactory they must comply with the following requirements : (a) They must fit the tooth accurately in order to minimize the collection of food debris beneath them and also to locate them correctly in relation to the tooth. (i) They must be strong enough to bear all normal mastica- tory loads without deformation. THE COMPONENT PARTS OF A PARTIAL DENTURE 531 Fjc. 409 (r) They must not ‘gag’ the occlusion. In the majority of cases a certain amount of preparation of the tooth surface is necessary in order that room may be made for the rest and the shape of the occlusal surface may be favourable for it {see fig. 413). Fig. 410. — A case with sufficient occlusal rests to spread the load. Fig, 412. — Upper illustration shows mesial and distal fossae and fissures in teeth. Lower illustration shows rest seat preparations in mesial and distal fossae. Note how the fissures have been removed and the preparations are smooth and saucer shaped. TIIE COMPONENT PARTS OF A PARTIAL DENTURE 533 This preparation is carried out with carborundum stones or diamond points and does not damage the tooth as it is rarely necessary to penetrate the enamel. If such penetration is necessary an inlay must be fitted to support the rest or caries will occur. If an opposing cusp is ground to make room for a rest the exposure of dentine is unimportant since it is a self- cleansing area and hence unlikely to be attacked by caric> (see fig. 412). ( d) They must transmit the stress down the long axis of the tooth as this is the only direction in which the load can be increased without damage to the periodontal membrane. (e) They must be at right angles or less to the long axis of the tooth otherwise the pressures of mastication will tend to force the denture away from the tooth or rice versa. An undue load will be placed on the resilient portion of a 534 CLINICAL DENTAL PROSTHETICS clasp which is made in conjunction with an obtuse ancled occlusal rest. 2. Cingulum Rests (see fig. 414) These are made to rest on the palatal or Ungual surface of front teeth. They are usually unsatisfactory' rests because the shape C Fic. 414 . (a) Cingulum rest- (t>) Cingulum rest from the side. (f) Inasal rest. of the palatal surfaces of most teeth are not suitable to carry a rest. This will be appreciated from a study of fig. 415. If an occlusal load A is transmitted to the rest it will in turn transmit it to the tooth. This load Mill then be resohed into two loads B, which is broadly at right angles to the rest, and C which is broadly parallel to it. It will be appreciated that at least half the load which the rest is supposed to transmit to the tooth is actually devoted to forcing the rest down the tooth, and must be absorbed by the underlying soft tissue. THE COMPONENT PARTS OF A PARTIAL DENTURE 535 3. Incisal Rests (see fig. 414(c)) These are mainly used in cases where only six lower front teeth are standing. They tend to be unsightly and are only used when no other rest can be provided. The use of indirect retainers and occlusal rests is discussed further in the next chapter. MATERIALS FOR PARTIAL DENTURE BASES 537 Advantages of Aciylic Resin (1) It simulates the appearance of natural gum to a greater degree than vulcanite or metal. {2) The technique is simple and quick and requires little special apparatus. (3) It can be used for all cases although it is not necessarily the best material for the majority. (4) It can be used for the whole denture, including the teeth. (5) It forms a chemical union with acrylic teeth thus giving a very strong attachment. (6) Repairs and additions can easily be made. (7) It is light in weight. (8) It is easy to keep clean. Disadiantages of Acrylic Resin (1) The design of dentures is greatly limited by the weakness of the material. (2) Its resistance to fatigue is low, and it frequently fractures after a few months in the mouth. {3) It has a tendency to warp during dc-flasking, as the stresses induced in the material during processing are released. This may lead to inaccuracy of fit. It also warps when re-cured for repairing. (4) Its softness leads to rapid wear when used for posterior teeth in contact with natural ones. It is also easily abraded by cleaning with a stiff brush. Advantages of Vulcanite (1) It is very accurate and warps to a much lesser degree than acrylic resin. (2) It is highly elastic, very flexible and possesses a high resistance to fatigue. It is thus capable of passing into and out of small undercuts and rarely fractures in use. (3) It can be repaired without distortion. {4) The technique is simple and quick. 538 CLINICAL DENTAL PROSTHETICS Disadvantages of Vulcanite (i) Its appearance is very unlifelike and this is the main reason why it has been so largely displaced by acrylic resin. (a) Its surface hardness is very' low and in use it soon loses its polish and, in consequence, is difficult to clean. Vulcanite is unlikely again to be used as a sole base material, but in view of its many' superior physical properties it is some- times very* valuable as the main base material if acrylic resin is used in conjunction with it as a facing for those parts of the denture which show. Metal Alloys Advantages of Metals (l) Their superior physical properties enable them to be used in thin section and this factor allows great latitude in the design of the denture. It is also appreciated by the patient, as partial metal dentures take up little space in the mouth. {2) Their resistance to fatigue is great and fracture in the mouth is uncommon. (3) Their high thermal conductivity' enables normal sensa- tions of heat and cold to be appreciated. Disadvantages of Metals (1) The techniques of their fabrication are time-consuming, require a high degree of skill and need special apparatus. {2) Their appearance does not simulate the natural gum. (3) Additions and repairs cannot be performed easily because these operations entail either soldering or welding and in the majority of cases before either can be performed the teeth need to be removed from the denture. (4) They may cause electrolytic action if the denture is in contact with a dissimilar metal filling. Individual Metal Alloys Casting Alloys ( Yellow Gold) This is an excellent material for use in constructing any type of partial denture. MATERIALS TOR PARTIAL DENTURE BASES 539 Its advantages are: (1) If cast into an investment which gives compensatory thermal expansion for the casting shrinkage, the final denture is accurate. (2) Due to the fact that all properly constituted gold alloys contain from 12-15 P er cent of copper, they are susceptible to heat treatment. The value of this is that the casting may be softened for the final adjustment of clasps, and then given the hardening heat treatment which endows the denture with: (fl) A high proportional limit ; thus enabling it to resist all normal stresses brought to bear on it, in and out of the mouth. (b) A modulus of elasticity which is sufficiently high to allow the connectors to be made thin, but not so high as to rob the clasps of adequate flexibility. (3) Any additions, such as wrought clasps or metal backings for porcelain-faced teeth, may easily be soldered on to the main base. Disadvantages of Gold: The only true one is its high cost, although some individuals consider its colour to be a disadvantage. Palladium Silver Alloys ( White Golds ) Advantages: (i) They produce accurately fitting dentures'. {2) They arc, like yellow gold, susceptible to heat treatment but the final mechanical properties are not so satisfactory as yellow gold. (3) Attachments can be added easily by soldering. (4) Are cheaper than yellow gold although the cost is still considerable. Disadvantages: (1) Alloys containing a high silver content tend to turn black in use due to the formation of silver sulphide. 54° CLINICAL DENTAL PROSTHETICS (2) The high rate of occlusion of oxygen and hydrogen tends to produce porosity. (3) Care must be taken, and the manufacturers 1 instructions rigidly adhered to, when heat treating these alloys or brittleness will result. Coball Chrome Alloys Advantages: (1) They arc so far the only completely corrosion-resistant base metal alloys which can be cast. (2) The denture is an accurate fit, provided a special com- pensator)' investment is used for its casting. (3) Compared with the precious metal alloys they are extremely cheap. (4) The majority of them have a satisfactory proportional limit and a high modulus of elasticity. (5) They can be added to by soldering or welding. Disadvantages: (j) They require a considerable amount of special apparatus for their fabrication. (2) They take longer to trim and polish than other metal allo>s. (3) Their flexibility is low. (4) They are not susceptible to heat treatment. (5) They lack the ‘kindliness’ of gold, and are extremely hard. Wrought Alloys Gold or palladium silver alloys and stainless steel can be fashioned into partial dentures by swaging between special dies and counter dies. Since the mechanical properties of wrought metals are superior to those of cast, due to the difference in grain structure, swaged dentures can be made even thinner than those which are cast. MATERIALS FOR PARTIAL DENTURE BASES 541 The main disadvantages of wrought metal denture bases are: (1) The fit is far less accurate than with castings. {2) Skeleton dentures are very difficult, if not impossible, to fabricate. {3) Strengthening of individual areas can only be done by soldering or welding on an extra thickness of metal. Stainless steel for many years has been the main wrought alloy used in dentistry but its usefulness for partial dentures has been greatly limited by the difficult technique, which requires a special hydraulic press and a welding machine. The Composition of Cobalt Chrome Alloys No detailed specifications of the alloys available in this country arc published. As is the case with the gold alloys the individual chrome alloy's on the market differ slightly from each other but their general composition is roughly within the range of either (a) Chromium 30% or ( b ) Chromium 30% Cobalt 60% Cobalt 30% Molybdenum 5% Nickel 30% Molybdenum 5% The other 5% is made up by small quantities of Carbon, Iron, Manganese, Silicon, Aluminium, and Beryllium which arc added to modify the properties of hardness, stiffness and ductility. It is the large chromium content which produces the corrosion resistance exhibited by these alloys and this is their main claim for use in dentistry. The Mechanical Properties of Cobalt Chrome Alloys The mechanical properties of these alloys in the cast condition given as an average are as follows: Proportional Limit 60,000 lb./in.* This figure means that the material is strong enough to resist any normal stresses it is likely to encounter in dental use and compares favourably with many casting golds. Modulus of Elasticity 30 X 10* lb./in. 4 This indicates that a large force is required to produce a 54 2 CLINICAL DENTAL PROSTHETICS small deformation of the material, in other words it is stiff. Such a property is desirable in such parts of a partial denture as connectors, rests and indirect retainers. Taken together with the proportional limit, however, it means that the alloy possesses a low flexibility which is a disadvantage in clasps. Brinell Hardness 250-320 This means that the material is a little difficult to polish but once a lustre has been obtained it will remain during long use in the mouth. The higher figure of 320 is above the hardness of tooth enamel which is on an average about 250. Percentage Elongation 3-4 per cent This figure refers to the ductility of the material and gives an indication of the amount of adjustment to which it may be subjected once cast. 3-4 per cent is not high but some gold alloys in the heat treated condition are lower than this. Specific Gravity 7*9 For a given volume its mass is less than half that of gold and it may, therefore, be considered a very' light material. The Application of these Properties to Denture Design (1) The cross-sectional area of connectors such as lingual bars, palatal bars and continuous clasps may be less than that usually employed when using a gold alloy. This is due to the greater stiffness of the material and not to its greater strength. (2) The dimensions of clasps should be as small as possible, never greater than British Dental wire gauge B and they should taper towards their tip. The reasons for this arc.' (a) The flexibility of the material is low and its stiffness great. These factors vary' with the square of the cross-sectional area and if this is kept as low as possible and further reduced by tapering the tip of the clasp less force is required to insert and remove the denture and the tooth will not be gripped too rigidly. (fc) If the clasp arm is placed too deeply into a se\cre undercut it will have to travel outwards a great distance to MATERIALS FOR PARTIAL DENTURE BASES 543 pass over the most bulbous part of the tooth and then a corres- ponding distance inwards to grip the tooth. As the flexibility is so low, the force required to drive the arm outwards this distance may be greater than the proportional limit of the material will withstand and consequently it will bend. (3) Clasps must be accurately positioned and accurately cast because the percentage elongation is insufficient to allow of much adjustment. Chapter XXII THE BASIC PRINCIPLES OF PARTIAL DENTURE DESIGN The requirements of a partial denture may be summarized as follows: (r) It must spread the forces which will act on it evenly over the supporting tissues to a degree within their physiological limit and be adequately retained in position in the mouth during all normal functional movements. {2) It must prevent the dental arch from collapsing by preventing the teeth from drifting or tilting into edentulous spaces. It must also cause the minimum amount of damage to either soft or hard tissues. (3) It must maintain the health of previously unopposed teeth by restoring their function and preventing their over- eruption. (4) It must restore masticator)' efficiency and appearance and be comfortable to wear. To satisfy all the above requirements it will be apparent that the designer of a partial denture must take into account many things, satisfy many needs and solve many problems. The group of problems which it is intended to deal with here is restricted, for simplicity of explanation, to the method of designing a denture so that it may satisfactorily* transmit to the supporting tissues the loads which will be applied to it in function in such a manner that the tissues them- selves do not have to bear loads above their tolerance and the denture itself w ill remain stable under all normal conditions. In order to produce a design which satisfies the above condi- tions the simplest manner in which to proceed is to divide the complex loads which arc applied to a partial denture into the four basic component loads which are: (1) vertical occlusal, (2) lateral, (3) antero-posterior, (4) vertical dislodging^ Then, taking these one by one, ensure that the denture is designed to transmit each to the supporting tissues without 1 Partial Denttats, Osborne. J. and Lammic, G. A , Blackwell Scientific Publica- tions, First and Second editions. PRINCIPLES OF PARTIAL DENTURE DESIGN 545 overload and at the same time ensure that it is adequately braced against movement by the load. The first question the designer asks himself therefore is: How are the vertical occlusal loads to be transmitted? When deciding whether a given denture is to be tooth-borne, tissue-borne or tooth and tissue-borne the following points should be kept in mind. (a) A fully tooth-borne denture wall resist the greatest loads and provide the most efficient mastication. (b) If the denture is opposed by natural teeth, tooth-borne support is desirable, because, under these circumstances the load applied to the denture will be at the maximum. (c) A denture can only be fully tooth-borne by molar and prcmolar teeth, with sound or adequately restored crowns, supported by well-formed roots whose long axes are almost vertical and arc embedded for an adequate distance in healthy bone (the information to enable one to make a decision on this aspect will be available from the clinical examination). Canines and incisors cannot alone provide sufficient support for a tooth-borne saddle, due to the inclination of their palatal or lingual surfaces, unless suitable inlays arc fitted with occlusal rest scatings prepared in them. Taken together as a group of three or more teeth, however, they may be able to support a denture without the necessity of inlay preparation. (d) If the occlusal rests arc to transmit effectively to the teeth the loads imposed on the denture there must be sufficient room for them to be adequately seated. Study models will show if there is sufficient room for the rests with the teeth in occlusion and if there is not room it can frequently be made by grinding the opposing tooth. The scat should always be prepared for the rest in the enamel of the tooth which is going to carry it and obviously any such preparation must be completed prior to the taking of the working impressions. (e) If the saddle areas are extensive, that is where more than two natural teeth are missing from any saddle, it will probably be necessary to design the denture so that the loads applied to it are transmitted via the soft tissues. Under these circum- stances as great an area as possible of the ridge must be covered so as to reduce the load applied per unit area. If the denture-bearing area of the tissue-borne denture is considered inadequate to withstand the anticipated vertical loading, such for example as some instances of the Kennedy Class I lower in which there is a narrow, hnife-like ridge with shallow sulci, it will be necessary to reduce the vertical load applied during mastication by: (1) reducing the bucco-lingual width of the artificial teeth, (2) leaving ofT the last tooth from the saddle. The problem of the tooth-tissue borne method of transferring the load is a vexed one and frequently the subject of miscon- ception and the opinion of the authors on this question has been discussed in Chapter XIX. A few examples of individual cases will be given to illustrate how a decision is arrived at with regard to resistance to vertical loading. Except where the outline is completely black the folloiving diagrams are not intended to show the shape of the finished denture but are purely concerned with illustrating the approximate areas which will receive and resist the loads which are applied to the denture. The direction of the applied load and the area resisting it is delineated thus: Occlusal loads Lateral loads Anteroposterior loads Tortional loads Mixed loads PRINCIPLES OF PARTIAL DENTURE DESIGN 547 and the artificial teeth are drawn with a thick line to differentiate them from the natural teeth. Fig. 416 represents a partially edentulous maxilla of the Kennedy Class III type with 65I56 missing. It is opposed by a full natural lower dentition. The crowns of 74(47 arc sound {the word ‘sound’ as used in this book means that the crown of the tooth is either caries free or has been satisfactorily con- served) and the roots are supported for more than two-thirds of their length by bone. In a case of this type the choice of method for supporting the vertical loads is by occlusal rests on 74! 47. A tooth-borne denture will enable the patient to chew forcefully, it will not tend to sink or be driven into the mucous membrane and the rests themselves will prevent food being forced down between Tic. 416. - On the right the approximate area of the E nodonl.nl membrane available for supporting the occlusal sdi u illustrated. Compare this with die area available on the left if tissue support only is enlisted, see also fig. 418. 54 ^ CLINICAL DENTAL PROSTHETICS the denture and the abutment teeth on to the gingival margins. Before a final decision can be made that occlusal rests can be used on this case the models must be examined in occlusion to see, either that room exists for the rests or that it can be pro- vided by limited grinding of the opposing teeth. Rest seats must be prepared in the fossae of the teeth carrying the rests. If the supporting bone in a case of this type is considered on examination of the X-ray negatives to preclude the carrying of the additional load of the denture, that is, if the roots of the abutment teeth, or any' one of them, is supported for less man one-half of its length by r bone, or if the negatives show that the bone is undergoing rapid absorption (s« fig. 417) then the saddles will have to be tissue-borne and they should be outlined on the models to cover as large an area of the ridge as possible so that the vertical load applied to the denture is spread as widely as possible. In a case such as this, tissue-bomc saddles as a Fig. 417(a). - Illustrates a lower premolar which is quite unsuitable for carrying a rest: the bone is undergoing rapid absorption and a rarefying osteitis is present in the bone supporting the distal surface of the root. PRINCIPLES OF PARTIAI DENTURE DESIGN 549 . 4*7- (4) Although this premolar is only partly supported by bone that immediately surrounding* the root is showing a condensation of bone (condensing osteitis) which results in providing extra support for the tooth, and if this tooth is subjected to extra stress by placing a rest on it the bone will react favourably. Tile surface of the edentulous ridge is not very suitable to support a Ussue-bome denture because it shows evidence of rarefaction and the surface is rough in spite of the fact that the last tooth was extracted over two years ago. means of transmitting the vertical load are very definitely inferior to occlusal rests as will be appreciated by' studying fig. 418 which shows a comparison between the surface area of the periodontal membranes of the 1 47 available to support a tooth- borne saddle and the surface area of the mucous membrane which will support a tissue-borne saddle 1 . In addition, the mucous membrane will, in function, distort unevenly and therefore only some of its surface will actually transmit the load and finally absorption of the ridge will further upset the equilibrium. 1 Watt, D M., MacGregor, A. R , el at. (1958) Dtrtlal Pract. 9 : a {see also fig. 418) 550 f CLINICAL DENTAL PROSTHETICS Fib. 417. (e) Although the lower molar u leaning me* tall) ii i< veil supported by bone which shows signs of eondcasation anteriorly. It would be wise to place the rest posteriorly on this tooth so that the titling movement of the load would be reduced. Nevertheless, in many cases of this kind, tissue-borne saddles do provide a satisfactory foundation for transmitting the vertical load and such dentures arc frequently worn for many years with satisfactory results. Fig. 419 illustrates a case similar to fig. 41 6 with more extensive lateral saddles, 654)456 being missing. Here the decision between tooth- and tissue- borne saddles is not quite so simple to make. The 7I7 can certainly carry rests, but with three teeth, on each saddle instead of two, as in fig. 416, the extra load which the 7] 7 can be called upon to bear will be proportionately heavier and unless the roots of these teeth arc long and \cry well supported in dense bone such extra load is likely to cause loosening and tilting of the teeth. Further, 3I3 by themselves are not suitable teeth for carrying occlusal rests because the palatal and cinguiar slopes of these teeth form an inclined PRINCIPLES OF PARTIAL DENTURE DESIGN 551 Hg. 417. (J) The roots of this molar arc short but the bone supporting it is dense and although it is tilted medially 11 should be capable or supporting a distally placed rest. The surface of the edentulous ridge in both (e) and (d) is smooth and covered with a thin layer of cortical bone and should suppi rt a tissue home saddle with little absorption plane and reference to fig. 415 will show that a vertical occlusal load applied through a rest to such a surface is resolved into a force along the surface and one at right angles to it and if the angle of inclination of the palatal surface is steep then most of the occlusal load is converted into a force tending to drive the rest o(T the tooth. If, as in a ease like this, the posterior movement or the saddle which such a force will engender is resisted by the buttressing effect of the mesial surfaces of the upper second molars then an additional and unfavourable backward load is applied to these already over- loaded teeth. If it is decided that the canines must carry rests then proper inlay preparations must be made in them with rest seats designed to transmit the vertical loads straight down the long axes of the canines. In a saddle of the length of that Ho. 417. (t) The bone supporting bolh these tcetlj is raref) ing rapidly and there u no e\idenee of condensation; the surface of the bone in the edentulous area shows no cortical bone and these teeth are quite incapable of supporting occlusal rests. A tksue-bome saddle would not fit for long because rapid absorption of the ridge would probably; occur. These teeth are best extracted. (No illustrations are given of ideal bone support for teeth carrying rests or for ridge surfaces carrying tissue-borne saddles as these are self evident. The above figures show X-rays of cases in which doubt may exist.) shown in fig. 419, however, it is considered that this method of using the rest would overload the attachment of the canine and such techniques are best reserved lor saddles carrying only two artificial teeth. If the six front teeth in this case are considered as a group, and the denture carried up on to the cingulac of each tooth as shown in fig. 420 then possibly sufficient resistance to occlusal loading will be provided to make the saddles truly tooth-borne. If the slope of the palatal surfaces of these teeth is steep, how- ever, an even greater backward thrust of the denture is likely to be engendered. In addition, a continuous rest of this type will, of necessity, cover the palatal gingival margins of these teeth which is detrimental to the health of these tissues. The PRINCIPLES OF PARTIAL DENTURE DESIGN 553 Fic. 418. - The black shape immediately below the model represents the area of mucous membrane available to support the occlusal load of a tissue-bome saddle replacing 1 56 Compare this with the black shapes below the molar and prcmolar teeth with represent die areas of the periodontal membranes of the I47 which are available to support the occlusal load of the saddle if it is tooth-borne (After Watt and MacGregor it al ) Kennedy bar can be used to overcome this difficulty but patients frequently dislike the narrow, raised ridge which such a bar presents to the tongue and finally a large majority of patients will present such a deep overbite that room is rarely available for either a continuation of the plate to provide a continuous rest or a Kennedy bar. From the foregoing considerations it will be obvious that in the majority of cases a tissue-bome denture, as illustrated in fig. 419, will be the method of choice, the shaded areas in the diagram being the saddle areas which will resist the occlusal loads. Fig. 421 illustrates, in the lower jaw, a similar case to fig. 419. 554 CLINICAL DENTAL PROSTHETICS PRINCIPLES OF PARTIAL DENTURE DESIGN 555 Here the remarks regarding the effect of a continuous rest on the inclined lingual surfaces of the lower front teeth apply even more forcefully because the angulation of the inclines of these teeth is steeper as a general rule than those of the upper teeth. Fig. 422 illustrates a case with three saddles. Here the choice of support of vertical load is complex. Following the above reasoning the right saddle carrying 7654) should be tissue- borne, the front saddle also should be tissue-borne unless properly prepared inlays are to be inserted into the 3J1. The left hand saddle, however, carrying only [56 and having as abutments the J 47 which can well support the two artificial teeth, can be tooth-borne. If it is considered desirable to make this saddle tooth-borne, perhaps because it is opposed by natural teeth in the lower jaw, then the connector between this saddle and the other two must be of such dimensions that it allows the slight but definite differential movement between it and the other two tissue-borne saddles. 55 ® CLINICAL DENTAL PROSTHETICS Tic. 422. - 7634 21 1 are twsue-bome and I56 are tooth- borne The connector between the tooth and tissue-bome saddles (C) must be of such dimensions that 1% hile being ngid it still allows a slight dilTerential mo\ ement between the two classes of saddle otherwise as the tissue-borne one sinks slightly on chewing the tooth-bomc saddle will rise. In such cases as are illustrated in figs. 423 and 424 the prob- lem of choice of the method of transmitting the occlusal load is simplified because these saddles are so extensive that they can onl> be tissue-borne. The second question: How are the lateral loads to be resisted? These loads are imposed during the lateral movements of the mandible during normal mastication; they can be varied by tooth form, tooth area and the balance of the articulation, but they cannot be eliminated. Even if the teeth are left out of any possible contact a lateral load can still be applied through the medium of intervening foodstuff - . The greatest lateral stresses arise where there is cuspal interference and when this is absent the lateral stress is proportional to the occlusal area. PRINCIPLES OF PARTIAL DENTURE DESIGN 557 55^ CLINICAL DENTAL PROSTHETICS The tissues which will resist the lateral movements of the denture and transmit them to the underlying bone are the lingual and palatal surfaces of the teeth and also their buccal surfaces if clasps incorporating a bracing section to the func- tional arm are fitted. The lingual and palatal and buccal surfaces of the ridges also provide a considerable surface area for resisting the lateral loads applied to a denture. If, however, both teeth and soft tissues are used to resist lateral movements, then, for the same reasons as given in the section on occlusal loads, it is likely to be the teeth which will carry the major portion of the load. This should always be bome in mind when designing a denture. To illustrate this question of resistance to lateral loading and to enable the designer to understand the method of deciding how the denture in question is to be shaped to resist the lateral loads which are applied to it, three examples will be considered Figs. 4125 and 426 represent a Kennedy Class I upper, having well formed ridges, with deep sulci and a deep, broad palate. The observations made when studying such a case would be that the well-developed ridges of the saddle areas would pro- vide good resistance to the lateral movement of a denture dur- ing mastication to either the right or left sides. Therefore it would be unnecessary to utilize the standing teeth to resist lateral movement and an adequate tissue coverage for the denture to resist lateral movement only might be as illustrated in figs. 425 and 426. Figs. 427 and 428 represent a Kennedy Class I upper with poorly developed ridges, shallow sulci and a broad, flat palate. The inference from this example is that there is little expectation of resistance to lateral movement to be gained from the buccal and palatal surfaces of the ridges and therefore the natural teeth would need to be utilized for such resistance. The denture outline to resist lateral movement in this case might be as shown in fig. 429. In fig. 427 the denture makes no contact with the palatal aspects of the teeth whatsoever and relies entirely on the ridges for support against lateral movement, whereas in fig. 429 all the palatal surfaces of the teeth are covered by the denture to brace PRINCIPLES OF PARTIAL DENTURE DESIGN 559 The shaded area is the tissue available for resist mg lateral loads applied to this case Ho. 425. - In plan. Tig. 42G. - In coronal section. It against lateral movement and additional bracing is also obtained from the rigid parts or the clasp arms. Fig. 430 represents a Kennedy Class III Modification I type of case, either upper or lower with 65(56 missing. The abut- ment teeth arc sound and well supported by dense bone and under these circumstances, the occlusal load being taken by the rests, the lateral loads can safely be accepted by these teeth and resistance to lateral movement can be gained by carrying clasps and reciprocals on the buccal and palatal aspects of these teeth. In addition, of course, the occlusal rests themselves 560 CLINICAL DENTAL PROSTHETICS Ptc. 428. - In coronal section. being seated in rest seats in the teeth, will provide quite a marked degree of resistance to the lateral loads. If, in a case such as this, the abutment teeth are not well supported by bone, it may be necessary to transmit the lateral load entirely by means of the palatal and buccal slopes of the ridges and in this case a decision will have to be made as to whether the resistance afforded by these surfaces is adequate to provide sufficient resistance to lateral movement on the same lines as the decision was made in the cases illustrated in 425 and 427. If the lateral slopes of the ridges are capable of resisting the load then a possible outline might be similar to that illustrated in fig. 426. This shows how the broad coverage of the lateral slopes of the ridges will enable adequate resistance to lateral movement to be provided. If the lateral and palatal slopes of the ridges are considered inadequate to provide PRINCIPLES OF PARTIAL DENTURE DESIGN 561 Fig. 4^0. -The risht side illustrate* the approximate area available if the »dd!c canning the second premolar and fir»t molar rely on the trnh to rout lateral load* The left side i! lustra 10 the approximate area available If the *oft tunic* are cmplojrd. 562 CLINICAL DENTAL PROSTHETICS sufficient resistance to lateral loads then it may be necessary’ to carry the denture round the palatal aspects of all the standing teeth to gain sufficient resistance as illustrated in fig. 429. In some cases where there is a doubt in the designer’s mind as to whether the buccal and palatal slopes of the ridges arc adequate to resist lateral movement and yet he feels it is un- necessary' to carry' the denture round all the standing teeth a compromise may be made by carrying the denture round some of the standing teeth and sharing the load between the slopes of the ridges and the standing teeth, as illustrated in fig. 431. All that has been said about the types of designs for these upper cases is, of course, applicable to lower cases of similar type, in these instances the lingual and buccal surfaces of the ridges are the tissue surfaces which arc capable of resisting lateral movement of the denture. Frequently, however, it is found in lower cases, that the ridges arc less well developed than the uppers and often, therefore, greater support must be enlisted from the standing teeth. When designing a denture to resist lateral movement, care must be taken that no individual tooth is subjected to too principles of partial denture design 563 severe a load neither in a direct lateral direction nor in the form of a rotary one. The ease illustrated in fig. 432 is an example of how this possibility may develop. The ease illustrated is a Kennedy Class I lower Modification I, the left saddle being completely edentulous and the right side being edentulous except for the isolated lower second prcmolar. The ridges arc absorbed and the sulci arc shallow and if the denture is designed with a lingual bar as illustrated then the tendency of the denture to move side wap is resisted almost entirely by its contact xv ith the isolated standing prcmolar. In addition there is a tendency for the saddle on the left hand side to move backwards during mastication and to inflict a torsional strain on this isolated tooth. In such a ease the resistance to lateral movement must be increased by carrying the denture around the lingual aspects of all the lower standing front teeth, as illustrated in fig. 433 and also by placing a bracing type of clasp on the lower canines. Fic. 433 -If 3(3 arc clasped and the denture is carried round the lower front teeth the area available for resisting the lateral load is greatly increased. The Third Question How are the antero-posterior loads to be resisted? These, like the lateral loads, arc best resisted by standing teeth, though the)- may be resisted by the soft tissues via a large labial flange or, less satisfactorily, an extension of a lower denture on to the anterior slope of the ascending ramus. Groups of teeth provide the most satisfactory resistance to the antero-posterior loads applied to a denture because they give mutual support to one another. An isolated tooth is rarely satisfactory to resist these loads, with the possible exception of a sound, \\ ell-rooted second molar and it must be remembered that the tooth anterior to a free-end saddle is an isolated tooth if it is used by means of a clasp to resist a backward load, whilst it may still be one of a group of teeth which is capable of resisting a fonrard ioad. Again the use of illustrations will probably clarify this question of the resistance to antero-posterior loads. Fig. 434 represents a Kennedy Class III Modification I case in which there are two bounded saddles. The resistance to the anterior movement of this denture is provided by the distal surfaces of the canines which themselves are supported by the four incisors and provided these teeth are adequately supported by bone they are quite capable of resisting all the anterior loads which are likely to be applied to this denture during function. The posterior loads arc similarly satisfactorily resisted by the mesial surfaces of the first molars, which themselves are buttressed again by the second molars. In this type of case no real problem arises with regard to the antero-posterior type of movement. The main problems of designing a denture to resist antero-posterior movement are concerned mainly with the Kennedy Class I frec-cnd saddle type of dentures and the Kennedy Class IV anterior saddle dentures. Fig. 435(a) illus- trates a Kennedy Class I lower. The resistance to anterior movement of this saddle is adequately provided by the distal surfaces of the canines which, as in the previous illustration, arc 566 CLINICAL DENTAL PROSTHETICS Fic 435(a ). - Illustrating the approximate area provided by the 3?|a3 for resisting anterior movement and b\ the ascending rami for resisting posterior movement. If the canines are clasped with bracing clasps some of the area provided by the teeth vrill resist posterior movement also. well buttressed by the other standing teeth. The resistance to posterior movement, however, can only be achieved by carrying the distal extension of the base of die denture as high up the ascending ramus as the case will allow. Fig. 435(e) shows how Fig 435(6). - Plenty of area to resist anterior loads but little to resist posterior moseroent. If 4]_is clasped some of the area available for resisting anterior movement can be utilised to resist posterior loads. PRINCIPLES OF PARTIAL DENTURE DESIGN 567 finishing the saddle short distaliy provides no resistance to posterior movement, whereas fig. 435 (£) shows how the exten- sion of the base of the saddle up on to the ascending ramus will provide a resistance to posterior movement. If, in addition, clasps are fitted to the lower canines with satisfactory bracing action, these also will provide additional resistance to posterior movement. Care must be taken, however, that these clasps are not so rigid that they tend to place abnormally high loads on these teeth. Fic. 435(f). - No resistance to posterior movement at all because the heels of lh«* denture are finished short of the ascending ramu and there is no clasp round the 4J. In Kennedy Class I uppers there is no anterior slope of the ascending ramus such as exists in the lower to buttress the den- ture against posterior movement. Fortunately, however, most of the loads applied to an upper denture during mastication are in a forward direction due to the upward and forward move- ment of the lower jaw and the inclines of the cusps and in these cases the distal surfaces of the canine teeth and the anterior slope of the palate provide adequate resistance to anterior movement. The Kennedy Class II type of case sometimes presents con- siderable problems in relation to resistance to posterior move- ment and here it is sometimes necessary to provide really rigid bracing by carrying a rigid connector round to the other side of the mouth and firmly clasping the standing natural teeth on that side. Although this is likely to produce a torsional move- ment of these teeth, provided they are well rooted and two or sometimes three of them are clasped, they are usually capable of standing up to the torsional load thus applied to them. If, in 568 CLINICAL DENTAL PROSTHETICS addition, the lower canine on the side of the saddle is also clasped and the denture carried round it and up on its lingual surface, and in addition the posterior aspect of the saddle is carried on to the ascending ramus, adequate resistance to pos- terior movement can be provided. The carrying of the bracing connector round to the opposite side of the mouth also provides considerable resistance to lateral movements applied to this denture. The area resisting labial loads is illustrated in fig. 436. Kennedy Class IV cases present one or two special problems. In the case illustrated in fig. 437 the posterior movement of the denture, which is slight, can be adequately resisted by the mesial surfaces of the upper canines and the anterior move- ment of the denture can be resisted by the anterior slope of the palate and possibly by carrying the denture around the palatal aspects of the canines. Pure antero-posterior movements, however, are not the only ones to which this type of denture is subjected, because when food is incised there is a torsional strain applied to the denture and the anterior ridge and some of the surface of the palate acts as a fulcrum. This action is Fig. 436. -Areas asailable for residing antero-posterior loads in Kennedy Class II type of case A lingual plate carried round the lower anterior teeth would be even better. PRINCIPLES OF PARTIAL DENTURE DESIGN 569 illustrated in fig. 438. This torsional action frequently produces considerable damage to the ridge and anterior surface of the palate, producing quite rapidly, a flabby and inflamed mucous membrane with loss of supporting alveolar bone. It is, therefore, particularly important in this type of case that some means of spreading this torsional strain is incorporated in the design of the denture. The fitting of a labial flange will do much to reduce torsional stress by providing a broad bearing surface anteriorly and thus helping to resist the tilting load applied to the denture, as illustrated in fig. 439. Further resistance to the torsional stress may be gained by clasping the last molar teeth and this will provide a very definite resistance to the torsional movement of the denture because the anterior ridge is acting as a fulcrum and the application of the load is not very far from the fulcrum, whereas the application of the resistance by a clasp placed on the last molar is a long way from the fulcrum and therefore its mechanical advantage is great 57o CLINIC A L DENTAL PROSTHETICS Fulcrum. Fic. 439- - Illustrating how ihc fitting of a labial flange to a Kennedy Class IV' denture produces a larger area for resisting the torsional loads applied during incising. {see fig. 4-}0). In some cases it is impossible to put a labial flange on this type of case because the patient’s appearance would be spoiled bv its presence. When it is necessary to ‘gum-fit’ the anterior teeth a clasp or clasps must be fitted as far posteriorly as is practicable in order to resist torsional movement. The Fourth Question How arc the vertical dislodging forces to be resisted? Forces which tend to dislodge a denture are: ( to shading). opposed by a natural lower 7] and therefore greater lateral loads will be applied by this tooth than if the saddle were opposed by artificial teeth only, it will be wise to gain extra resistance to lateral movement by carrying the denture round the palatal surfaces of 4(6. Resistance to lateral loads will be gained automatically by the fitment of the denture against the mesial surfaces of 1I3. The rating given to resistance to the lateral movement of this denture in general is ‘good’. Decision Three Resistance to antcro-postcrior loads now need to be con- sidered. In the lower denture the right saddle presents no problem because it is buttressed against forward movement by the distal surface of thc4| which is itself supported by 32 J, and against backward movement by the mesial surface of 7}. This is a 5^6 CLINICAL DENTAL PROSTHETICS solitary' tooth but is double rooted and in this case adequately supported by bone. The resistance to forward movement of the left saddle is adequately provided by the distal surface of the [4. The resistance to posterior movement of this saddle is rated only ‘fair to poor’, however. It will gain some resistance to backward movement from the keying effect of the right saddle between 74I but the torque action occurring through the long lever arm of the connector will place a considerable strain on these teeth and additional resistance should be provided by extending the saddle up the ascending ramus and placing a clasp around [4". This additional resistance to posterior movement will probably produce a rating of ‘fair’ for this saddle and a note should be made that the cusps of the teeth on this saddle should be low so as to reduce the tendency for the saddle to be pushed back- wards. The antero-posterior movement of the upper denture is now considered. The left saddle is adequately braced between the j36 and the mesial surface of the upper |3 will also resist posterior movement to some extent. The distal surface of^J will resist forward movement of the saddle on that side and it is well supported by 321]. The anterior slope of the palate will also resist forward movement. In this case the resistance to backward movement of the right saddle is questionable and should be rated only ‘fair’. But there is a keying effect against backward movement of this saddle provided by both the anterior and the left saddles and taking into account the fact that the tendency of an upper denture to move backwards is less than a lower such keying effect is con- sidered safe in this case. It is still advisable, however, to make a note that the cusps of the teeth of this saddle should be low in order not to provide inclined surfaces for the development of posterior forces. Decision Four The question of resistance to withdrawal forces now needs to be considered. In the lower denture clasps have been placed on 74J4 for the virtue of their bracing action against lateral movement. These PRINCIPLES OF PARTIAL DENTURE DESIGN 587 clasps will also provide retention of the denture. The centre of their retentive action will fall much nearer the right saddle than the left, however (sir page 518; and the resistance to with- drawal of the distal end of the left saddle, which is a long one, will be rated ‘poor’. It must therefore be considered whether it is necessary to place a continuous rest or carry the base of the denture on to the lingual surfaces of the lower front teeth to act as an indirect retainer to resist this movement and in this case, as the left saddle is very long, it would be considered necessary to do this. The resistance to withdrawal of the upper denture is simpler. There is considerable frictional retention gained by the close fit of the denture against mesial surfaces of 1 ) 3 and I36 and in addition a large area of the palate is being covered by the base of the denture to resist lateral and antero-posterior move- ment and therefore adhesion and tongue control will markedly assist retention. It is not therefore considered necessary to put clasps on this denture and its resistance to withdrawal forces is rated ‘fair’. Decision Fiie The final decision of the designer is to produce the complete outline of the denture, make up his mind in relation to the types of connectors and come to a decision ivith regard to the coverage or freeing or the gingival margins. In the lower denture the question devolves itself into deciding whether the connector between the tu o saddles shall be a cast lingual bar with a cast indirect retainer that leaves the gingival margins uncovered or whether the acrylic plate shall be carried round and up the palatal aspects of the lower front teeth and in the upper den- ture whether to carry the acrylic of the palate round all the standing teeth or leave the 321I7 free.-The need to secure firm resistance to lateral movement and adequate indirect retention of the left saddle dictates the use of a lingual plate as the lower connector. The question of cost decides that it shall be made of acrylic. The 321 (7 are relieved from coverage by the denture because they show evidence of gingival damage { see fig. 446). The following pages carry illustrations of a variety of denture designs based on the principles discussed in this chapter. CLINICAL DENTAL PROSTHETICS FlO. 4|6(«). PRINCIPLES OF PARTIAL DENTURE DESIGN 589 KENNEDY GLASS I PARTIAL DENTURES 59 * Figs, 447(0 and b). - Mela l Lingual Plate. Class I. Modification O. Ordinal loading. Partly tooth-borne on the premolars and anterior teeth, partly tissue-borne in the saddle regions. The lingual plate is presented from sinking into the gingisal margins by being tooth-borne on 4I4 ( 4 ). The saddles are attached to the plate by stress-breaking clasps (n), thus reducingjhe tilt action nbicb otherwise would be applied to the 4I4 by saddles rigidly connected to the lingual plate and carrying occlusal rests and clasps Lateral loading. Resistance is shared by the alveolar ridges, anterior teeth and clasped prrmolars. Advantageous in cases with shallow ridges. Antero-postmor loading. Movement u resisted by the clasps and collets of the lingual plate. The finished denture would be extended to give maximum buttress against the retromolar pad region. I'ertual displacement. Mo\ ement is resisted by direct clasping of the 4I4 and by indirect retention from the lingual plate resisting the upward mm ement of the distal aspect of the saddles through the line of direct retention across the premolars. By using a stress-breaking design it is possible to have the denture partly tooth-borne which is contra-indicated in designs of rigid unit construction as a nit action is introduced across the Occlusal rests and the lingual plate lifts out of contact with the anterior teeth. 592 CLINICAL DENTAL PROSTHETICS KENNEDY CLASS l PARTIAL DENTURES Vic. 448(a). — Metal Lingual Plate and Bar. Claw I. Modification O. Occlusal loading. Tissue-borne saddles (frcc-end). Lateral loading. The well dc\ eloped ridges are considered adequate support as the saddte areas arc of short span. .ln/ere-/x>j/(Tier loading. The distat aspect of the collets of the “3(3 rest against the mesial surface of the 414 resisting distal jnosement and arc assisted in this by correct coverage of the retromolar pads. Vertical displacement. By surveying the model with an anterior downward tilt the undercut zones of the distal surfaces of the 5J5 may be used combined with the frictional grip of the Lingua! plate against the mesial surface of the 3 (3, Lingual ban pass the 54 (4‘> to clear their gingival margins and to overcome the lingual inclination of the second pre- molars. An anterior plate is used instead of a bar to give greater stability. Ftc. 448(A). — A line diagram of an acrylic design incor- porating a wrought linguaf bar. The Jfs are cfasped to provide direct retention and to aid resistance to posterior movement. A less expensive denture. 594 CLINICAL DENTAL PROSTHETICS KENNEDY CLASS I PARTIAL DENTURES 5D5 Fig. 449(a). - Metal Partial Upper Demure with a Posterior Palatal Bar. Class J. Modification J. Occlusal loading. Tissue borne saddles (frec-endb Lc'rral loading. Movement lateral!) ts resisted b> 4)34 , the saddle of |a and clasping of the 4I4. Provided that the is firmly supported by sound alveolar bone thw tooth should support the lateral load adequately. The ridges arc of average size and will aid in the resistance to movement. .4 n tcm-j-ostcrior loading. Movement will be resisted on the left side bv the |a saddle and [4 clasp. The right side relies mainly on the clasping of the 4] but receives support from |z saddle and clasped (4. Vertical duflarrir.mt. Direct retention from the clasped 4]+ and indirect retention of the posterior saddles b) the anterior saddle and vice versa This design minimises the coverage ol gingival andpa latal mucosa. The posterior bar is kept reasonably 'vide in order that it may be suitably thin thus avoiding the thicker narrow bar which sometimes cannot be tolerated by the patient. Fig. 449(6). — A line diagram of an altemativ e design using acrylic.' The main difference is in the coverage of palatal mucosa which patients often state causes Io«s of taste and temperature sensations. 59^ CLINICAL DENTAL PROSTHETICS KENNEDY CLASS I PARTIAL DENTURES 597 Fig. 450(a). - Metal Lower Lingua! Bar and Continuous Clasp (Kennedy Bar). Class I. Modification None. Orchid/ loading. Partly tooth-borne on the premolar and anterior teeth and partly tissue-borne on the saddle areas Tliis design cannot be solely tooth-borne as occlusal loading must compress the mucosa of the sadd/e areas thereby causing the denture to tilt across a lin e joining the occlusal rests Such mo\ cment, when the 4I4 arc clasped in addition, will lt3\e an adverse effect on these teeth as they will be moved with the denture movement, and wall soon be lost. Lc.'nal loading. Well supported against lateral movement by the clasping of 4I4 and the continuous clasp in addition to ridge support. AiUro-poslertor loading. Movement resisted by the clasps, continuous clasp and the correct coverage of the relromoiar pads. Vertical displacement. Direct retention by clasping 4I4 - Indirrct retention of the saddles by the continuous clasp placed on the cingulae of the anterior teeth This design is not adv ised as too great a stress is applied to 4(4 due to the tilung movement of the denture across the occlusal rests and encircling clasps. Also many patients com- plain of annoyance from the lingual bar and continuous clasp, which also may collect food debris Fic. 450(A). — A line diagram of an alternative design using acrylic. This illustrates the all-acr\tic lingual plate denture. It is tissue-borne as opposed to being partly tooth-borne but is otherwise similar in its resistance to the displacing forces. Direct retention is obtained by clasping 4T4. and indirect retention by the lingual plate. This should be relieved along the gingival trough line by carefully trimming and polishing the finished denture in that area. 596 CLINICAL DENTAL PROSTHETICS KENNEDY CLASS I PARTIAL DENTURES 597 Ftcs. 430(a). - Metal Lower Lingual Bat and Continuous Clasp (Kennedy Bar). Class I. Modification None. Occlusal loading. Partly tooth-borne on the premolar arid anterior teeth and partly tissue-borne on the saddle areas This design cannot be solely tooth-borne as occlusal loading must compress the mucosa of the saddle areas thereby causing the denture to tilt across a hu e joining the occlusal rests Such movement, when the 4)4 are clasped in addition, will hate an adverse effect on these teeth as they will be moved with the denture movement, and wall soon be lost. Lateral loading. Well supported against lateral movement by the clasping of 414 and the continuous clasp in addition to ridge support. Antero-posterior loading Movement resisted by the clasps, continuous clasp and the correct coverage of the relromolar pads Vertical displacement. Direct retention by clasping 4I4 - Indirect retention of the saddles by the continuous clasp placed on the cingutae of the anterior teeth. This design is not advised as too great a stress is applied to 4T4 due to the tilting movement of the denture across the occlusal rests and encircling clasps Also many patients com- plain of annoyance from the Ungual bar and continuous clasp, which also may collect food debris. Fig. 450(4). -A line diagram of an alternative design using acrylic. This illustrates the all-acrylic lingual plate denture. It i* (issue-borne as opposed to being partly tooth-borne but is otherwise similar in its resistance to the displacing forces Direct retention is obtained by clasping 4I4, and indirect retention by the lingual plate. This should be relieved along Die gingival trough line bv carefully trimming and polishing the finished denture in that area 598 CLINICAL DENTAL PROSTHETICS KENNEDY CLASS I PARTIAL DENTURES 591 Fig. 451. — Metal Partial Upper Denture. Class I. Modification I. Occlusal loading. Tissue-borne. Lateral loading. Shallow ridges and a rather shallow palate call for maximum support from the standing teeth hence the complete coverage of all the standing teeth. .bitero-postmor loading Resistance to movement on the right side is obtained from clasping the 3I with additional support from the saddle of [4 There is no problem on the left side as the saddle of (4 presents movement. Vertical displacement The {5 can be clasped adequately but there is only slight retention from ^J, therefore use is made of the distal undercut of the 3I by suitably tilling the surveying table. Some degree ~of indirect retention is obtained by fixing the plate on to the anterior teeth, and the maximum use is made of the factors of adhesion and cohesion by covering the maximum denture bearing area Retention of the denture was considered to be the main problem. An identical design could be carried out in acrylic demure base material but metal was used in this instance because of a history of continual fracture of a previous acrylic denture. KENNEDY CLASS II PARTIAL DENTURES 603 Tig. 453(a)- — A Lingual Bar T/ssue-bomc Partial Denture. Class II arch. Modification II. No tooth opposed the right free end saddle and for this reason this denture saddle is omitted from the design. Occlusal loading. The two saddles on the left side are tissue- borne because no additional loading could be placed on the anterior teeth due to their slight ‘looseness’ and considerable aheolar absorption around |a. The I58 are considered inadequate for the support of the occlusal loading which would be placed upon the four artificial tecth_of the left saddles. An occlusal rest has been placed on 5I to prevent the plate around the 65J from sinking into the gingival margins. Lateral loading. Movement resisted by the well for med ri dges of the left saddles and by the clasps around 6 [58! ■f!«fcro-/>o5tfrwr loading. No problem of mosement since the saddles ha\ e abutment teeth either end. Vertical displacement. Direct retention by clasps around 6|j8. Since the I5" is clasped the saddles on the left side act as indirect retainers to each other. A bar is used to join the two left saddles in preference to a plate since the lingually inclined presents a marked undercut zone. Fig. 453 (i). — A design of an acrylic denture for a similar case in which the (356 are missing. Being tissue-borne gingival damage may be expected as alveolar absorption occurs in the saddle regions. For this reason frequent inspection of the mouth should be carried out and tissue changes noted and dealt with followed by relining, or making a new denture. 6oo CLINICAL DENTAL PROSTHETICS KENNEDY CLASS II PARTIAL DENTURES }><;. 452(4). — Meta I Lingual Phtc Toeith-bomc 1 -ourr Denture. CLw II. Modification I. Occlusal loading. The left saddle is tooth-borne w ilh occlusal rests placed on I57, the right saddle is parti) tooth-borne b\ the occlu'al rest on the 51 and partly tissue-borne b> the saddle liaving a stress breaking connector. Lateral loading. Movement resisted by the clasps 5)57 and the lingual plate collets around the anterior teeth. .IiTfi/frwr loading. The bounded saddles of the left side present no problem, the right saddle being prevented from moving by the collets around 54T and the clasped 5). Vertical displacement. Direct retention from clasps and indirect retention from the lingual plate. The greater part of the denture can be tooth-borne thereby preserving the health of the gingival tissues. The lingual plate is considered advisable as little room exists between the gingivat margins and lingual sulcus for a lingual bar, and alto the plate aids retention. Fto. 452(4). - A line diagram illustrating an alternative and less expensive design incorporating a wrought lingual bar. a lootn-bome left saddle and a tissue right saddle This combination is possible since the long lingual bar accommodates the movement of the right saddl e d uring tissue compression under occlusal loading. The 5T57 are clasped for direct retention but this design loses the indirect retention of the lingual plate denture. The lateral and antcro-posierior loading are misted in a manner simitar to that in design (u). 602 CLINICAL DENTAL PROSTHETICS KENNEDY CLASS II PARTIAL DENTURES 603 FlC. 453(0). — A Lingual Bar Tissuc-bome Partial Denture. Class II arch. Modification II. No tooth opposed the nght free end saddle and for this reason this denture saddle is omitted from the design. Occlusal loading. The two saddles on the left side are tissue- bomc because no additional loading could be placed on the anterior teeth due to their slight ‘looseness’ and considerable aheolar absorption around |a. The I5U arc considered inadequate for the support of the ocdusal loading which would be placed upon the four artificial teeth of the left saddles. An occlusal rest has been placed on 5]" to present the plate around the 65! from sinking into the gingival margins. Lateral loading. Movement resisted by the well for med ri dges of the left saddles and by the clasps around 6(58. Antero-posterior loading. No problem of movement since the saddles have abutment teeth either end. Vertical displacement. Direct retention by clasps around 6(58. Since the T5 is clasped the saddles on the left side act as indirect retainers to each other. A bar is used to join the two left saddles in preference to a plate since the linguaUy inclined jj presents a marked undercut zone. Fig. 453 (ft). - A design of an acry lic denture for a similar case in which the I356 are missing. Being tissue-borne gingival damage may be expected as alveolar absorption occurs in the saddle regions For this reason frequent inspection of the mouth should be earned out and tissue changes noted and dealt with followed by relining, or making a new denture. 604 CLINICAL DENTAL PROSTHETICS Tic. 454(d). Fw. 454W. KENNEDY CLASS II PARTIAL DENTURES Fto. 454 (h)- -Acr> he Partial Upper Denture (line diagram). Class II. Modification I. Occlusal loading. Tissue-borne. Lateral loading Movement is resisted by clasping 4I7 and b> the anterior saddle of |i_and the collet around the 4J. Antrro-hosknor loading. Movement is resisted by the collet and clasp around lhc_£|, a small flange on the anterior saddle and the collets and clasp or ]6j. Vertical dtsplaennent. Direct retention from the clasps around the 4I2 and indirect retention of the posterior saddle by the anterior saddle and vice versa, since each falls well outside the line of direct retention between the clasped 4(7. Adhesion and cohesion become a factor in retention due to the large area covered by the denture. In surveying a model for such a design it may be possible to tilt the surveying platform in a manner which enables the palatal undercuts of the [67 to be used for retention purposes. This is an asset when the buccal survey lines of J67 are unfavourable for placing clasp arms. As many gingival margins as possible have been left uncovered to minimize tissue damage by the denture. Fig 454(6). -A line diagram illustrating a design which could be used when a metal denture is contemplated It cannot be fully tooth-borne since there exists a free -end A lliin metal plate is preferred to the thicker cross-section required lor narrow palatal bars The loading forces are resisted in a similar manner to those described in (a), as also are the displacing forces, except for loss of adhesion and cohesion due to limited coverage of the palate. The interdental clasp which is placed between the [56 acts as an occlusal rest and prevents the plate sinking into the gingivae of those teeth. This design minimizes palatal coverage which is a point frequently welcomed by patients. 6o6 CLINICAL DENTAL PROSTHETICS KENNEDY CLASS III PARTIAL DENTURES 607 Fig. 455(a). - Cast Lingual Bar Partial Lower Denture. Class III. Modification I. Occlusal loading. Tissue-bome. This is necessary since both 7 J7 are somewhat loose and show bone degeneration on X-ray examination, otherwise it is an ideal case for a full) tooth-borne denture. Lateral loading. Mo\ ement is resisted b> adequate ndge form and by the collets and clasps around the 4I4. Antrrio-pastrrior loading. No problem presents since there arc abutmet teeth cither end of the saddles. Vertical displacement. Mo\ ement is resisted by the clasps around the 4I4 and by the use of the mesial undercuts of the 7I7 obtained by a suitable inclination of the surveying platform. A similar denture can be constructed with a wrought lingua! bar and all aery lie saddles and collets. Fig. 455(6). -Cast Lingual Bar Partial I/>wcr Denture. Class III. Modification I. Occlusal loading. The right saddle is tooth-borne and the left saddle is tissue-bomc. This saddle is not made tooth borne since it is considered inadvisable to place the occlusal loading of the two artificial molars upon the one natural molar and one premolar. Lateral loading.’ Movement is resisted by the alveolar ridge and the clasps around 86(58. Antcro-posterior loading. No problem exists as the saddles are bounded either end. Vertical displacement. Direct retention n obtained by placing clasps in a quadrilateral form making indirect retenuon unnecessary so that a lingual bar can be used as a connector, which, being long, accommodates for the movement between the tissue-borne saddle under occlusal load and the stable tooth-borne saddle. This design permits the maximum clearance of gingival margins. A completely tissue-bomc denture with acrylic saddles and a wrought lingual bar could be an alternative and a less expensive denture, the saddle outlines remaining the same. 6o8 CLINICAL DENTAL PROSTHETICS KENNEDY CLASS III PARTIAL DENTURES Fig. 456(a). — Metal Palatal Bar. Partial Upper Denture. Class III. Modification IT. Occlusal loading. Tooth-bome upon 532I358 Lateral loading. No problem exists as clasp placing necessitates sufficient reciprocals to resist lateral movement adequately. Ant/ro-posterior loading. The bounded saddles present move- ment. Vertical displacement Direct retention by placing clasps in a triangular pattern using 4I58 The palatal bar is made wide and therefore it can be thinner in cross-section than the narrow type of bar There is no anterior connecting bar since this may interfere with speech. Fig. 456(4). -A line dugram illustrating a similar case where the denture is constructed in acrylic with cast occlusal rests on the 5I57. The occlusal rests and clasp arms may be unit construction in chrome cobalt. Resistance to the various loadings is similar to that described in (a). Retention is also based on the triangular placmg of the clasps Palatal coverage needs to be greater because of the weaker denture base material. The same design could be used as a tissue- borne denture by omitting the occlusal rests. The gingival margins would probably then be subjected to trauma Fjg.4570)* KENNEDY CLASS III PARTIAL DENTURES 6l Tic, 457(a). - Metal Partial Upper Denture. Claw III Modification II Occlusal loading. Tiwue-bome. This cannot be tooth-borne since the quadrilateral placing of occlusal rests necessary in such a case cannot be achieved as there is only a lateral incisor at the left comer of tlic arch, and a tooth-bomc denture would subject this tooth to loo great an individual load. lateral loading. Movement resisted by ihc anterior l»unded saddle and the posterior collets of the denture Anttro-posterhr loading As with a Class 111 case no problem exists as the saddles arc bounded mesially and distally. Vertical displacement, A suitable lilt of the surveying platform makes use of the mesial undercuts of the 4I2 for anterior retention whilst the 7)7 are clasped to retain the posterior pjrt of the denture. no. 457(A). -A similar type of case in which the denture is all acrylic using no clasps. Retention is by adhesion and cohesion and frictional grip betwren the many saddles an 1 the standing teeth Careful surs cy ing is necessary in this instance together with extremely accurate blocking out of the undercut areas as denturr trimming at the chairside results in spaces between the collets and the teeth leading to food packing, canes and gingiwus. Fic. 458(a). - Metal Partial Upper Denture. Class III. Modification II. Occlusal loadmg. Tissue-bome. The saddles arc too extensive for this denture to be tooth-bome. Lateral loading. The anterior saddle plus the collets and clasps of 8)7 provide sufficient resistance to lateral movement. Anlero-fmteru'r loading. No problem exists as the posterior saddles have abutment teeth either end. Vertical displacement. The surveying table is inclined to allow the mesial undercuts of 1J3 to be used for retention, the CI7 being clasped to retain the posterior part of the denture. The connecting bars have been made wide so that they may be suitably thin. This type of design is sometimes called a skeleton denture. The outline for an acrylic denture would be similar but the palate would be covered. KENNEDY CLASS IV PARTIAL DENTURES 613 Fic. 458 lb). -Acrylic Partial Upper Denture Class IV. Occlusal . loading. Tissue-borne. Maximum palatal coverage without encroaching upon the gingival margins. Lateral loading. Bounded anterior saddle prevents movement laterally. Antero-posterior loading. Anterior movement prevented by the slope of the anterior part of the palate and by the con- tact with the palatal aspect of 1 13 Posterior movement is prevented by incorporating a labial flange in the ]ia saddle Vertical displacement. Retention is by frictional grip against the abutment teeth of the saddle, by adhesion and cohesion, but mainly b> the patient developing tongue control of the denture during the incising action. The labial flange assists in this by counteracting the forward tilt during this incising action Tliis design is referred to as a spoon denture and « ideal from the point of view of maintaining normal conditions for the gingival tissues but lacks firm retention. For this latter reason it is not advocated for young children and teenagers, in most cases, since it may be dislodged easily during robust activities. The T-shaped denture with inter- dental clasps is preferred for such patients {see fig 458(c))- CLINICAL DENTAL PROSTHETICS Fra. 458(f). -Line Diagram Illustrating the T-shaped Partial Denture. Class IV. Occlusal loading. Tissue-borne, except for the areas associated With the interdental clasps which become tooth-borne where the clasps cross the occlusal surface between 65(56 Antcro-postmor loading. Mosement is presented by the collets and clasps of 65(56. A labial flange is not so important in this design as it u in the case of a spoon denture. Vertical displacement. Direct retention from the interdental clasps and indirect retention of the anterior saddle b) extension of the palate of the denture posteriorly, thereby al«o pros irimg a more accessable area for tongue control. KENNEDY CLASS IV PARTIAL DENTURES FiO. 459(4)- 6i6 CLINICAL DENTAL PROSTHETICS Fic. 459 ( a and 5 ). -Meta! Anterior Saddle Partial Upper Denture Class IV. Thu denture was designed as a temporary measure to overcome the hyperplasia occurring in the rugae area palatal to the 32(23 resulting from recesses for spring attach- ments in the fitting surface of an orthodontic appliance. It is not considered a suitable design for a pennanent denture as too great a load would be placed upon the 2I2 which bear cingulum rests. After a period or approxi- mately two months the hyperplasia had resolved and a new denture was constructed of a conventional design. One important aspect to be considered when designing a partial demure for the replacement of one or more anterior teeth in the young person is stability of the denture against the pressure of tooth movement during jaw growth and tooth eruption. In the young person an anterior space may rapidly close when a natural tooth is lost. Even when a denture is fitted this tendency for the gap to close may continue and displace the denture palatal!) unless the denture is held firmly in the saddle region by clasp arms placed on the labial surface of the abutment teeth and the denture base carried onto the cingulum of these teeth so that the anterior saddle is virtually wedged between the abutment teeth (fig. a and 4 ). A labial flange is also considered to be of assistance in such cases A spoon denture is contra-indicated when any possibility exists of tooth drift. KENNEDY CLASS IV PARTIAL DENTURES 6 Fic. 45<)f0- - This figure shows four acrylic partial dentures which could be improved, either slightly or considerably, in design from the consideration of maintaining normal gingival conditions for the standing teeth Bottom lift: Kennedy Class I. A denture could be designed to clear the gingival margins of the at 1 134 provided that adequate support against lateral loading could be obtained from the saddles. Bottom right: Kennedy Class II. This design could be changed to allow clearance of the gingival margins of the 543). The 6I4 could be clasped to form a line of direct retention so that 3 j J and [67 act as renprocating indirect retainers Toh right: Kennedy Class III. The gingival margins of the 54I7 could be left uncovered and the palate extended posteriorly to provide for tongue control. If the 7J4 arc clasped there would be direct and indirect retention Tof> left : Kennedy Class IV. All gingival margins could be freed by a spoon denture in the adult person, or a large proportion of the gingival margins freed by the use of the T-shaped denture when greater retention b required. Chapter XXI 1 1. THE POSITION OF PARTIAL DENTURES IV RELATION TO THE TREATMENT OF THE MOUTH AS A WHOLE Treatment Planning In order to co-ordinate the treatment of a patient requiring a partial denture it is advisable to formulate a plan which may be used as a routine at the initial examination. Such a plan could be: 1. History • a) Previous partial denture experience, recorded as: li) Satisfactory fii) Unsatisfactory liii) None ( b ) What arc the patient’s reasons for requesting a demure? i i) For restoration of appearance (ii) For improvement in mastication fiii) Old denture now ill-fitting or broken. 2. Clinical Examination ia) Condition of remaining natural teeth: ii) Carious rii) Pcriodon tally involved ( b ) Condition of mucosa i c) Type of ridge in the edentulous areas d) Occlusion of the natural teeth t ) Articulation of the natural teeth f) Condition likely to cause instability 3. X-ray Examination jc) For caries undiscovered at the clinical examination (b) For evidence of the condition of the bone surrounding the natural teeth and that of the saddle areas. 4. Study Models fi) History . This information is extremely useful. A patient not wearing a denture, who really needs one, may have had 618 TREATMENT PLANNING 619 one previously but discarded it because it was painful, moved during mastication or was a general source of annoyance. An examination of such a denture, if available, may lead to the discover^' of a basic error of design or, by questioning the patient further, the discovery of some aspect of the design which the patient found irritating, thereby providing the operator with valuable information for consideration when designing the new denture. For example on the basis of this information the retention of the new denture may be increased to overcome movement during mastication and speech, or the position or shape of connectors may be changed to o\cr- come irritation to the tongue. (Figs. 460 and 461 show a case in which alteration of design led to improvement.) The reasons why a patient requests a denture may be due to his inability to chew food adequately or to the fact that lost anterior teeth have spoilt h is appearance and speech. Information on these points provides the operator with know- ledge of the aspect of the denture with which the patient is most 6c r <*) He. 460 (а) Upper skeleton design with encircling clasps and projection clasps - note the long amt projection clasp on the left side of the illustration. Patient complained of irritation from (t) numerous ‘wires,’ (a) food under the posterior palatal bar, (3) thick posterior palatal bar, (4) consciousness of anterior pabtal bar during speech (б) Lingual bar and projection clasps Patient complained of ‘worry’ from the projection clasps and a tendency to play with the lingual bar with the tip of hi) tongue. concerned and therefore the lines on which criticism • may develop when once the denture is fitted. Treatment and denture design can then be planned accordingly. ( 2 ) Clinical Examination The fitting of partial dentures should be the last stage in a scheme of treatment designed to render a person dentally fit. It may appear axiomatic and therefore unnecessary to stress that all extractions, fillings and gum treatment should be completed prior to the fitting of a partial denture. In addition, these fillings and extractions must be co-ordinated to a treat- ment plan and not performed as isolated operations. The con- TREATMENT PLANNING 621 sidcration of the necessity for a denture, therefore, should not be left to Ike end of the treatment but should be planned at the patient's frst lisil so that the mouth may be prepared suitably for the contemplated prosthesis. The initial examination must be a careful appraisal of all the remaining teeth. Carious teeth arc noted and a decision made regarding their conservation or extraction. It is most irritating having planned treatment, designed a partial den- ture, and discussed their case with the patient, to be faced with the extraction of a tooth at a later date and the possible need to re-design the denture. Those teeth which require con- servation may require a special type of restoration to fit in with the denture design, e.g. a gold inlay or a gold crown, and for this reason the conservation treatment and denture design must be co-ordinated. Details of the gingival condition are recorded so that this information is at hand during the study of the X-ray negatives. The mucosa is examined and any areas of inflammation 62! CLINICAL DENTAL PROSTHETICS Fic. 461 Lpper metal plate with minimum tfosp attachments. 61 Lower metal limpial plate *- no clasps Patient reported complete toleration of new denture* and had no complaint relating 10 inadequate retention or stability as a result of the reduction in immbrr or teeth clasped noted. Assessment of the health or otherwise of the mucous membrane is based largely on its colour and texture, and its attachment to the remaining natural teeth. It should be a uniform reddish-pink colour , a colour tcJjjch, though difficult to describe is easily recognised after one or two healthy mouths have been examined. Redness is a sign of reaction to irritation which may be either mechanical, chemical, bacterial or any combination of these, but whatever the cause it should receive attention before the tissue is covered by a denture. Although redness is the commonest change in colour to be noted!, whitish patches or spots arc frequently seen, and the cause of any variation from the normal colour must be diagnosed and, if necessary, treated. The texture is assessed by palpation and the ideal is an even TREATMENT PLANNING 623 thickness of firm mucosa neither very thin nor pendulous and flabby. The form of the edentulous ridge should be noted as hard and well shaped, knife edged or flat ( see Chapter II). This information when considered in conjunction with X-rav photographs will enable an assessment to be made of the load which the saddle areas may be expected to withstand and the denture design related to it. The depth of the sulci should also be noted. A clinical estimation of their depth is important since study models i see page 628) cast from impressions taken in stock trays may pro- duce an inaccurate picture of the true depth of the sulci due to over or under extension of the stock tray. This may result in an inaccurate design of the dentures on the study models the error only being discovered when the working models, cast from functionally trimmed impressions, are to hand. The natural dentition with the teeth in occlusion should also be observed as part of the examination and any teeth which are considerably over-erupted noted for possible extraction. In cases with close bites where the upper incisors have been lost the lower teeth may be in, or almost in contact with the palatal mucosa (fig. 462). Such cases may require periodic grinding of the lower incisors during visits for con- servation treatment to reduce the tooth height gradually so that a partial denture may be fitted later. This may consist of a very thin stainless steel or chrome cobalt plate to attach the anterior teeth to the denture if the lover incisors are not quite in contact with the mucosa of the palate. If they are in contact then the attachment of the teeth to the denture may have to be by a buccal bar approaching from the buccal side and not from the palate. In very severe cases the vertical dimensions may have to be increased by an ovei clay denftsxe w. order that a partial dmt'ite may he fitted at all (see fig. 463). The teeth should also be examined when articulating from centric to lateral occlusion. If good balance and tooth contact is maintained during these excursions the dentures should be set up to follow this pattern. This will require the use of an Fic. 462. - Patient with a very dose bite anteriorly nho has to have ill extracted. adjustable articulator and *a face-bow recording so that the artificial teeth may be set in balance with the natural teeth. In many instances however only a limited articulation occurs in lateral movements before posterior tooth contact is lost owing to the depth of the anterior over-bite which may cover half, or more, of the labial surface of the lower incisors: in such cases when the anterior teeth are brought into edge to edge contact the posterior teeth are completely out of occlusion. Dentures in these cases are unlikely to result in cuspal inter- ference posteriorly and can therefore be set-up using a plane- line articulator, any slight cuspal interference being reduced by the careful use of articulating paper and carborundum stones. Obviously such deep overbites cannot be eliminated by grinding the natural anterior teeth to bring the posterior teeth into contact without drastic loss of tooth substance, which in *hc authors’ opinion is not justified. "'Ytors likely Jo unstabilize a partial denture are noted so ne dcattff'&Spfcsign may be developed to overcome them. 624 CLINICAL DENTAL PROSTHETICS Fig. 462. - Patient with a very dose bile anteriorly who has to have ill extracted. adjustable articulator and a face-bow recording so that the artificial teeth may be set in balance with the natural teeth. In many instances however only a limited articulation occurs in lateral movements before posterior tooth contact is lost owing to the depth of the anterior over-bite which may cover hair, or more, of the labial surface of the lower incisors: in such cases when the anterior teeth are brought into edge to edge contact the posterior teeth are completely out of occlusion. Dentures in these cases are unlikely to result in cuspal inter- ference posteriorly and can therefore be set-up using a plane- line articulator, any slight cuspal interference being reduced by the careful use of articulating paper and carborundum stones. Obviously such deep overbites cannot be eliminated by grinding the natural anterior teeth to bring the posterior teeth into contact without drastic loss of tooth substance, winch in the authors’ opinion is not justified. Factors likely to unstabilize a partial denture are noted so that the denture design may be developed to overcome them. TREATMENT PLANNING 62 = Fig. 463 (a) Same paiienl as 462 after extractions. Note how 21(13 sink right into palatal mucosa making it quite impossible to fit a denture approaching from the palatal side. Such factors may be jaw relationship, variation in the relative size of the maxilla to the mandible and tongue size: fraenal attachments which are likely seriously to interfere with the peripheral outline may very occasionally require surgical treatment. (3) X-ray Examination Bite-wing films are desirable for the diagnosis of caries either interstitially or under existing fillings and full mouth X-rays may be required in order to estimate the extent of alveolar absorption associated with any existing periodontal lesions. The condition, and extent, of the bone surrounding the natural teeth will give an indication of the probable load to which a given tooth may be subjected without rapid deteriora- tion of its supporting structures. In a similar way the radio- graphic appearance of the bone structure in the saddle areas wall indicate the likelihood of changes occurring in the bone TREATMENT PLANNING 628 CLINICAL DENTAL PROSTHETICS when a masticator)’ load is applied through a denture, poorly formed bone showing signs of degeneration will obviously not withstand the same loading by a denture which would be tolerated by dense, well formed bone with a good trabecular pattern {see fig. 417). This information, coupled with that of the case history and clinical examination and used in conjunction with study models, gives the operator a sound basis on which to plan the denture design. (4) Study Models These arc plaster models of the mouth cast from hydrocolloid impressions and set in an articulator either by using the intcr- digitation of the teeth as a guide to centric occlusion, or by utilizing a wrax template record taken at the same time as the impressions. A wax template record is taken by placing a soften- ed roll of pink wax about as thick as a finger on the edentulous ridges and occlusal surfaces of the standing teeth of the mandible and requesting the patient to close the teeth firmly through the wax, care being taken to see that the teeth are in centric occlusion (fig. 464). It is left in this position for two or three minutes to harden and then removed and chilled. The proce- dure can be speeded up by syringing the wax with cold water whilst still in position in the mouth. Examination of Study Models The models should first of all be examined in occlusion and the following points observed. (a) Over-erupted teeth (fig. 327). The presence of such teeth may make the fitting of a partial denture difficult or impossible and consideration must be given cither to the extraction of the ofiending tooth or teeth if the over-eruption is gross, or the grinding of the occlusal surface if it is only slight. {b) The closeness of the bite (fig. 463(a)). In the incisor region the lower teeth not infrequently occlude either with the palatal mucosa or so close to it that not more than 1 mm. space exists. In such cases it must be decided whether the vertical height has closed and should be restored as part of the treatment {see Chapter XXVI) or whether a thin metal base or other technique should be used in the denture design. TREATMENT PLANNING 629 Fic. 4G4. (c) The closeness of the interdigitation of the teeth. If partial dentures are to be tooth-borne {sre page 470) rests will have to be fitted upon certain of the natural teeth. Such rests take up space and those teeth which arc to carry them frequently require either grinding or the fitting of inlap pre- pared in such a manner as to provide this space {str figs. 4G3 and 4G6). In addition part or the tooth which opposes the occlusal rest may have to be ground. The study models will Tie.. 463, -The dotted line* illustrate the type of Grinding frequently required before an occlusal rest can be etnpWvrd. 630 CLINICAL DENTAL PROSTHETICS show if space for rests exists or where tooth grinding will be required. The study models should then be examined separately and the dentures tentatively designed in pencil. As this is done the value of any isolated tooth may be assessed and a decision reached whether such a tooth will assist in the retention of the denture or make its construction less satisfactory and thus might be better extracted. Teeth which show exaggerated inclinations and which would make the insertion of a denture difficult, should at the same time also be noted and an estima- tion made regarding the value to be gained by retaining such a tooth. If there is no advantage in retaining the tooth then it should be extracted. The following case illustrates how study models are used (see figs. 467 and 468) . The points to be noted are : (a) The upper right first molar tooth considered by itself requires a simple occlusal filling, but when considered in occlusion with the lower model it is seen to be grossly over- erupted and will make the construction of a lower partial denture difficult. In addition the patient requires an upper denture because the upper left quadrant of the mouth is edentulous and to fit a partial denture to such a unilateral Tic. 467 (&V Lower model* ® 3 2 CLINICAL DENTAL PROSTHETICS Fig. 468. - Specimen study models seen from right side. case presents difficulties of retention which the pro\ision of an edentulous space in the upper right quadrant will simplify. Therefore, for two reasons it is better not to restore the upper right first molar but to extract it. ( b ) The lower right first premolar and second molar teeth require proximal fillings. The lower partial denture, however, requires to be tooth-borne on this side with occlusal rests seated on these teeth. On viewing the models in occlusion no room exists for such rests as the teeth arc closely interdigitating. Therefore, these teeth should be restored with inlays in which suitable seats for the occlusal rests would be prepared. (c) The lower left second premolar tooth is excessively inclined lingually and will make the fitting of a lower denture somewhat )lt. For mastication purposes the tooth is of ’■ V vah> * • and on balance it is better to extract TREATMENT PLANNING 633 Had study models not been taken, and had the case not been considered as a whole with the final fitting of partial dentures in mind, the upper right first molar might hat c been filled, the lower right first prcmolar and second molar filled to occlude with the upper teeth and the lower left second premolar left in place, and not until impressions had been taken and model provided for the construction of the dentures would the points tthich have just been discussed become painfully apparent. Chapter XXIV TAKING IMPRESSIONS OF THE PARTIALLY EDENTULOUS MOUTH AW the materials commonly used for impression tailing and their methods of preparation have been fully described in the section on full dentures. It is only intended therefore to describe here the essential points in their application to the taking of partial impressions. Trays for Partial Impressions - The type of tray required for an impression will vary in relation to the number of natural teeth standing. If the majority of natural teeth are standing a stock box tray may be used ( see figs. 469 and 470) and in some cases no second impression in a special tray will be required. If extensive edentulous spaces exist, a preliminary impression in a stock tray will be required PARTIAL IMPRESSION': 636 CLINICAL DENTAL PROSTHETICS Fig. 471. - Special tray for partially edentulous mouth cut away so as not to include unnecessary labial undercuts. sulci bounding the edentulous area to be taken. The tray is adapted by filling that part of it which will cover the edentulous area with softened composition and then inserting the tray; when the tray is in place the cheek is manipulated so as to trim the composition in the sulcus. The tray is then removed and the composition impression of the edentulous ridge widened and deepened slightly with the finger to allow room for the material to be used for the final impression (see fig. 472). The problem of producing an accurate model of a partially edentulous mouth is considerably greater than that of the wholly edentulous mouth, due to the fact that natural teeth are normally undercut and are composed of unyielding tissue. Many techniques have been evolved, employing many different materials, in attempts to gain accuracy but the present-day alginates have generally superseded such techniques as the plaster of Paris impression, sectional composition impression and the agar-agar hydrocolloid impression since the alginate impression is both accurate and easy to obtain, provided that the manufacturers’ instructions are followed strictly. PARTIAL IMPRESSIONS 637 Fio. 472. - A method of adapting a box tray w ilh composition. Impression Materials The Alginates To produce an accurate impression of the hard and soft tissues of the mouth it is necessary that this material be used in a rigid type or tray which will not be distorted during the working period, particularly the moment of withdrawal from the mouth when considerable force is often employed. This is extremely important when a model is required for the con- struction of a metal casting in which the slightest distortion in an impression becomes irritatingly obvious when the casting is tried-in in the mouth. For such an impression a rigid tray is essential, it may be either a special tray made of ‘cold cure’ acrylic or cast in tray alloy or a stock box tray adapted with composition. In the latter case it is desirable when taking an upper impression to post-dam the tray with soft wax and insert the tray so that this soft wax is first seated in close contact with the tissues; this will prevent the impression material escaping posteriorly, which is desirable both from 638 CLINICAL DENTAL PROSTHETICS the point of view of the comfort of the patient and also because a mass of alginate unsupported by the tray will tend to pull away from the palate and also distort the impression material farther forward. The ordinary compound special tray may be used satisfac- torily where extensive saddle areas are present, which require the denture periphery to be placed accurately at the functional level of the various sulci, since extensive saddles indicate only a few natural teeth standing which do not usually restrict the easy removal of such an impression and therefore there is little chance of distorting the impression trav. Alginate material should be placed in those areas of the mouth where it is anticipated that air may be trapped prior to the insertion of the filled tray. Such areas are the palate, the sulci lateral to the tuberosities, the sub-lingual pouch and in the case where a model is required for a casting which bears occlusal rests then a little impression material should be rubbed into the occlusal pits and fissures of the natural teeth to avoid the small bubbles which may otherwise occur in the impression and make the fit of the rest inaccurate. Only those areas of the mouth required for the construction of the denture should be included in the impression because alginate material distorts easily, and to take an impression of the entire jaw when only the replacement of a few teeth is intended is both undesirable and unnecessary. Sjnlkehc Rubber Base Impression Materials Two \arictics of synthetic rubber base impression materials ha\c become available in recent years: the Thiocol ‘rubbers’ and the Silicone ‘rubbers’. Thiocol is the patent name of a poh sulphide poUmcr which when mixed with lead peroxide polymerizes further into a semi-rigid ‘rubber’. The Silicone rubbers arc derived from the Siloxanc chain (basic unit Sio.) to which are attached methyl or phcml groups. This material can be polymerized to form a rubber by the addition of certain organic salts of heavy metals, c.g. dibutyl tin dilauratc together with tetraethyl pol> silicate*. » McLran.J. W. (1938) Dent. Pratt. PARTIAL IMPRESSION'S 639 For the purposes of making dental impression materials the polymerizable materials are mixed with such fillers as zinc oxide, chalk or starch to produce a thickish paste. In the ease of the thiocol rubbers, the accelerator is similarly mixed into a paste but with the silicones the accelerator is in the form of a liquid. Both materials when set form soft but adequately rigid rubbers which produce faithful impressions exhibiting excellent surface detail. The polymerization contraction for the tluocols as given by Jorgensen 1 vary from 0M3 per cent to 0^39 per cent; for the Silicones as given by Tomlin and Osborne 2 0-63 per cent to 0‘8o per cent after twenty-four hours. For a detailed explanation of the chemistry and properties of these” materials the reader is referred to the appropriate texts. Impmsion Taking with these Materials To take an impression of the partially edentulous mouth with either of these materials a close fitting special tray of cither acrylic or base-plate material is required. Although when mixed both these materials arc sticky they do tend to pull away from the tray when removing the impression from the mouth unless its fitting surface has been well roughened or some fibres of cotton-wool have been fixed to it with sticky wax. Some operators prefer to use perforated trays when employing the Silicone materials. Mixing the Materials A suitable length of the impression material is squeezed Horn the tube on to a glass or porcelain slab and in the ease of the Thiocol material an equal length of the accelerator is squeezed beside it: with Silicone materials the accelerator is added drop by drop according to the manufacturer's instruc- tions. The impression material and its accelerator are then thoroughly mixed with a broad spatula, loaded into the tray which is inserted into the mouth in the usual manner. The setting time of these impression materials varies from 1 J^rgciwtn. K. 1 ), (iqj6) Acta Odontoiogiea Scandtnarico, 14, 313. * Tomlin, H. R. and Osborne, J. (igjOI 105. 407. CLINICAL DENTAL PROSTHETICS 64O 4 to 8 minutes or more and depends on the make of the material and the amount of accelerator incorporated. All require to be held steady in the mouth for what appears to the operator and certainly to the patient to be an indefinitely long time. Removal of the impression from the mouth after the peri- pheral seal has been broken is simple -the completed impression exhibits a smooth, detailed surface (see fig. 473). In spue of claims by manufacturers that impression taken with either of these materials exhibit little or no dimensional change they should be cast soon after remo\"iI from the mouth if the highest degree of accuracy is required. The Use of these Materials They can be used for any impression but ha\ e little advantage over the alginates save in bulk, so Tor patients who exhibit a marked tendency to retching they can be employed although in these cases extra acceleration is necessary to shorten to a He. 473. - Completed impression taVen in a synthetic rubber material. PARTIAL IMPRESSIONS 6^1 minimum the time required for the impression to be held in the mouth. The type of case in which their value is greatest is with those patients who are unable to open the mouth fully and yet require a partial denture. In such cases alginate material will tear on the standing natural teeth when the impression is removed from the mouth whereas synthetic rubber will not. Composition and Alginate This technique is most commonly employed for obtaining study models. It can be used as a method for obtaining a final working impression, but it must be remembered that it usually produces an impression which is over-extended in the region of the sulci and therefore the peripheries of the denture must be designed accordingly. As large a tray as is convenient, without causing distortion, is filled with softened composition and an impression taken, but before the composition has time to harden, the tray is moved about from side to side and back- wards and forwards, thus the impression is finally only an approximate fit. On removal more distortion can be caused with a finger in any area where there is a severe undercut or around isolated teeth; the composition must then be thoroughly chilled in cold water and trimmed if necessary. This distorted impression is now used as a special tray and the impression taken with a wash of alginate: if the composition is dried and quickly flamed immediately before putting in the alginate there is no need to use sticky wax to keep the material in the tray. Composition Composition is, for all practical purposes, non-elastic, except for a short time during its cooling period, and it there- fore distorts during removal from the mouth and will not accurately reproduce an undercut unless a special sectional technique is employed. It is a valuable material, however, be- cause it is the only material which will compress the soft tissues. Sectional Impressions. — If it is desired to use composition for taking a detailed impression of a partially edentulous mouth the impression must be taken in sections, each one being CLINICAL DENTAL PROSTHETICS 642 removed in a direction which eliminates the undercut area. For example an accurate composition impression can be taken of a single tooth if the labia! surface together with part of the mesial and distal surfaces is taken and removed at right angles to the long axis of the tooth, thus: fig. 474. This first section is chilled, reinserted and the palatal or lingual portion taken in the same way but removed in the opposite direction, thus: fig. 475. Finally both these sections arc replaced and the third im- pression taken of the occlusal surface thus: fig. 476. Grooves should be cut in each section so that succeeding sections will key into place and the final collection can be sealed together with a hot knife before the model is poured. The same principles are used when taking an impression of many teeth for the construction of a partial denture and the number of sections which will be required and the direction of removal of each can be determined by the examination of a Fig. 474. - Impression of the buccal surface with part of the mesial and distal undercuts. The composition has been trimmed and pits cut for keying with the subsequent sections. Impression withdrawn buccaUy. PARTIAL IMPRESSIONS 645 study model. Each section should have a stiff backing cut from sheet metal to support the softened material and to allow some pressure to be applied in pressing it against the teeth or soft tissues. The composition should be handled in the same way as has been described for edentulous impressions, i.e. soften, insert, remove, chill, dr)', flame, temper, reinsert with pressure, remove and chill. A completed impression is shown in fig. 477. Plaster of Paris This material is rarely used today for taking impressions of the partially edentulous mouth because of the difficulty of technique. It is inserted soft into the mouth in a box tray and when set the tray is removed and the set plaster fractured into pieces which are then reassembled in the tray (see fig. 478 a and b). Although a highly accurate material small pieces tend to get lost or badly rubbed and this often invalidates the impression. Choice of Impression Material Although compression impressions should theoretically give the most satisfactory results and so should always be used, it is found that clinically they have little if any advanatgc over mucostatic impressions even in the case of tooth and tissue- borne dentures where the accurate distribution of masticatory pressures between the hard and the soft tissues is desirable. By mucostatic impression is meant one in which the soft tissues arc in no way compressed or distorted and therefore the impression material must flow readily and impose no pressure on the mucosa. Plaster of Paris is the only true mucostatic impression material though the hydrocolloids often give equally good clinical results. For tooth-borne or tissue-borne dentures, plaster of Paris is the most accurate. material, if it can be removed in a few large, easily reassembled, pieces but nowadays it has been almost entirely superseded by the alginate impression materials which have proved their accuracy over many years if the correct technique of their use is strictly adhered to. The great advantages of the alginate materials over plaster are that they are better liked and tolerated by the patient and as they do not 646 CLINICAL DENTAL PROSTHETICS PARTIAL IMPRESSIONS 647 fracture on removal, small pieces are not likely to be lost and invalidate the impression as may be the case with plaster. Where isolated teeth are missing, or where the natural teeth are spaced, an accurate plaster impression may be impossible, and a hydrocolloidal material will then be the material of choice. For tooth and tissue-borne dentures a sectional, composition impression with some degree of compression must be used if an attempt is being made to distribute the masticatory stresses between teeth and mucous membrane. Models Although satisfactory models for the construction of full dentures may be made from a mixture of plaster of Paris and artificial stone in equal parts, which has the advantage of being more easily cut and removed from acrylic dentures, only a hard non-expanding plaster or stone should be used for partial denture work, for two reasons: (1) All partial dentures have some contact with the natural teeth, as distinct from full dentures which are only in contact with soft mucous membrane, and as the teeth are rigid, or at least must be treated as such, the greatest possible accuracy is required. (2) A considerable amount of constructional work may have to be carried out on the model, such as the designing and fitting of clasps, and unless the model is hard, the resultant wear will naturally spoil the fit of the denture made on it. Chapter XXV RECORDING THE POSITION OF OCCLUSION IN PARTIALLY EDENTULOUS CASES In Cases with Many Natural Teeth Standing Frequently, sufficient natural teeth remain in both jaws to enable the position of centric occlusion to be accurately determined by their interdigitation when the models are occluded. If any doubt exists, however, as to the exact jaw relationship a squash record, as described for the study models, should be taken and the models articulated with its aid ( see fig. 464). In Cases with Large Edentulous Spaces In cases presenting extensive edentulous areas the models cannot be accurately articulated by the interdigitation of the natural teeth and it is necessary to record centric occlusion. Record blocks for partial cases are made in a manner identical with that employed for edentulous cases, the only difference being that the rims are not continuous but merely fill the edentulous spaces (see fig. 479). Sometimes it is only necessary to make a record block for one jaw if sufficient natural teeth exist in the opposing jaw. The relationship and interdigitation, if any, of the mandibular and maxillary teeth should be examined and noted before the record blocks are inserted in the mouth. In the majority of partial cases both the vertical and anteroposterior dimensions are indicated by the interdigitation of the remaining natural teeth. All that the operator is required to do, therefore, is to trim the occlusal surfaces of the rims until they just fail to occlude when the natural teeth are fully in occlusion. Localization grooves and pits are then cut in the rims as described in Chapter VI and a thin template of softened wax placed on the surface of the lower rim. The record blocks are inserted in the mouth and the patient requested to close the teeth together. The operator should watch carefully and G48 PARTIAL RECORDS 649 F«o. 479. - An example of a partial bite block. ensure that the natural teeth are fully in occlusion and inter- digitating correctly . The blocks are then removed from the mouth, the plaster models placed in them and the occlusion and interdigitation of the natural plaster teeth checked. The firm occlusion and interdigitation of the natural teeth is emphasized because a very common source of trouble with partial dentures is that when they arc finally fitted they are found to hold the occlusion open off the natural teeth by anything from 1 mm. to 4 mm. necessitating extensive grinding and mutilation of the occlusal surfaces of the artificial teeth ( set rig. 480). A contributor^' cause of this trouble is undoubtedly failure on the part of some technicians to pay sufficient attention to the elementary rules of flashing and packing thereby increasing the height of the denture in processing. The main cause of the trouble is usually traceable, however, to the fact that the plaster models were articulated with the natural teeth slightly out of occlusion. It sometimes happens that when the record blocks arc in the 650 CLINICAL DENTAL PROSTHETICS Fig. 4B0. - Natural term our ot occlusion » hen partial dentures arc in place, a bad but common fa jit. mouth with the jaws closed the natural teeth are observed to be fully in occlusion and yet when the blocks are removed from the mouth and the plaster models inserted in them the teeth are slightly separated. The cause of this trouble can be traced to the fact that the rims of the blocks were not trimmed so as to allow a small space to exist between the occlusal surfaces when the natural teeth were fully in occlusion and this has resulted in compression of the soft tissues by the record blocks and compression of the resilient wax rims of the blocks allowing the natural teeth to come into occlusion. When the record blocks are placed on the models, however, the plaster representing the soft tissues will not compress and consequently the natural teeth are held out of occlusion. Theoretically if partial dentures are set up and finished to a record obtained under such circumstances the dentures should compress the soft tissues when the jaws are closed and allow the natural teeth to occlude; in practice, however, this is not borne out and if this error of recording is made, considerable PARTIAL RECORDS 6$I grinding of the occlusal surfaces of the artificial teeth is always required; which points to the resilient nature of some dental waxes [see also page 653 el seg). Tooth-borne Dentures Where a metal casting has been constructed for a tooth- borne partial denture it is advisable to record centric occlusion with wax rims attached to the metal casting so that it is recorded under conditions similar to that occurring at the fitting stage of the denture. A word of warning is necessary however as it is easy to overlook incomplete occlusion of the natural teeth due to premature contact against an occlusal rest. In Cases Where the Natural Teeth Remaining in Both Jaws do not Occlude In these cases the vertical and anteroposterior occlusal relationships are assessed in the same way as described in Chapter VI. Such cases should be looked upon as edentulous with a few natural teeth standing and edentulous methods of record taking applied to them. Recording the Occlusal Relationship when Employing an Anatomical Articulator The stages are identical with those described for the edentulous case. If most of the natural teeth are standing the lateral records are taken by means of wax squash records otherwise blocks are used as described above. The essential difference between partial and edentulous cases is in the adjustment of the incisal guide table of the articulator. In partial cases the natural teeth provide the guidance and the table should be set so as to allow these teeth to remain in occlusion when lateral movements are made. Trial Dentures{try-ia) The main considerations at this stage are the verification of centric occlusion, the testing of the stability and retention of the denture and the approval of the appearance, by the patient, of any artificial teeth which are situated in the anterior part of the mouth. CLINICAL DENTAL PROSTHETICS occlt™ " ° r ' ! ' C T** *■*“ ,h ' — °,r !l,rc lhat ,hcir rc,ati ™ arc identical C-111'C II is possible lo occlude the models in a sliihlly in correct position uitli disastrous results. S I l,o, c cases requiring wax rcC o r d block to register tie pod- tio, IOC occlusion arc die ones in svhich clinical ernn erne opening and what happens is this: 1 lie record blocks arc trimmed down until the upper and losvcr blocks just occlude when the natural teeth arc in occlu- sion; soft wax is then interposed between the blocks and lie patient is instructed to close. What occurs then is one of two t tings, hither the dental surgeon fails to check accurately that t ic natural teeth arc in fullocrlusion-oftcn theantenor teeth are l -2mm.outofoccJusion and this frequently escapes notice being masked by a deep overbite when viewed from the front (ste % 4 o) - or otherwise the wn\ blocks compress tinder the force of occlusion and then elastically recoil when the teeth are parted, n either ease when the plaster models arc fitted into the record PARTIAL RI.CORD5 633 must be repeated until the denture slips into place. Under no circumstances should the denture be forced home because if this is done it will be found extremely difficult to remove. If the exact area of ban! contact cannot be discovered by observation a little lilaek carding wav may be run on to the surface of the denture fitting against the suspect tooth and the denture inserted as far as it will go. On removal the black carding wax will be found to have l>crn completely squeezed out of the area of hard contact which maj then be cased accurately. It is emphasized that easing a partial denture into place requires care and patience because if material is removed from the wrong area, or an excessive amount of material removed, the fit of the denture may be ruined. Such sarin* is unnecenary and is best avoided by a (artful and exact technique both at the chairstde and in the laboratory. Anjt'snxo tiif. Tins is carried out with articulating \ d wax templates as dcscriljcd for full dentures (see « a 1). Carr should always be takr; „ ensure that •* - \voii occlusal rests. - ,e r 6j 2 CLINICAL DENTAL PROSTHETICS The occlusion of the artificial and natural teeth is checked tnth celluloid strips for evenness of pressure, it being most important that the pressure is not heavier on the artificial teeth than it is on the natural teeth, the ideal being equal pressure on both. Clasps are assessed for their position and their relationship to the soft tissues - the gingival margins in the case of encircling clasps of tissue-borne dentures, and the sulcus and gum tissue in the case of projection clasps. The artificial teeth are observed for correctness of match of mould and shade, and any minor alterations of position and angulation of such teeth carried out at the chairside to produce maximum harmony with the natural teeth. Artificial anterior teeth of a tissue-borne trial denture should be left very slightly longer than the neighbouring natural anterior teeth in order to allow for the slight settling which occurs during the first few days after fitting or the finished denture and for any incisal grinding which is contemplated to produce a more natural appearance of the anterior teeth. Filling Partial Dentures If the model has been accurately surveyed and the denture and clasps properly designed (see Chapter XX) the denture should fit the mouth easily and accurately. It is frequently discovered, however, especially when acrylic resin is the base material, that the denture binds slightly on the natural teeth and will not go fully into place. If the surveying and blocking out of undercuts has been done carefully, the commonest cause of this trouble is that the plaster teeth on the model have been rubbed or chipped during the fabrication of the denture. In order to fit such a denture the acrylin resin round the teeth must be eased slightly and to do this accurately careful observation is necessary. The denture should be inserted in the mouth and very gently coaxed into place as far as it will go easily. Using a mouth mirror the whole area of the denture in contact with the natural teeth should be inspected and any point where the contact is hard noted. The denture is then removed from the mouth and a little of the acrylic resin in this area stoned away and the denture tried again and further careful observations made. This process PARTIAL RECORDS 653 must be repeated until the denture slips into place. Under no circumstances should the denture be forced home because if this is done it will be found extremely difficult to remove. If the exact area of hard contact cannot be discovered by observation a little black carding wax may be run on to the surface of the denture fitting against the suspect tooth and the denture inserted as far as it will go. On removal the black carding wax will be found to have been completely squeezed out of the area of hard contact which may then be eased accurately. It is emphasized that easing a partial denture into place requires care and patience because if material is removed from the wrong area, or an excessive amount of material removed, the fit of the denture may be ruined. Such easing is unnecessaiy and is best avoided by a careful and exact technique both at the chairside and in the laboratory. Adjusting the Occlusion This is carried out with articulating paper and wax templates as described for full dentures (see Chapter XJI). Care should always be taken to ensure that the occlusion is not heavy on occlusal rests. The Increased Vertical Dimension The development of an increased \ertical dimension is an ever present problem in partial denture prosthetics. The causes of this may be of clinical or technical origin and all too frequently the technician is blamed for such an occurrence resulting from failure of the dental surgeon to obtain the correct occlusion in the first place. CLINICAL DENTAL PROSTHETICS 654 check the occlusion of the models against the patient’s natural occlusion and to ensure that their relations are identical because it is possible to occlude the models in a slightly in- correct position with disastrous results. Those cases requiring wax record blocks to register the posi- tion of occlusion are the ones in which clinical errors cause opening and what happens is this: The record blocks are trimmed down until the upper and lower blocks just occlude when the natural teeth are in occlu- sion; soft wax is then interposed between the blocks and the patient is instructed to close. What occurs then is one of two things. Either the dental surgeon fails to check accurately that the natural teeth arc in full occlusion -often the anterior teeth are 1 - 2 mm. out of occlusion and this frequently escapes notice being masked by a deep overbite when viewed from the front (see fig. 480) - or otherwise the wax blocks compress under the force of occlusion and then elastically recoil when the teeth are parted. In either case when the plaster models are fitted into the record PARTIAL RECORDS 655 blocks prior to articulating them the plaster replicas of the natural teeth will be slightly out of occlusion and unless very careful comparison is made with the position of occlusion of the natural teeth the error will pass unnoticed [see figs. 480 and 481). Frequently this cause will escape notice at the try-in stage because again the wax of the set-up teeth will compress on occlusion. When the unyielding acrylic dentures are fitted, how- ever, the error will become obvious and a lot of time-consuming grinding will be resorted to or otherwise the patient will be instructed to wear the dentures for a few days in the hope that they will settle. If they do settle it will be at the expense of the gingival margins, and soft tissues. Actually the degree of so-called settlement of a properly constructed and designed partial denture is very’ small. Fro. 481.— A sagittal section through the plaster models of a partially edentulous case with record blocks in place: (e) Close contact of the upper and loner front teeth which copies accurately the occlusion of these teeth in the mouth. ( 4 ) Lack of occlusion of the front teeth due to recoil of the wax blocks, contact with the baseplate or careless articulation. Inaccurate occlusion such as this frequently escapes notice if viewed casually from the front in the direction of the arrow (compare with fig. 480). 656 CLINICAL DENTAL PROSTHETICS Technical Causes The first of these is a continuation of the fault already men- tioned, i.e. failure to occlude the plaster models so that the plaster teeth truly represent the occlusal relationship of the natural ones. If the fixing together of the models is left to the technician such things as wax recoil, excess of wax, warping of wax and rubbing of plaster teeth may all contribute to this error, and it is strongly advocated that the union of models by means of wire strips or sticks should be made at the chairside after the comparison with the natural occlusion has been made (set fig. 482). The second and very common technical fault is the gradual opening of the vertical dimension as the artificial teeth arc set up. Frequently in partial cases the vertical or inter-alveolar space for a tooth is limited. The tooth is ground, but not sufficiently, the articulator is closed forcefully and the opponent plaster tooth nibbed and the vertical dimension thus opened Fig. 482. — Method of uniting models with tnatchslkks (or wire) and sticky was, <0 as to ensure that they are correctly articulated bv the technician. PARTIAL RECORDS 657 slightly. The posterior teeth are usually the chief offenders in this matter and if such a case is observed critically it will be seen that the anterior teeth arc often 1/16 in. out of occlusion, but that this is frequently masked by the overbite on the model if viewed casually from the front. When such a set-up is tried-in, the elasticity of the wax and the normally slack fit of the trial bases often allow these errors to pass unnoticed and they only become apparent when the unyielding finished denture is fitted. The swaging of thin tin foil over plaster natural teeth wilt prevent the rubbing of the surface when much fitting of an- opposing artificial tooth has to be carried out and the meticu- lous observance of the position of occlusion of the natural teeth all through the setting-up will prevent this occurrence. Processing 1 Finally the cause which is frequently the only one under- stood and blamed for an increase of vertical dimension in partial cases, i.e. that occurring during processing. The causes of this arc twofold: (a) Failure of the two halves of the flask to meet due to the extyusion of acrylic flash and thus an increase in the vertical dimension by the amount of this failure. **(6) The artificial teeth arc driven into the plaster containing them either as a result of excessive pressure applied through the acrylic resin or due to softness of the plaster or due to weakness of lack of support of the plaster. Two methods of flashing arc possible for partial dentures. In the first method the model and artificial teeth arc invested in one half of the flask and plaster caps built over the occlusal surfaces of the teeth to support and position them during the boiling-out of the wax and the packing and curing of the acrylic. The plaster in the second half of the flask merely acts as a ram to force the soft acrylic into the space which was occupied by the wax. This method will be referred to as packing through. • In the second method the case is flashed so that after boiling out the wax' and separating the two halves rif the flask the model is in one half and the teeth in the other. This method will be referred to as reverse packing. j ‘The jubilance of this first appeared in an article by one of us in the D.D.J., <1056)101,411. 658 CLINICAL DENTAL PROSTHETICS A cinematograph study through a Perspex window let into the side of a flask has given much information on this irritating phenomenon of the alteration of tooth position during packing in both these methods of flasking. Fig. 483 illustrates the flask with the Perspex window. The investing plaster, the model, a tooth and the supporting wax can be seen in cross section. In these studies a saddle consisting of four molar teeth set up in the normal manner has been used, the first tooth abutting against the window. The thickness of the plaster caps and the distance between the teeth and the model and the time and rate of closure of the flask being varied with each experiment. Fig. 484 shows frame enlargements from a Kodachromc cine film showing how the alteration in tooth position occurs in a case packed by the method of packing through. In the first frame the supporting plaster cap (a, fig. 48 \c) is seen intact supporting the tooth. In the second and subsequent frames as the acrylic (b) flow's between the model (c) and the tooth (n) F10. 483. -Flask with Perspex window; model and wax supporting teeth arc coloured to aid photography. PARTIAL RECORDS 659 I'lG. 484. (a) frame enlargements from a Kodachrome cine film ffltinming Jbe fsaciurr of a plasjcr op. Note how the first sign of a crack appears in frame 3(a) and then the cap rises in successive frames producing a space abov e the buccal cusp of the tooth. ( 4 ) The first 3 frames arc retouched ones from (a) showing wtiat happens in greater detail. The 4th frame is from further on in the film showing that the buccal cusp of the tooth has risen into the space. (c) Key to frames: set text. 660 CLINICAL DENTAL PROSTHETICS under the influence of the plaster wedge (e) of the second half of the flask a crack (c) is just discernible occurring in the middle of the plaster cap, and a space (h) has developed between the buccal cusp of the tooth and the plaster cap. In succeeding frames the space (h) gradually increases and the crack (c) widens and deepens. In fig. 484(6), frame 4, which is a continuation of the film some seconds later, the plaster cap is seen to be completely fractured and malpositioned and in the film when projected the tooth can be seen to rise into the space which has developed above it. From evidence provided by many cinematographic studies of this type of flashing the way to prevent such an occurrence is: (1) Use deep, well-supported caps, and place the model at the botton of the flask. (a) Pack the acrylic at the correct dough stage. (3) Close the flask slowly. (4) Refrain from adding extra acrylic and performing a second closure. Fig. 485 illustrates a single retouched frame from a cine film Fig. 485. —The black line on the plane of which the cusps of the tooth were situated before the was was boiled out runs slantingly across the top thin! of each frame. Note the craclu in the plaster radiating up from the cusps and the fact that the latter are above the black line now that the acrylic has been packed (the middle frame has been retouched to illustrate the details more clearly). PARTIAL RECORDS 66 1 taken through the Perspex window of a flask prepared for examining what occurs when the reverse method of packing is employed. A thin black line is scribed across the Perspex win- dow so that it lies on the plane of the extreme tips of the cusps before opening the flask after investment. The wax is then boiled out and the acrylic dough packed and closure of the flask carried out. At first the dough flows easily but when the flask is almost closed and the flash thin the pressure inside the flask obviously increases; suddenly cracks develop in the plaster supporting the tooth and the tooth is driven slightly into the plaster. Fig. 485 shows the cracks in the supporting plaster of the reverse half of the flask and the fact that the cusps now lie above the black line indicate that the vertical dimension has been increased. Several trials were filmed using the method of reverse packing in which a space is made for the inevitable flash by painting the plaster surface of the first half of the flasked case with a thin film of wax before pouring the reverse half, thus proriding a space for the flash. In each case the flow' of acrylic continued until complete closure of the flask was obtained and no pressure built up inside and no cracking of the plaster was visible. The cusps of the teeth returned at Full closure of the flask to their correct relationship with the black line. This method in practice gives consistently good results in partial cases with little or no increase in the vertical dimension of the denture due to processing faults and this technique is strongly advocated as a means of prevention of bite opening during processing. Chatter XXVI IMMEDIATE DENTURES Tlic term immediate denture is used to describe a denture which is entirely constructed Irefore the extraction of the teeth which it replaces and it inserted immediately after the extraction of the teeth. This term is med in preference to that of temporary denture which, though often employed, ii an unfortunate title for two reasons: (t) It ii used not only for dentures which arc made Ireforc extractions, hut a!«> for denture* made at any lime during the two or three months immediately following. (2) The idea is comcscd to the patient that the denture i« temporary when sshat is meant is that its usefulness is temporary, owing to the rapid change in shajv of the ah tolar ridges during the first few- months following extraction. Many techniques have Ixrn slrserilKtl fir constructing immediate dentures, most of them differing only slightly in detail, ansi in general they ran hr disided into two grtmps: (1) Without nhrolectomy. (2) With nl\ colectomy IMMEDIATE DENTURES 663 CLINICAL DENTAL PROSTHETICS Fio. 487. - Illustrating how the occlusal relationship of the jaws is indicated by the occlusion of 33|3- FlC. 488. — Upper and lower partial dentures have been fitted. 666 CLINICAL DENTAL PROSTHETICS Fio. 401. - The natural lower front teeth have been extracted and the lower denture to which the artificial front teeth hat e been added is being inserted. Note labial flange. need be retained for immediate replacement. If, however, as frequently occurs in cases presenting a large overjet, the front teeth do not make contact in the centric occlusion, then the upper and lower first prcmolarson cither side must be retained for immediate replacement. Once it has been decided which teeth arc to be retained, the posterior teeth are extracted. This is conveniently done by removing at one visit the upper and lower back teeth on the side which is not habitually used for chewing, and then a fortnight later extracting those on the other side. Sharp interdental bone is removed with rongeurs at the time of extraction. After the posterior teeth have been extracted the patient should be dismissed for the period of immediate healing and most rapid alveolar absorption. The longer this waiting period, up to six months, the better, for two reasons: (i) The more rounded will be the sharp edges of the tooth sockets and consequently the more comfortable will be the dentures, even under the pressure of mastication. 668 CLINICAL DENTAL PROSTHETICS (2) The period of rapid absorption will be over and thus the useful life of the dentures will be increased. In cases where most of the posterior teeth have been lost for some years, the waiting period after the extraction of the remainder need not be long; the already edentulous areas can be made to take the majority of the masticator)- pressure by suitably relieving the denture over the areas of recent extraction. When the healing period has elapsed, the patient is recalled for the immediate prosthesis. This begins with the taking of the primary impressions, usually carried out in composition or a hydrocolloid, in a stock tray ( see Chapter XXIV on impres- sions for partial dentures) from which special trays arc construc- ted and the working impressions secured in a hydrocolloid. The records are taken in the usual manner for partially eden- tulous cases. An anatomical setting of the teeth is not generally possible since the majority of people exhibit a rather deep overbite. Anatomically articulated dentures can be made when replacements become necessary due to alveolar absorp- tion. The models are articulated and partial dentures set up to replace the missing teeth and these are tried-in in the normal manner in the waxed-up stage. At this stage the anterior artificial teeth are selected and matched with the natural teeth. If the patient requires the shape, colour and surface characteristics or his teeth to be copied exactly, an additional hydrocolloid impression of the anterior teeth must be taken into which is poured molten wax to a level just above the gingival margins. The wax is thoroughly chilled in cold water and removed from the impression, after which the teeth are separated and reproduced individually in acrylic resin. If the try-in is satisfactory, the partial dentures are finished and fitted and necessary adjustments made until the patient is comfortable and the operator satisfied. The patient is dis- missed for a period of a few' weeks to become accustomed to the new dentures after which the immediate additions of the re- maining teeth are carried out as follows. An impression is taken of the remaining natural teeth and the model cast from it is kept as a record of the position and relationship of these teeth. This model is useful for reference IMMEDIATE DENTURES 669 -when setting up the artificial teeth even if an exact duplica- tion is not desired. Hydrocolloid impressions are taken with the dentures in position. When the impressions are removed from the mouth the dentures usually come away with them but if this is not the case the dentures must be accurately re-positioned in the impressions before casting. The resulting models are mounted on an articulator by means of a wax wafer or squash record. The Replacement of the Natural Teeth by Artificial Teeth The Upper Denture The plaster teeth are cut from the model and replaced by the artificial teeth. This is best achieved by removing and replacing one tooth at a time so that the form of the arch and the position of each individual tooth can more easily be copied if desired. Root sockets are prepared in the plaster model into which the necks of the artificial teeth are fitted so that when the completed denture is inserted in the mouth after the extraction of the natural teeth, the necks of the artificial teeth just enter the natural sockets (see figs. 493(a) and 494). The advantages of root socketing are: (1) It allows for the initial alveolar absorption. No un- pleasant gap appears between the neck of the tooth and the alveolar ridge since, as absorption takes place, more and more artificial root becomes exposed and the denture maintains the appearance of fitting to the gum. (2) It provides an anterior seal. It is equivalent to an exaggerated damming and materially assists in the reten- tion of the denture. (3) It provides resistance to movement. If during mastication there is a tendency for the denture to be moved on the ridges, root socketing will aid in resisting this movement. (4) It produces a natural appearance of the teeth growing from the gums. Three important points should be remembered when pre- paring the sockets in the model: (1) The direction of the socket should follow the long axis of the tooth. 670 CLINICAL DENTAL PROSTHETICS the absorbed alveolar ridge reasonably well three months alter the extractions. ( 4 ) The type of jocketing which leads to bone destruction. Note how the artificial root protrudes above the level of the absorbed alveolar ridge. Compare with fig. 495(e). (2) Never socket to a greater depth than 5 mm. (3) Do not carry the socket too far towards the palatal side: the socket should slope from the palatal gingival margin upwards towards the labial aspect. The reasons for the above statements are: (1) If the long axis of the root is not followed when preparing the socket in the plaster model the finished artificial root will be out of alignment with the natural socket and the acrylic root will impinge on bone preventing the denture from being seated accurately. Also the pressure exerted on the bone will cause pain and discomfort to the patient. (2) IF the artificial root is carried too far into the natural socket and also allowed to extend too far up its palatal aspect nc. 4 t ic sockets receiving the artificial roots. Unfortunately this protrusion of the upper teeth is not confined to the incisors but a so in\o \cs the canines and even if the teeth arc brought back 0 a more acceptable arch the prominent premaxilla and Fig. 500. - A case of superior protrusion. Twenty -four hours after the ah colectomy. The upper denture has been removed to show the alveolar ndtre. IMMEDIATE DENTUI Fig. 501. - A case of superior protrusion. Twcnt>-four hours after the alveolertomy. Note hosv the upper front teeth now pass behind the lower lip (compare with fig. 459). 68a CLINICAL DENTAL PROSTHETICS He. 502. - Illustrating the method of angulating the artificial root to the crow n of the tooth in order to correct, without performing an alveolectomy, the appearance of superior protrusion. canine eminences still continue to hold the upper lip forward presenting an unpleasant appearance. Such cases call for an al\ colectomy at the time of extraction in order to reduce the alveolar process and allow the lip to fall back when the teeth have been set farther palatally. The extractions and alveolec- tomy can be followed by the insertion of an immediate denture as mil be described in due course. (2) To Provide Better Retention and Stability: In cases where the factors of retention are adverse, such as the V-shapcd palate, poor posterior ridge formation, shallow sulci and a narrow upper jaw with a wide lower jaw, it is often advisable to produce an upper immediate denture having a labial flange. This flange increases the peripheral seal and resists lateral and antero-posterior movement of the denture. IVhen a labial flange is added in such cases, it is usual to perform a slight alveolectomy at the time of the extractions in order to form a smooth and rounded denture-bearing surface. Unless this is done there will often be insufficient room for the flange without obviously distorting the lip; also pressure of the flange on the sharp edges of the sockets and the interdental bone will cause considerable discomfort to the patient. (3) -'1 I r «7 Close Bite Anteriorly: Some patients exhibit a very deep overbite; the incisal IMMEDIATE DENTURES 683 edges of the upper teeth touching the gingival margins of the lowers and the lower teeth occluding with the soft tissues of the palate. Upper and lower alveolectomies are needed in these cases if sufficient interalveolar space is to be obtained to produce satisfactory* dentures, although some help may be obtained by slightly increasing the vertical height providing it is within the range of the freeway space. Close bites are not always quite so extreme and often sufficient space can be gained by removing bone from one jaw only. (4) The Preference of the Operator: It is not intended to enter into the controversy regarding the superiority of the socketed over the flanged type of immediate denture or vice versa; it is sufficient to note that some operators have very' strong views on the subject whilst the Authors consider that each technique has its place. In cases where only a slight alveolectomy is contemplated partial 'dentures may be constructed and worn by the patient as has already been described. In cases invoking an extenshe alveolectomy it is preferable to continue the immediate replacements from the try-in stage of the partial dentures since the reduction of the arch anteriorly may require the posterior teeth to be moved farther back and this can easily be done whilst the teeth are still mounted in wax. The trial partial dentures are used in the normal way to check the accuracy of the occlusal registration. Model Trimming The incisors and canine teeth on one side are cut from the model and the plaster representing the alveolar ridge is trimmed to the desired shape. This trimming will be from either the labial surface or from the alveolar crest, or both, depending on whether more labial space is required, as in a case with a prominent prcmaxflla or one presenting severely undercut areas, or whether more interalveolar space is needed, as in close-bite cases. Haring completed the trimming of one side of the model the opposite side is treated in the same way and any' final adjustments made until the 684 CLINICAL DENTAL PROSTHETICS anterior plaster ridge is shaped to correspond as nearly as possible to the condition which will be obtained after the extraction of the teeth and the associated alveolcctomy. A duplicate is now made of this trimmed model and on it a thin template (one thickness of wax) is produced in clear acrylic. This template is for the assistance of the surgeon and should cover as much of the denture-bearing surface as possible, for greater accuracy. The artificial teeth are mounted on the original trimmed model with such variations of the original positions of the natural teeth as may be desired. The set-up is completed with a normal labial gum flange and the denture processed and finished ready for insertion in the mouth. The surgical operation consists of extracting the teeth and trimming the alveolar ridge to the same extent as the plaster model. In order to ensure this similarity of shape the clear acrylic template is tried in the mouth from time to time during the operation, bone being trimmed away as necessary till it fits snugly without any rocking. In theory it is possible to see through the acrylic template areas where the gum is blanched indicating pressure on high spots: in fact this is often impossible owing to the presence of blood and the surgeon is dependent on his sense of touch. There are two points which merit emphasis as they are essential to the success of this operation. (1) Do not encroach on the area covered by the periphery of the denture. This region should not have been touched on the plaster model and accuracy of fit round the periphery is needed for retention. (2) Remove sufficient bone. If the denture presses on any high spots of trimmed bone it will be too painful to be tolerated and the denture will have to be left out until some absorption has taken place, or a new denture will have to be made. In cither case the advantages of an immediate denture arc lost. The removal of slightly too much bone, in the upper, is immaterial since the palate and periphery are intact and in any case the exactness of fit over the site of the operation is rapidly lost owing to alveolar absorption. IMMEDIATE DENTURES 685 This technique applies to both the upper and lower immediate dentures and the patient should be instructed to wear them night and day during the first week, only removing them for cleansing after meals. If the dentures are left out of the mouth for long periods during this first week some difficulty may be experienced in replacing them owing to slight swelling of the oral tissues. In time the dentures xvill become loose and will require re-lining or replacing; this can only be judged by clinical observation but if the peripheries have not been interfered with it is unlikely to occur in under six months. Immediate Dentures Without Prior Extraction of the Posterior Teeth In some cases it is necessary to fit immediate dentures without the prior extraction of the posterior teeth, e.g. when the anterior teeth are causing pain or arc excessively loose, or if the patient wishes to shorten the number of visits for extractions. This method is not suitable for general practice and should only be employed if the patient can be treated in a hospital or nursing home. The technique is briefly as follow's: fi) Impressions are taken in hydrocolloid of both jaws, care being taken to secure a good reproduction of the sulci. Such impressions are best taken in box trays whose peripheries have been built up with composition and functionally adapted. (2) The models cast from these impressions are mounted on an articulator by means of a wax wafer or squash record. (3) Duplicates of these models are made for reference when setting the teeth. {4) The teeth are removed from the model and the ridge trimmed as described for immediate dentures with alveolectomy; duplicates of these models are made and on them clear acrylic templates prepared. (5) The artificial teeth are set up and the dentures cured and completed with normal flanges. 686 CLINICAL DENTAL PROSTHETICS (6) The patient is admitted to hospital, the teeth removed and the ridges trimmed with the aid of the templates, and the dentures inserted. This technique gives remarkably successful results, its main drawback being that the rapid absorption renders the dentures an ill fit after a few weeks, and two re-linings are usually necessary within the first three months. Partial Immediate Dentures The socketing technique can be applied to any of the sixteen anterior teeth which are being replaced by a partial denture, and due to the stability of the partial denture, which has natural teeth to support it, the results are very satisfactory. Copying the Appearance of Immediate Dentures when Fitting the Replacement Dentures It is quite easy to copy irregularities of an individual’s anterior teeth when fitting an immediate denture because the artificial teeth can be placed in exactly the same positions and gi\cn the same angulation as the natural teeth. Wien the time comes to construct another set of dentures to replace the immediate ones, however, it is sometimes extremely difficult to copy the position and set of the teeth and many a patient who has been delighted with the appearance of the immediate dentures is very disappointed with the final set. A simple way to ensure an exact copy of the positions of the anterior socketed teeth of an immediate upper denture is to insert the denture and then mould a piece of composition over the labial surfaces of the ridge and the six anterior teeth. The composition is chilled in situ and then removed and excess composition trimmed away. It is then slightly softened and replaced in the mouth and given a final moulding followed by a second chilling. This piece of composition will fit the labial surface of the upper model and the artificial anterior teeth of the replacement denture can be placed in the impressions left by the teeth of the immediate denture and then waxed to the base plate (see fig. 503). When all the teeth arc in position the composition is removed and the labial flange waxed up. 688 CLINICAL DENTAL PROSTHETICS The Advantages of Immediate Dentures (1) The patient is never without anterior teeth. (2) There is little or no disturbance of the temporo- mandibular joint. (3) Masticatory function is maintained. (4) There is the minimum interference with speech. (5) The vertical dimension and the position of centric occlusion can be easily and accurately reproduced. (6) The facial contour is maintained. (7) Changes in the shape of the tongue are prevented. (8) No unnatural habits of mastication and speech will have been formed. (9) The position, shape, size and colour of the natural teeth can be reproduced with accuracy. (10) The sockets are protected during the healing period. The Disadvantages of Immediate Dentures (1) The occlusion of the natural teeth may be a bite of con- venience due to the movement of the teeth in those mouths where some of the teeth have been lost in earlier years. (2) Naturally deep o\erbites if reproduced in immediate dentures would produce prosthetic malocclusion. {3) The patient’s general health may not permit multiple extractions. (4) Additional expense for the patient. The first two disadvantages mentioned are not direct contra-indications for immediate dentures which could quite satisfactorily be constructed if the necessary alterations were made to the occlusion. They are valid contra-indications ft> the exact reproduction of the positions of the natural teeth. Chapter XXVII OVERLAY OR ONLAY DENTURES An overlay or onlay denture is one which is designed to alter the shape and height of the occlusal surfaces of the teeth over which it fits. Overlay dentures may form part of a conventional partial denture, or be fitted in a mouth in which no teeth are missing. They may be constructed of acrylic resin, gold or chrome cobalt (see fig. 504(a), (6), (r)). Conditions Requiring an Overlay Denture Overlay dentures are fitted to correct faults of occlusion and articulation, and four broad classes of such faults may be identified. CLINICAL DENTAL PROSTHETICS Ftc. 505. —A ease of abnormal occlusion resulting in trauma to gingiva! margins: (a) From the front. (b) From lingual side. (t) From the side. (a) Those causing damage to the tissues. Fig. 505 illustrates a case in which the occlusion is such that the upper incisors are biting into the labial gingivae of the lower incisors, and the lower incisors are traumatizing the palatal mucosa. Fig. 506 illustrates how the fitting of an overlay on the occlusal surfaces of the upper teeth lifts the incisive edges of these teeth from the tissues and prevents the damage continuing. ( b ) Those cases in which the occlusion is such that the lower teeth occlude palatally to the uppers ( see fig. 507). Such a condition makes it difficult or impossible for the individual to chew. The fitment of an overlay to the upper teeth shaped in such a manner that it occludes with the lower teeth enables the individual to masticate. (c) Those cases in which the occlusion is locked in the position of centric occlusion and attempts to make lateral chewing movements cause excessive loads to be imposed on the 6g2 CLINICAL DENTAL PROSTHETICS M Fig. 506. -Treatment of case shown in fig. 505 by fitting over fay. (a) Not? holes worn in it by use. {b) Fitting over upper teeth. (r) Compare with 505(a) to see how ailia have been raised from lower gingivae. 694 CLINICAL DENTAL PROSTHETICS OVERLAY OR ONLAY DENTURES 695 periodontal membranes of the teeth with consequent damage to these tissues. A traumatic occlusion of this type can frequently be corrected by fitting an overlay to the upper teeth thus providing a change in the cuspal relationships which allows lateral movements to be made (see fig. 508). ( d) Those cases in which pain or derangement of function of the tcmporo-mandibular joint results, or is considered to result, from faults of occlusion. This subject of occlusal dis- harmony and tcmporo-mandibular arthrosis has become prominent in recent years, and as it is far too extensive to be dealt with in a text on clinical dental prosthetics, the salient points only of the rationale of treatment of this condition by overlays is summarized below. For more extensive information on this subject the student is referred to the appropriate texts. The present day conception of the articulation of the mandible with the skull is that it is a triple and not a double Fig. 508. (a) A locked occlusion. (i) The overlay in place (r) The occlusion h now freel> sliding. 696 CLINICAL DENTAL PROSTHETICS OVERLAY OR ONLAY DENTURES 697 articulation. The mandible articulates with the skull through the two tcmporo-mandibular joints and also through the occlusal surfaces of all the teeth. For efficient and comfortable function therefore these three articulations must be in harmony. In addition the muscles controlling the mandible de\clop a pattern of movement which also harmonizes with the move- ment of these three surfaces. If one of these articulations fails to fit in functionally with the others then a condition of stress will develop which may produce symptoms of disfunction and pain. So far as the treatment of these conditions is related to overlavs, we are concerned here only with the disharmony of the occlusion and articulation of the teeth in relation to the other articulations. The position of the mandible when the teeth are in contact is determined by the interdigitation of the cusps which act as inclined planes and which under the influence of the powerful muscles of mastication seat the mandible in a definite relationship to the skull on each closure. CLINICAL DENTAL PROSTHETICS 698 If this position of the mandible is seriously out of harmony with the normal positions which the tcmporo-mandibular joints and muscles assume, then the joints and muscles will be forced to take up strained positions, and dysfunction of cither or both may supervene. The commonest example of this condition occurs when one or both condyles are forced to retmdc further into the glenoid fossae than the normal laxity of the joint structures will allow. Such a condition may develop as a result of the loss of the support of the posterior teeth as illustrated (fig. 509). In figure 509(A) the relationship of the articulating surfaces is illustrated before any teeth were lost. The premolars and first molars are then extracted and as a result of the extra stress induced in them and their lack of support, the last molar teeth tilt. This results in the lower incisors sliding upwards and backwards Fie. 509(4) - I45C hate been extracted and bate tillrd. The palatal turfaeet of the upper front teeth hate acted at an inclined plane up which the lower front teeth are drawn at the teeth occlude, forcing the mandible baefcwanb Note the relationship of the condole to the glenoid C**a and compare with («'. OVERLAY OR ONLAY DENTURES 699 along the inclined palatal surfaces of the upper incisors each time the teeth are occluded. This means that part of the power of the muscles of mastication is directed to driving the mandible, and consequently the condyles, upwards and backwards, and therefore on closure the mandible assumes a more rctrudcd position than the temporo-mandibular joints can accommodate. In a majority of cases this condition never develops because the attachments of the upper and lower incisors alter under the extra load applied to them, allowing the upper incisors to tilt forwards and the lowers lingually. If the pressure of the muscles of the lips and tongue is great or the attachments of these teeth is extremely firm however such tilting may not occur, and it is in these cases that symptoms of temporo- mandibular joint derangement or muscular strain may develop. The insertion of a partial denture with an overlay in such cases is aimed at restoring the occlusal relationship of the mandible with the maxilla to the original position, and allowing the condyles to assume their normal relationship to the glenoid fossae. A similar condition of disharmony can develop without the prior extraction of teeth as illustrated in fig. 510. In fig. 510(a) is illustrated the relationship of the condyles to the glenoid fossae when the mandible is in the relaxed position. From this position to closure of teeth in the position of centric occlusion, a pure hinge movement of the condyles takes place, and when this happens in the type of case illustrated the teeth do not inter- digitate (see fig. 510(11)). When the power of the muscles is increased the inclined planes of the teeth act as wedges, and the lower cusps slide up the upper cusps forcing the mandible to assume a retruded position, and driving the heads of the con- dyles backwards in the glenoid fossae. As described in the previous example, the teeth usually adjust their positions, by moving, to fit into the joint and muscle posi- tion of the mandible, but in some instances the power of the muscles surrounding the teeth is so great or their attachment to the jaw so rigid that no adjustment is made. It is in these cases that the reshaping of the occlusal surfaces by means of an overlay to fit into the temporo-mandibular joint and muscle position of 700 CLINICAL DENTAL PROSTHETICS 1'ic. 510 (a) A cue vsilli an atmomial occlmion the mandible in the relaxed position. Note «he relationship of the head of the conds le Jo the glenoid fossa i« normal li) An enlarged \ icwof the relationship of tlie Jrelli on initial contact. A« tlie muscle* apply power the lower teeth and the mandible wjJJ hr drawn in lhr cljrrrlion of the arrow* guided b\ the incline of the cu'jw and the head of the condole will lake up the relationship to the glenoid fossa shown in (c) when the teeth are fulls interdigitatrd. OVERLAY OR ONLAY DENTURES 701 the mandible is of value. Fig. 51 1 shows how this is effected. Although the above explanation sounds simple and convincing, it leaves a lot unexplained in relation to cases presenting temporo-mnndibular joint and muscle symptoms, many of which appear to have no simple explanation. Such symptoms are becoming increasingly common among young people in the age group of 17 to 23 years, especially females. Many of these cases would appear to be the result of general tension which has centred itself in the masticatory' muscles, especially the masse ters, and overlay dentures should nc\ er be prescribed for cases of temporo-mandibular joint arthrosis unless definite evidence of occlusal disharmony can be demonstrated. The method of assessing the presence of occlusal disharmony is by means of an occlusal analysis. This is carried out in identically the same manner as a check record for full dentures ( set Chapter XIII) with the difference that models of the patient’s natural dentition arc used instead of the artificial dentures. CLINICAL DENTAL PROSTHETICS /OO in the relaxed position. Note the rrlationdnp of die head of die Condi ft to the (denot'd f<««a ii normal. (4) An enlarged \ tew of the relationship of die irrlfi on initial ronlacl. A' tlic muscle* appU power the lower teeth and die mandible will be drawn in die direction of dir arrow* guided b> die incline of the cusjn and die tread of rtie roods le Mill tale op the relationship to die denotil Uo ilrnvn in {<) when tlie treth are fulls intrrdnjuatrd. OVERLAY OR ONLAY DENTURES 701 the mandible is of value. Fig. 51 1 shows how this is effected. Although the abo\e explanation sounds simple and convincing, it leases a lot unexplained in relation to cases presenting tcmpoiD-mandibular joint and muscle symptoms, many of which appear to have no simple explanation. Such symptoms ate becoming increasingly common among young people in the age group of 17 to 25 years, especially females. Many of these cases would appear to be the result of general tension which has centred itself in the masticatory muscles, especially the masseten, and overlay dentures should never be prescribed for cases of tcmporo-mandibular joint arthrosis unless definite evidence of occlusal disharmony can be demonstrated. The method of assessing the presence of occlusal disharmony is by means of an occlusal analysis. This is carried out in identically as a chec'l. record for full dentures her Chapter * ) "ilh the difference that models of »he patient's natural caution are used instead of the artificial d-nture*. Chapter XXVIII THE CLEIT PALATE FROM THE PROSTHETIC ASPECT A deft palate may be defined .as a lack of continuity of the lac. U may be congenital he. the individual is born with the bdity or it may be acquired as a result of injury or disease uently a carcinoma spreading from the maxillary antrum), 'liter type of deformity is better referred to as a perfora- ’ihc palate rather than a cleft and will be dealt with 702 CLINICAL DENTAL PROSTHETICS The Occlusal Analysis A face-bow reading is taken to enable the upper model to be mounted on the articulator in the correct relationship to the glenoid foss®. A check record ofsoftwaxis taken with the patient completely relaxed and the teeth closed into but not through the soft wax template. The rationale behind this is that when the mandible is closed from the position in which it is held by the relaxed muscles into the wax, the mandible is following the path which the muscles and the tcmporo-mandibular joints wish it to take. As it is not closed completely through the wax the cusps of the opposing teeth do not come into contact, and therefore no cusp guidance occurs to divert the mandible from the muscle and joint path of closure. If now, using this wax template, the lower model is articulated to the upper model which has already been mounted by means of the face- OVERLAY OR ONLAY DENTURES 703 bow, and the wax template removed, the models can be closed through the two or three millimetres which separate the occlusal surfaces of the teeth with fair assurance that they are following the same path that the patient’s mandible would follow as guided by the joints and muscles. This is because the last few millimetres of closure of the mandible is a hinge move- ment with the condyles acting as the centres of rotation. When the teeth are occluded on the articulator, it can be observed whether or not they interdigitate correctly, or meet in such a manner that a major shift of the mandible is necessary to effect interdigitation. An occlusal analysis of this type is shown in fig. 512. In a case such as this an overlay would be constructed to reshape the occlusal surfaces in harmony with the joint and Fir, 512. - Model* have been mounted on an anatomical articulator by mean* of a chctL record ami face bow am! rioted /ntci the position of loolh contact. It can Lr seen that when futl cloture occurs the mesial incline* of the cusps of the lower teeth will force the mandible to retrude as indicated by the arrows. An overlay can prevent tills tendency to backward displacement. 704 CLINICAL DENTAL PROSTHETICS muscle path of closure of the mandible and thus prevent the cuspal guidance of the teeth forcing the mandible to assume a strained position. General Remarks in Relation to Overlays (1) Overlays should normally be constructed to fit over the upper teeth. The reason for this is that by carrying an acrylic platform behind the upper incisors a surface is presented with which the tips of the lower incisors can occlude, and this prevents any possibility of their over eruption (see fig. 508(6)). The contact of the acrylic with the palatal surfaces of the upper incisors also prevents their over eruption. If the overlay is constructed over the lower teeth, in order to prevent over eruption, it is necessary to cany the acrylic over the incisal edges of these teeth, and this produces an unsightly appearance which is altogether avoided with an upper overlay. (2) Overlays should not normally obliterate the free-way space, although their presence wall obviously reduce it, and they should never be built higher than is absolutely necessary. Some individuals will be found to have so small a free-way space that the fitment of even a shallow overlay w ill completely obliterate it. In these cases it is sometimes found on fitting an overlay of normal dimensions that after a short time a free-way space develops again. This may be due cither to the fact that in the first instance the individual was never fully relaxing the mandible, and therefore giving an inaccurate recording of the true free-way space, or the presence of the overlay has caused the teeth to be depressed into the ridge. This latter occurrence the authors view with concern although in some instances no untoward symptoms has developed from such a happening. In some cases relief of symptoms has been achieved by the use of the overlay sufficiently to warrant its retention. (3) In a case in which it is considered that an overlay might be a suitable form of treatment, the first appliance should be constructed in aery lie resin. Such an appliance might be termed a diagnostic appliance. If after the initial period required for getting used to it, it is worn by the patient with comfort and OVERLAY OR ONLAY DENTURES 705 abatement of the symptom for the cure of which it was fitted, then it can be assumed that it is a suitable form of treatment, and can be replaced in due course by a metal overlay. The metal appliance is more robust and long-lasting than the acrylic one, as the latter tends after a few months to wear and disintegrate. If on the other hand no improvement of symptoms occur after a few weeks wear then the acrylic appliance may be dis- carded and no great loss of time or effort will have occurred. (4) It is important that overlays and the teeth under them are kept scrupulously clean by the wearer. If they arc not then caries is likely to occur. Chapter XXVIII THE CLEFT PALATE FROM THE PROSTHETIC ASPECT Definition A cleft palate may be defined as a lack of continuity of the palate. It may be congenital i.e. the individual is born with the disability or it may be acquired as a result of injury or disease (frequently a carcinoma spreading from the maxillary antrum). This latter type of deformity is better referred to as a perfora- tion of the palate rather than a cleft and will be dealt with separately. Deielopment For full details of the development of cleft palate the reader is referred to the appropriate text; briefly the salient details arc as follows: The Lip. - The upper lip does not develop as a complete entity but is formed by the coalescence of the premaxillary and maxillary growth centres on either side to produce the com- plete lip. Fusion of the sections of the lip developing from each growth centre commences around each nostril floor and spreads down- wards towards the lower border of the lip uniting the pre- maxillary and maxillary processes on each side. Failure of this union will result in a cleft or hare-lip which, depending on the degree of failure of union, may vary from a notch in the lower border of the lip on one side to a complete bilateral cleft of the lip with the prolabium (i.e. the middle segment of the lip) only attached loosely to the nasal septum, the cleft extending up into each nostril [see fig. 513). The Palate. - The palate is developed from the maxillary and premaxillary growth centres, union of the three segments com- mencing at the region of the nasal floor represented in full 706 THE CLEFT PALATE 7°7 Tic. 513. - A unilateral hare lip. (Photograph b) kind permission of Mr. M A. Kettle.) development by the incisive foramen. Union from this point proceeds backwards until both the hard and soft palates and uvula have united, and forwards along the line of the future maxillary premaxillary sutures eventually uniting with the developing Up on either side. Failure of union at any stage will result in a cleft palate ( sre fig. 514) which may be prc-alvcolar i.e. a hare-lip; post- alveolar i.c. a cleft palate varying from a bifid uvula to a com- plete failure of union between the two halves of the soft and hard palates up to but behind the incisive foramen, or alveolar which is a cleft palate involving the soft and hard palates and dividing the alveolar process in the region of the lateral incisor Fig. 514. (a) Post alveolar or Veau Class I cleft of palate. (Photograph by kind permission of Professor Malcolm Gibson.) ( 4 ) Alveolar cleft or Veau Class III. THE CLEFT PALATE 709 Fia. 515. -Dolled circle indicate* area of initial union of segments forming palate and lip; union then proceeds in directions or arrows. If no union occurs and j, 2 and 3 are patent a bilateral hare lip with a complete alveolar cleft results. If 2 and 3 unite and 1 is patent then a post alveolar cleft results Union may proceed part way along 1 and then stop tooth, continuing into a cleft lip on one or both sides ( see fig. 5 'j)- Classification of Cleft Palates A more detailed classification of cleft palates and one that is generally accepted is that of the famous French plastic surgeon, Victor Vcau, which is as follows: Class I. Clefts involving soft palate only. Class II. Clefts involving soft and hard palates up to incisive foramen. Class III. Cleft of soft and hard palates, right forwards through alveolar ridge and continues into lip on one side. Class IV. Same as Class III only associated with bilateral hare-lip. 710 CLINICAL DENTAL PROSTHETICS The cause of failure of union of the growth centres which produces a cleft lip and palate is unknown, although many suggestions such as vitamin deficiency, malnutrition, defi- ciencies in the embryonic circulation have been advanced. The incidence of cleft palate varies slightly in different areas of the world but the accepted average is one in a thousand births. Fogh Andersen has produced figures showing that cleft palates are of more common occurrence in girls and cleft lips in boys and that the left side is more frequently affected than the right. Disabilities Occasioned by the Presence of a Cleft Palate The basic disability of a cleft palate from which all the others stem is that the individual is unable to close at will the naso- pharynx from the oropharynx. In the normal individual this closure is effected by the complete hard palate and by the raising of the soft palate into intimate contact with the posterior and lateral pharyngeal walls (see fig. 516). This airtight THE CLEFT PALATE 7II separation of the two cavities is essential to the functions of normal swallowing and speech. The Action of Swallowing In swallowing, the food bolus or liquid mass is held in the depressed centre of the tongue the sides of which are pressed hard against the lateral aspects of the hard palate. Peristaltic- likc waves then travel along the tongue from before backwards and propel the food or liquid towards the pharynx. The soft palate which is already raised into contact with the walls of the pharynx prevents its escape into the nose and directs it towards the oesophagus; the pharyngeal walls contracting to propel it on its way. The Problem of Suckling an Infant when the Palate is Cleft If both the hard and soft palates arc cleft the natural process of swallowing is impossible and the first problem facing those nursing a child born with a cleft palate is concerned with its feeding. A normal child when suckling takes the nipple and part of the breast into the mouth, the nipple resting on the back of the tongue. The alveolar ridges acting with a chewing action express the milk which is deposited on to the tongue and then swallowed. With breast feeding very little, if any, sucking which requires a negative pressure in the mouth is used. With bottle feeding, however, a sucking action is frequently necessary because the design of many artificial teats make it difficult for the action of the ridges alone to express the milk. To produce a negative pressure in the mouth requires a complete soft palate in intimate contact with the walls of the pharynx otherwise air will enter the mouth through the back of the nose. The Action of Swallowing when the Palate is Cleft In spite of the problems which face the infant with a cleft palate, in most cases it adapts itself to spoon feeding and sometimes to suckling if the head is turned on one side so that the milk may be swallowed between the tongue and the side of the palate. In the case of a very extensive cleft, however, this is impossible and it may be necessary' to construct an acrylic palate to enable the child to swallow. 7 12 CLINICAL DENTAL PROSTHETICS The Construction of an Acrylic Palate A composition impression is taken of the infant’s upper jaw. This can be accomplished most easily if the child is held on the nurse’s knees with its head towards the operator, who himself is sitting down. To the model, cast from this impression, a simple wax palate is adapted extending to the sulci and two long pieces of stainless steel wire, 2 mm. in diameter, are waxed in place so that they will issue forwards at about the positions of the corners of the mouth after the palate has been processed in acrylic and is in place in the mouth. The wire extensions arc then bent to follow closely the external contouis of the checks and by means of a skull cap or bonnet support, the appliance is held in place, while the child is feeding. If surgical closure of the cleft is unsuccessful or no prosthetic treatment is given, as the child grows it adapts isclf to swallow- ing along the side of the tongue using the posterior third thereof to close the cleft in the soft palate, and soon becomes so adept at swallowing in this way, that little if any food or liquid escapes into the nose. The Technique of Normal Speech The initial sound of speech is produced in the larynx and travels as a vibrating airstream either through the mouth where it is modulated into articulate sounds by the tongue, palate, lips and teeth, or through the nose where the nasal cavities and associated sinuses produce a nasal resonance. The production of the correct sound depends in all cases on rapid and accurate positioning of the soft palate. When speaking, all sounds except for those of m, n and ng, the soft palate is raised preventing all nasal escape of air which is thus wholly directed through the mouth where it is modu- lated in one of three ways. For the vowel sounds the air stream escapes continually through the mouth the shape of which is altered for the various vowels by raising or lowering the tongue and by altering the shape of the exit through the lips. The oral consonants are of two kinds - the stopped conso- nants and the frictives. The sounds of the stopped consonants THE CLEFT PALATE 7*3 are produced by first of all stopping the air stream momen- tarily and then allowing it to escape through a cavity shaped to produce the sound in question. A few examples will make this clear. B and P sounds (labials). - The air stream is stopped momen- tarily by closure of the lips and then released explosively when the lips are suddenly parted (see figs. 517 and 518). T end D sounds (. lingua-denials ). — The stop is made for these sounds by the tip of the tongue being pressed against the palatal surfaces of the upper front teeth. G and K sounds (linguo-palalals). - In these sounds the momen- tary stop is made by the back of the tongue being pressed hard against the hard palate (see fig. 519(a)). Fig. 517. — The first phase of the ‘B* sound. The initial sound is produced in tne larynx and travels upwards on the nirstream bring directed into the mouth by the raised soft palate. The bps are closed and therefore the airstrram is stopped when It reaches them and is held there under pressure. CLINICAL DENTAL PRO'STHETICS 7*4 The friclives or s, z and c sounds. - These are not produced by stops but by allowing the air stream under pressure from the lungs to escape through a finely adjusted slit formed between the dorsum of the tongue and the palate. The m, n and ng sounds . - These are the nasal consonants and are the only sounds produced with the soft palate lowered, allowing the air stream to escape through the nose. In the m sound the nasal route is the only one taken by the air, in the n and ng sounds the escape is partially through the nose and partially through the mouth. Speech Faults when the Palate is Cleft It will be appreciated from the foregoing that the production of all oral sounds requires the airstream to be under some degree of pressure and this can only be maintained and the air- stream correctly directed through the cavities of the mouth if THE CLEFT PALATE the soft palate and pharyngeal walls are producing an airtight seal to nasal escape. In the individual with a cleft palate this is not possible and the airstream escapes through the nose. In an attempt to prevent this the back of the tongue is thrust into the cleft and if the treatment of the cleft either by surgical or pros- thetic means is delayed much after the second year (which is the age when rapid speech development occurs) this tongue habit becomes well established and even after treatment has been given makes correct speech difficult, because as has already been observed the tongue is a potent factor in the shaping of the modulating cavities and its free play especially forwards is vital to good speech [see fig. 519 (b)). The Effect of a Cleft on Appearance The effect of a cleft on the appearance of an individual will depend on whether the lip is cleft as well a3 the palate. 7 16 CLINICAL DENTAL PROSTHETICS Fig. 51 g (6). - Dotted line shows how the tongue and upper teeth should make the 'stop’ for the ‘T sound but the palate is deft and therefore the vibrating airstream escapes through the nose: in a vain effort to present this escape the individual with a deft palate pushes the tongue into the pharynx (continuous line) and thus develops a major fault of tongue position and thus of articulation. (fl) When the Lip is Cleft. - The cleft in the lip may be uni- lateral or bilateral and the prcmaxilla may be detached entirely from the maxilla in bilateral clefts. The cleft of the lip will involve the alveolar process and in most cases the lateral incisor tooth will either be missing or deformed. The cleft in the lip will be repaired surgically usually about six weeks after birth, and most present day operations result in A functional lip of good appearance, but a repaired lip will bring more tension to bear than a normal lip on the anterior max- illary ridges and the teeth as they erupt frequently producing an occlusal relationship of Angle class III type and if the lateral THE CLEFT PALATE 717 incisor is missing a closing of the gap (see fig. 520). Orthodontic treatment will be necessary to restore the form of the arch and bring the teeth into correct occlusion with the lowers which will not have suffered any deformity. Thereafter a simple denture will be necessary to maintain the expansion and replace the lateral incisor. (A) When the Hard Palate is Cleft. - If the cleft in the hard palate is repaired surgically there is nearly always a reduction in the lateral and forward growth of the maxillae as a result of the tension in the scar tissue of the repair. Orthodontic treat- ment will reduce this contraction of the arch and in doing so frequently open up parts of the cleft. A denture is necessary to maintain the expansion and cover the open cleft. Modern atraumatic surgery has reduced the resulting con- traction of the arch which formerly occurred but it is essential that orthodontic treatment is instituted early and is maintained. If for some reason no orthodontic treatment is given severe deformity of the maxilla may result. Even severer deformation Fig. Contraction of upper arch following *urgery. (Right) Orthodontic treatment has restored the shape or the arch but opened up the deft in the hard palate "tuen can be very simply covered by the denture requited to replace {2 which is congenitally missing. {Photograph by kind permission of Mr. D. F. Glass.) 718 clinical dental prosthetics is seen in older individuals who were operated on by the more traumatic surgical techniques employed earlier in the century. The results of such operations are seen in figs. 521 and 522. The effect of these on the appearance of the individual is marked; the middle third of the face is flattened and contracted ( see fig. 523). The deformation resulting from uranoplasty (hard palate repair) is made worse if the lip repair was poorly done and has resulted in a tight immobile lip. The Prosthetic Treatment 0/ Cases with Contracted and Deformed Dental Arches The treatment of patients with this condition if they are past the age when orthodontic treatment is likely to be effective is to construct a denture which covers the misplaced teeth and set the artificial teeth in a fresh arch corresponding to the position and form of the normal {see figs. 524-527). The lower jaw will usually not have suffered any deformation and if the artificial teeth are set to occlude with the lower teeth a \erv Fig. 522. - Contraction of arch with breakdown of tissue following surgical closure of cleft (patient is too old for orthodontic treatment). Fio. 523. - Flattening office and contraction of lips following surgery. THE CLEFT PALATE 723 upon this will usually be performed before the end of the second year because it is between the second and third years that the child really commences to talk and if repair is delayed beyond this time faulty habits of speech will have developed which are so difficult to eradicate. If it is decided that surgery is unlikely to be successful then it is at about two years of age that the first obturator should be fitted. Details of this are given later in the chapter. Finally when the question of the treatment of the lip and soft palate has been decided consideration should be given to the repair of the hard palate. This is the least important problem of all because the cleft in it can be covered so easily and with extremely successful results by means of a simple acrylic or metal palate. If the cleft in the hard palate is at all wide its repair by surgery will almost certainly result in contraction of the dental arch and maxilla and the cleft will be reopened by the subsequent orthodontic treatment. The Prosthetic Treatment of Soft Palate Clefts The treatment of clefts in the soft palate is by means of an obturator which means simply something which closes a cavity (Latin, obturare: to close) {see fig. 528). Such an obturator is sometimes called a speech bulb. Its method of function and its form will be fully described later but basically it is a smooth acrylic bulb lying in the plane of maximal pharyngeal contrac- tion so that when the pharynx is relaxed there is a space between it and the bulb allowing free passage of air to and from the nose and when the pharynx is contracted it grips the bulb producing an airtight seal of the nasopharyngeal isthmus (fig. 540). Types of Obturator Obturators arc of 3 varieties, (a) Fixed pharyngeal (fig. 528) ; { b ) hinged pharyngeal; (c) Meatal. The fixed variety is an extension of a denture projecting into the pharynx at about the level of the anterior arch of the atlas * e general »hape of lht» tbn t,f obturator. Fio. 5 |i(4)- FlO. 54 1 (4). The lower photograph shows a eleft winch lias had surgical treatment which has only been partially successful and tlic soft palate remnants are fibrosed and inactis e. The tipper photograph shows the pear shaped ty pc of obturator which ts usuaffy smfahfe lor c/osittg such a clrft and (hr line diagro m shows the general shape of this type of obturator. Tia. 541(c). FlO. 541(f). The photograph on page 740 shows a cleft tn which the soft palate has apparently been successfully united surgically . The palate howrser is loo short to make contact with the posterior pharyngeal trail Tltc photograph on page 741 shows an obturator for this type of case, united to the denture across the soft palate bv a tailpiece. Tlie line diagram shows the general shape of this type of obturator. THE CLEFT PALATE 743 Fig 5-4 «(553. - rrr-opcratkc palate* for fenctirolion caw?. fn' With a wire loop in earn' gutta-percha. ( 4 ) With Viiallium irron for fixing in the lx>nr of ih«* mtdbnc of the palate. (r) Plate ( 4 ) in place in mouth. Tliii type of fixation 1* nnl> rarely called for when extensive vttrgrry prevents simpler methods of fixation brine; used. palate is inserted and held in place by gum tragacanth or, in extreme ease, by Vitallium screws placed in the midline of the palate (see fig. 553). The purpose of this appliance is to enable the patient to speak, cat and drink normally. As soon as the wound has healed sufficiently and is no longer painful an alginate impression is taken in a special tray, care being taken to ensure that excess alginate does not flow into the nasal cavities and become locked therein so that it remains SURGICAL PROSTHESIS in place on removal or the main impression {set fig. 554). Judgment or the amount nr impression materia! used is the simplest way to ensure this, but Vaseline gauze can be packed into parts or the nasal cavity ir necessary. On the model cast from this impression an acrylic base-plate is constructed to the normal outline or an upper denture and penetratinginto the cavity for as short a distar.ee as is necessary to produce a seal. On this base-plate the records and try-in arc carried out and then the denture is finished by processing teeth to the base-plate with cold cure resin so as not to warp the base-plate by heat. The retention of the denture will depend to some extent on the size of the fenestration wound. If this is small the denture can be retained normally by adhesion and peripheral seal, although this latter is naturally reduced, and tongue control. 772 CLINICAL DENTAL PROSTHETICS In cases presenting a large wound, springs arc usually successful. In cases of extreme loss of tissue, such as shown in fig. 555 Adhere the whole of the palate was removed, the appliance requires to be made hollow to reduce its weight. This is achieved by the use of a plaster and pumice core. Facial Prostheses Any part of the face may need to be replaced by a prosthesis, either as a temporary measure prior to plastic surgery or as a permanency. The technique is briefly as follows: An impression is taken of the area surrounding the missing parts. This may need to be done in plaster, alginate or a combination of the two. If the Fw-355- (a) A simple denture for a fenestration ease with little penetration into the cavity because stability and retention are good, (A) from the side. (<) A denture with complete penetration into the cavity because stability was scry poor without it. This type of obturator roust be hollow to reduce weight and hate a tube to facilitate nasal breathing. (< i) A large obturator made for case 532(A) hollow and will, springs for retention. SURGICAL PROSTHESIS 773 774 CLINICAL DENTAL PROSTHETICS F'o. 555 s d). tissues to be impressed arc firm and unyielding or part of the nasal cavities with undercut areas need to be included in the impression, then alginate is the material of choice. If the tissues arc soft and mobile then plaster should be employed, for alginate will distort such tissues. Fig. 556 illustrates the preparation of the patient prior to the impression, so that plaster docs not become entangled in the eyebrows and lashes, and the taking of a combined alginate and plaster impression for the making of a prosthesis to replace part of the nose and the upper lip. In the case illustrated alginate was first introduced into the nasal cavities and allowed to set and then plaster was gently poured and shaped o\cr the outside of the nose and facial surfaces with the patient supine. The impression is shown in place in fig. 556. A model is cast to this impression and on this model the missing parts of the nose and Jip are fashioned in plasticine SURGICAL PROSTHESIS 775 Fio. 556. - Plaster impression being taken for patient illustrated in fig. 558. {see fig. 557). This model is then duplicated and cast in plaster and on this plaster model a thin sheet of casting wax is laid and moulded to reproduce all the contours. The use of negative cores is sometimes a help in achieving this. This wax template is then finally fitted to the master model from which the plasti- cine has been removed and then processed in clear acrylic resin. This results in a very thin, completely clear, template of the correct shape of the missing parts. This is tried on the patient’s face and, if acceptable with regard to shape and fit, is coloured on the under-surface with artists’ oil paints. These can be mixed at the chairside and painted on and removed until the correct shade and match to the patien t’s skin is obtained. Tire paint is allowed to dry foe 0 few days and then sandwiched between the original template and a layer or cold cure acrylic which is painted thinly over the dried paint. This type of appliance can produce an excellent colour match and is clean, as it can be washed; it is very light and adequately durable and simply replaced if the models are kept. 7/6 CLINICAL DENTAL PROSTHETICS Fig. 557(6}. - Plasticine nose and lip in process of brine fashioned in this model. SURGICAL PROSTHESIS 777 The polyvinyl chloride prostheses, however, have the advantage or resiliency and are frequently preferred by patients for this reason. Basically, polyvinyl chloride for dental use consists of a mix- ture of ‘Come. S.U.’ powder sold by I.C.I. together with an equal weight of dibutyl phthalatc plasticizer which is then heated in the plaster mould to a temperature of 147 5 C. This temperature is critical, if only slightly exceeded burning of the final product ensues. To reduce the danger of charring a small quantity (about 10 per cent by volume) of calcium stearate is included in the mixture. Processed P.V.C. is translucent and human tissue is semi- opaque, therefore a variable quantity of an opacifier is also required and this may be either zinc oxide or titanium oxide powder and the quantity should be varied to suit the part being made. The colouring of polyvinyl chloride prostheses to match the surrounding tissue is not simple and trial and error, using test pieces of P.V.C., is necessary to achieve a satisfactory result. Dyes arc produced by I.C.I. in the form of powders which may be mixed with the dibutyl phthalatc: a selection is as follows: I.ithafor Red A.S. Waxolenc Red O.S. Waxolcnc Green G.S. Waxolenc Blue Lithafor Yellow A.S. Lithafor Brown A.S. The dyes should be made up separately in a concentrated solution with dibutyl phthalate and the required number of drops of each put into the clear plasticizers with a pipette before mixing in the powders. Final colouring of the prostheses may be achieved after processing by reducing excessive colouring by rubbing the surface of the prosthesis with a pad of cotton-wool soaked in acrylic monomer. Extra colouring may then be added by working in various dyes dissolved cither in acrylic monomer or dibut)l phthalate on a pad. 778 CLINICAL DENTAL PROSTHETICS Fig. 558 (a and 4 ). -Patient who has lost nose and upper lip. Facial prostheses can, in most instances, be retained b> a pair of spectacles (r« figs. 558 to 561) and if the patient docs not need glasses for vision plain lenses are employed. Ho. 559 r »). - Denture in place for patient illustrated in fig 558. Note breathing tube. CLINICAL DENTAL PROSTHETICS 78 4 IJp Splints Paralysis of the seventh crania! nerve is a fairly common occurrence. It may result from trauma, surgery, or sometimes occurs spontaneously. Its duration may be permanent or tem- porary. It results in flaeddity of the muscles of facial expression on the side affected. Frequently the physidan or surgeon in charge of the patient requests the construction of a splint to support the lip. Such a splint is conveniently attached to a denture or, if the patient has all his natural teeth, to an acrylic palate. The splint is made of cold cure acrylic and attached to a wire loop or to a removable rod and should be adjusted to fit at the comer of the mouth and support the lip in its norma! position, that is, level with the opposite functional side (ste fig. 562). Chapter XXX IMPLANT DENTURES Ever since prosthetic dentistry became an entity practitioners 1 have sought for a means of increasing the retention, stability, efficiency and comfort of dentures for those patients presenting grosslv absorbed edentulous ridges. The life of such individuals is often made miserable by the continual instability of their dentures or by the pain engendered through pressure on friable mucosa overhang an irregular bone surface or on a mandibular or mental nerve which has come to lie submucous!} as a result of the excessive absorption of the alveolar ridge. It has long been obvious that were it possible to anchor a denture in such cases to the bone by means of a metal insert that a great deal could be achieved. Such a metal insert attached to the surface of the bone with abutment posts penetrating die mucous membrane is termed an implant and during the last century many spasmodic attempts have been made with a variety of metals and alloys, employing a large number of techniques, to perfect such implants. Metal teeth with fenes- trated roots made of lead, gold, platinum, silver and stainless steel have been inserted into tooth sockets after extraction. All these failed because the implant was rapidly exfoliated. One of the main reasons for this failure was the clcctrolvtic incompatibility of such metals and allo)S with the body tissues. This major disadvantage disappeared with the advent of the chrome cobalt alloys, such allovs being clectrolytically inert as discovered by Venable and Stuck (1936). The usefulness of these alloys in surgery and their compatibility with the body tissues was first utilized by the orthopaedic surgeons who used Vitallium as plates and screws for positioning the ends of fractured bones. About fifteen jears ago serious attempts were made by dental surgeons to develop a method for implanting chrome ; robali structures into the jaws which would provide a f 78s 7^6 CLINICAL DENTAL PROSTHETICS stable base to support dentures in cases presenting major prob- lems of stability or discomfort. The first subperiosteal implant was placed by Dahl of Sweden in 1943 and this was followed by GershkofT and Goldberg in 1948, and in Great Britain by Mack and Trainin in 1952/53. • From the earliest attempts to the present day there bate been many successes and many failures and many techniques have been tried and modified or abandoned. At the present time however as the result of the work of a comparatively small number of pioneers, a technique for making and inserting a •chrome cobalt implant has been developed which is sufficiently reliable to employ in those cases in which all other normal methods of providing comfortable and efficient dentures have failed, and the following pages give in outline form the stages of this technique: The Technique of Making and Fitting a Lower Chrome Cobalt Implant The normal prosthetic procedure for constructing full upper anil lower dentures is carried out until the dentures have reached the ‘try-in’ stage. At this point the occlusion and appearance of the dentures arc carefully checked and if approved (he upper denture is finished in the normal way, the lower denture being retained in the waxed up stage. In the laboratory the first molars and the canines are removed from the waxed up lower denture and a sharp instrument is thrust through the wax in approximately the centre of the areas occupied by these teeth until it penetrates the surface of (he ridge of the plaster model beneath sufficiently to mark it (see fig- 563). These marks on the model locate the positions of the abut- ments of the future implant. A piece of base plate wax is next adapted to the ridge of the model and contoured to the shape of a denture base and then withdrawn and processed m clear acrylic. It is replaced on the model and small holes are drilled through it in the areas marked for the future abutment (see fig. 564). The purpose of this acrylic template will become apparent in due course. Next two special trays are made to fit the model of the lower Tic. 564. -Clear acrjl'C template, fitting lower mode!. »nh holes bored. 788 CLINICAL DENTAL PROSTHETICS ridge extending buccally and labiallv. These trays may be constructed in swaged German silver or light cast tray metal. They will be used to take the impression of the bone when the mucous membrane has been reflected. An acrylic record block is also constructed to the lower model to occlude with the finished upper denture. Rims arc only built in the premolar and molar regions, and wire staples arc inserted into the acrylic in the premolar regions to facilitate its manipulation. This record block will be used lined with gutta-percha to record the jaw relationship when the mucous membrane has been reflected so as to enable the models of the bone impression to be correctly articulated in relation to the upper denture. The Exposure of the Bone and the Taking of the Bone Impression If an implant is to be successful it must fit the surface of the bone accurately and for this to be possible it must be con- structed to an impression of the bone itself, therefore, the fitting of an implant demands two surgical stages. The first consists of the reflection of the mucous membrane followed by the taking of at least two impressions of the surface of the bone, together with the recording of the occlusion, also taken with the record block fitting the bone. The second stage which is usually carried out about three weeks after the first operation consists of the reflection or the mucous membrane and the insertion of the completed implant. The First Operation For this the acrylic template, the special trays, the acrylic record block and the finished full upper denture are needed, together with all those surgical instruments usually employed for the reflection of mucous membrane and its stitching together again. In addition some composition, gutta-peicha and rubber or silicone base impression material is required. The patient is prc-mcdicatcd and the mandible anacsthetbcd with double mandibular and long buccal injections. (It is possible to perform this operation under general anaesthesia IMPLANT DENTURES 789 but a local is preferred because the co-operation or the patient is helpful.) The clear template is positioned on the surface of the lower ridge and the point of a probe thrust successively through the holes in the template. This action produces four bleeding points corresponding to the location of the future abutment posts. Next the thickness of the mucous membrane at the site of the bleeding points is measured using a probe with a sliding rubber washer on it. A tungsten carbide round bur size No. 3 is now sunk into the bleeding points and shallow pits drilled into the surface of the bony ridge. The purpose of these pits is that they will be recorded in the impression of the bone and thus in the model cast from this impression, and locate clearly the positions of the abutment posts. It is important that a tungsten carbide bur is used because a steel bur might leave small steel particles in the pits in the bone and these could produce an electrolytic action with the implant which might be sufficient to imalidate it. Next an incision is made on the crest of the ridge com- mencing at the retromolar pad of one side and passing succes- sive!) through each bleeding point and finishing at the opposite retromolar pad. Cross incisions are made lingually and buccall) m the retromolar pad regions and in the mid-line. The muco- periostcum is now carefully reflected to expose the mylohyoid ridges, the external oblique ridges, the genioid tubercles and the mental nerves which are carefully identified. As wide a reflec- tion of the mucous membrane as possible is desirable. The reflection complete, the surface or the exposed bone is examined and any sharp or rough areas smoothed with a bone file (set fig. 565). Taking tiie Bone Impression The next operation is the taking of the bone impression, and on its accuracy success or failure of the implant to a large extent depends. If the substructure of the implant is a close fit over as wide an area of the bone as possible, it will posses an inherent stability w'hicli is all important. To facilitate the insertion of the impression tray the lingual mueoperiosteal flaps are joined with sutures passing under the 79o CLINICAL DENTAL PROSTHETICS T»c. 563 - Murom mrmbranr rrflrrtrtJ and Uw rxpxrri Note sharp Ictlgr* of bone which were rnnmril pnnr to taking imprcwon and holes bored in surface of Ixme in 3(3 region. (Photograph b> kind prnniwion of Mr. M. A. Kettle.) tongue, and when the sutures are looped and pulled tight the lingual flaps arc retracted. The impression tray is non tried in. Its insertion is simplified if it is inserted under the buccal flap of one side first, and then rotated into position while the opposite buccal flap is elevated out of the way. The front part of the tray being seated finally while the labial flap is retracted. The tray should cover the whole of the bony region, and should only be trimmed if too large. An o\cr extended bone impression is far belter than an under extended one. The tray is withdrawn and loaded with composition of an even thickness (about ji in.) and reinserted in the manner previously described for the empty tray. before seating the composition fully into place any muroperiosteal flaps which have been trapped under its edges must be care- fully retracted. When fully in place the composition is chilled IMPLANT DENTURES 79 1 with a jet of sterile iced water. When set hard the composition is removed and inspected. It should show impressions of the mylohyoid ridges, the external oblique ridges, the mental nerves and the genioid tubercles, and should be well extended over the labial surface of the ridge. The surface of the compo- sition is now carefully dried, and then covered with an even thickness of mixed rubber base or silicone impression material and again inserted and held in place until the impression material has fully set. The composition stage can be omitted and the rubber base material used alone if desired. A typical com- pleted bone impression is shown in fig. 566. A second bone impression is then taken. It is essential that two impiessions are taken because it is difficult to assess their a bsolute accuracy and therefore it is a safe precaution to have two implants made, one to each impression. If facilities allow it is wise to have the models cast to these impressions while the occlusal recoid is being taken and then the models checked visually with the surface of the bone before suturing the flaps together. After 792 CLINICAL DENTAL PROSTHETICS the impressions have been taken and the wound cleaned of any small pieces of impression material which may have remained in place, the fitting surface of the acrylic record block is lined with softened black gutta-percha, and a little soft wax placed on the occlusal surfaces of the blocks. The gutta-percha is located on the bone surface and the patient instructed to relax and close the softened wax gently against the teeth of the finished upper denture s\ hicli has pres iously been irserted (see fig. 567). The positioning anti stabilizing of the record block is facilitated by inserting the fingers into the wire staples in the pre-molar regions of the block. The final stage of the first operation is the careful approximation of the mucoperiosteal flaps with sutures. IMPLANT DENTURES 793 Fig 567(A). A Brief Outline of the Laboratory Procedure for Producing an Implant (1) The model of the bone (fig. 568) is articulated with die upper denture by means of the record block. (2) The model is duplicated in chrome cobalt investment material. (3) The substructure of the implant is outlined on this model. The abutment posts arc positioned as indicated b\ the small location pits in the model and the bars of the frame-work arc kept as narrow as possible commensurate with strength. The periphery of the frame-work is located on or over the external oblique ridges, and well short of the mylohyoid ridges, because if it protrudes lingually beyond these structures it will ulcerate through the thin lingual mucosa. It is kept well clear of the mental . nerves and is carried as deeply as possible down the labial surface of the ridge. The struts joining the abutment posts to the periphery of the framework are kept narrow and the spaces between them wide. Any additional struts required for strengthening the substructure should be as few as possible and little or no metal should be placed in or across the incision line. The proposed outline of a typical implant substructure framework is shown in fig. 569. 79-J CLINICAL DENTAL PROSTHETICS IMPLANT DENTURES 195 (4) The implant is waxed up to the proposed outline set fig. 570). The abutment posts should be shaped as shown in 571 withaneckofal to 3 mm. diameter and ofa depth ofslightly greater than the thickness of the mucous membrane (when the mucosa is no longer subjected to the pressure of the fitting sur- face of a denture, its thickness will increase slight!) ). The height of the abutment posts above the mucous membrane should be such that they will be well short of the occlusal surfaces of the upper teeth. This height can be gauged from the articulated model and upper denture. The diameter of the base of the abutment posts should be about 4 mm. in the canine regions and 6 mm. in the molar regions and each post should ha\e a 5 degree (approx.) taper. The patterns of the posts can be made m either wax or acrvlic resin. Casting of the pattern is carried out in die normal manner and care should be taken to use only an alloy which has been proved to be clectrolyticallv compatible with the bod> tissues. The cast implant is trimmed and finished, the substructure being left with a sand blast surface, and the abutment posts Wax pattern for substruct acrjltc resin turned on 1 796 CLINICAL DENTAL PROSTHETICS A B C D Fig. 571 -Silhouettes of shapes of implant posts all liave approximately a 5 degree taper. a. Canine post, dimensions are: diameter at base 4 mm , diameter of neck joining it with substructure sj mm. b, Molar post, diameter at base 6 mm., diameter of neck 3 mm. C, Illustrates an aticmauvc shape to provide a ledge to support the superstructure and provide extra protection for the gingival margin. d, Illustrates a post with a neck in it to engage a clasp if required The dimensions given are arbitrary; the height of the neck will be slightly more than the thickness of the mucosa ; the height of the post w ill depend on the interalveolar distance. IMPLANT DENTURES 797 and necks highly polished (see figs. 572, 573, 574}. The rationale behind this is that the substructure becomes surrounded and embedded in the periosteal fibres which reattach themselves to the bone surface, and it is considered that they will grip a slightly rough surface best, while the epithelium which* is in contact with the necks of the posts is irritated least by a smooth surface. Mack (tg6o) has shown in experiments with monkeys that it is probable that the whole implant substructure becomes in time surrounded by epithelium and if this indeed proves to be the case it might be better practice to polish highly the whole of the implant. Before finally finishing and polishing the implant it must be carefully inspected visually for imperfections likely to weaken it, and then X-rayed for evidence of any internal porosity. (5) The implant is positioned on the model and the sub- F,o. 573. - Finished unpJanf. Note wide coverage of sub- structure, area of incision left free from metal, clearance of mental nmes and lltat the substructure is short of the mytohyoid ridge. Fl« 574 - Implant on model anicuhtrd bv means of records taken at operation. Note clearance between lops of posts anti occlusal surfaces of teeth of upper denture. structure covered with a thickness of base plate wax of approxi- mately twice the thickness of the mucous membrane. Thimbles arc then waxed to fit the abutment posts and joined by wax bars. The whole is cast in chrome cobalt and then trimmed to be a comfortable and inert frictional fit on the four abutment posts (w fig. 575). This superstructure frame work is an important part of the implant because it confers additional rigidity to it by its close fit to the abutments, joining them by the rigid connecting bars. The connecting bars also ensure that when the superstructure is processed into the lower denture that the contraction of the acrylic will not distort the position of the thimbles and therefore ensures that the denture will be a stable fit on the abutment posts. Two of these superstructure castings arc required for each implant; one is processed into the initial denture and one kept for use with the final denture. (6) The cast superstructure is seated on the abutment posts IMPLANT DENTURES 799 and the initial lower denture is waxed up around it. This denture carries six anterior teeth, but the posterior teeth arc represented by blocks built to occlude with the molars and pre- molars of the upper denture (see fig. 577). The reason for this is that such a procedure simplifies any occlusal adjustment winch may be necessary after the fitting of the implant and the flat surfaces of the lower blocks cause little or no lateral drag to be applied to the implant. Same operators dispense altogether with the initial denture and fit no lower denture until the tissues have healed around the implant. Fitting the denture to the implant as soon as it is placed has two advantages; firstly it covers the wound, protecting it from the inquisitive tongue, and secondly and perhaps more important each time the patient occludes it tends to scat the implant firmly on to the bone surface. The waxed up initial denture is processed in acrylic and then finally shaped and polished. The shape of an implant supported denture has no relationship to that of a normal lower denture. Coo CLINICAL DENTAL PROSTHETICS 1 it:. 577. —The denture fill'd at the vxont) operation in place on implant. Xoie wide clearance between it anti substructure lo allow for thickneM of tnurtrsa. IMPLAS'T I5ENTURES 801 Firstly its fitting surface must be clear of the mucous membrane by at least one millimetre because it is supported entirely by the abutments, and secondly its bucco-lingunl and Jabio- lingual bulk must be minimal and it must lie as accurately as possible in the volume of the neutral space. This is of vital importance because the success of the implant depends to a large extent on its not being subjected to continuous antero- posterior or lateral forces. Such continuous forces arc likely to develop if for instance the denture is shaped so that the lip or the cheek bring a constant pressure to bear on it, not counter balanced by the tongue. Such unbalanced forces will cause the implant to move backwards or sideways with possible loosening of it. If, however, the denture is placed in the neutral zone the forces applied around its periphery will cancel one another out and it will remain in position. The shape of a typical implant supported denture is shown in fig. 578. The Insertion of the Implant This usually takes place about three weeks after the first operation. The patient is prc-mcdicalcd and the mandible Fir.. 578. -An implant Supported denture \irwrti from below. Note narrowness, especially labialh and in region of nwlioln. 802 clinical dental prosthetics anaesthetized as for the initial operation. The mucous mem- brane is incised following the line of the original incision which will still be visible. The second incisions posteriori}' and in the mid-line are not usually necessary. The mucopcriostcum is reflected but not so widely as previously, and as soon as it has been retracted sufficiently from the bone one of the im- plants which have been previously degreased in trichlorcthylcnc and sterilized is tried-in. It should fit the bone surface accurately all round the area of the frame work and lie completely inert when pressure is applied to each abutment post successhcly (see fig. 579). If the first implant does not fulfil these require- Fie. 579. - Implant in pbee prior to suturing of mucous membrane. (Photograph by kind permission of Mr. M A. Kctlfc.} ments in any particular, the second one is tried-in and the more suitable of the two selected for insertion. Some authorities advocate the initial stabilization of the implant by fixing it to the bone by screws placed one in the molar region on each side, and one in the region of the symph\sis. The technique here described docs not employ screws, and provided the extension of the implant frame work is adequate and its fit accurate the}’ do not appear to be necessary. When the implant has been positioned, the muco-^ periosteum is carefully united with sutures (see fig. 580). * Fig. 581. - First denture in place. Note csen occlusal contact has been obtained by cold cure acrylic on surface of posterior blocks. 802 clinical dental prosthetics anaesthetized as for the initial operation. The mucous mem- brane is incised following the line of the original incision which will still be visible. The second incisions posteriori)' and in the mid-line are not usually necessary. The mucoperiostcum is reflected but not so widely as previously, and as soon as it has been retracted sufficiently from the bone one or the im- plants which have been previously degreased in trichlorcthylenc and sterilized is tried-in. It should fit the bone surface accurately all round the area of the frame work and lie completely inert when pressure is applied to each abutment post successively (see fig. 579). If the first implant does not fulfil these rcquirc- Fic. 579 - Implant in place pnor to suturing of mucous membrane. (Photograph by kind permission of Mr. M. A. Kellie.) ments in any particular, the second one is tried-in and the more suitable of the two selected for insertion. Some authorities advocate the initial stabilization of the implant by fixing it to the bone by screws placed one in the molar region on each side, and one in the region of the symphysis. The technique here described does not employ screws, and provided the extension of the implant frame work is adequate and its fit accurate they do not appear to be necessary. When the implant has been positioned, the muco- periosteum is carefully united with sutures (see fig. 580). The 804 clinical dental prosthetics initial denture is then placed in position, and its occlusion with the upper denture carefully adjusted to be quite even in the centric position (see fig. 581). This is important for otherwise tilting forces may be applied to the implant. Provided all the stages have been accurately carried out the healing of the tissues over the substructure and around the abutments should be uneventful (see fig. 583). Commonly the wound breaks down in the anterior region and heals slowly by second intention. It is important that while the denture is a firm frictional fit on the abutment posts it is not so tight that undue force is needed to remove it. As soon as the tissues are completely healed the second or final lower denture should be constructed. The second cast super- structure is seated on the abutment posts and an alginate impression taken around it. When the impression is removed the superstructure will be withdrawn buried in the impres- Fin. 5S2. — X-ray photograph* of implants in pfoce (a) Lateral; note extension of substructure up ascending ramus and deep extension of framework labially, bout designed to resist backward pressures of lower tip. IMPLANT DENTURES IMPLANT t>£NTUR£$ Tic. ^85. - Mode| cast from alginate impression Posts are cast in cold cure acrylic. Record block is al»o shown con- taining second superstructure. sion ( see fig. 584). Cold cure acrylic resin is mixed and vibrated into the thimbles of the cast superstructure, and when this is set plaster is cast into the rest of the impression (s« fig. 585). This technique is employed because if plaster is cast into the thimbles it usually breaks ofT when an attempt is made to remove the superstructure from the model. The ridge surface of the model is covered with a thickness of base plate wax to act as a separator and prevent the base of the denture touching the mucous membrane. A record block is then built round the superstructure and the records taken against the upper denture in the normal manner for setting the case on anatomical articulator. From here on the technique is similar for that of a normal denture, except for its shaping which is similar to that of the initial denture (set fig. 586). Careful attention must be paid to obtaining a balanced articulation because all unnecessary lateral or antero- posterior drag on the implant must be avoided. When the final Ho. 586 - finished second denture in place. denture is fitted the initial denture is retained because when the second denture needs replacing in due course the cast superstructure buried in the first denture will be needed again. General Remarks in Relation to Subperiosteal Implants Several thousand implants have been inserted throughout the world during the last ten years. Many of these have been in place and highly successful for five ) ears or more. If an implant is successful the benefit to the patient is most marked. Many implants, however, have been failures; they have become loose and infection has penetrated around the abutment posts, and along the substructure. In many of these the failure is attributed to a failure of one or more of the following important points: (a) Accurate fit on the surface of the bone. (b) Correct outline and adequate extension of the sub- structure frame work. IMPLANT DENTURES 809 (c) Shape of the denture leading to uneven pressure being applied to it by the surrounding muscles or to uneven occlusion. (d) Careless surgical technique. (e) Inserting an implant in an individual whose health was poor as a result of some systemic disease or whose health has degenerated after the insertion of the implant. In some cases although the general healing of the tissues over the sub-structure frame work has been good, in some areas the tissues have failed to cover the metal. In some of these cases a status quo has developed and the implant has remained in place, in others it has had to be removed. An implant is held in place by the periosteal fibres re-attaching themselves to the surface of the bone around the frame work of the substructure and binding it firmly in place. In a well fitting properh extended implant the firmness of this retention is very’ great. ’Why infection does not penetrate between the abutment posts and the mucous membrane is not fully understood. A gingival margin similar in many respects to the gingnal margin surrounding a natural tooth develops, and it is also thought that there is a current of tissue fluid s\\ eeping up from the substructure of implant around the false gingival margins which prevents the ingress of infection. A great deal of experi- ment and research is needed before implants are complete!) understood and evaluated. There is no doubt however, that in successful implants these false gingival margins appear to be perfectly healthy. Bibliography HOOKS Anderson, j. N. Applied Dental Materials. Blackwell Scientific Publication, Oxford. DRASIER, s. Maxillo- facial Laboratory Technique and Facial Prostheses. H. Kimpton, London. BRENNER, M. D. K. The Story of Dentistry. Dental Items of Interest Publishing Co. craddock, F. w. Prosthetic Dentistry. A Clinical Outline. Henn Kimpton, London. DORRANCE, o. N. Operative Story of the Cleft Palate. W. B. Saunders, Philadelphia and London. nsir, E. w. Principles of Full Denture Prosthesis 4th ed. reused Staples Press Limited, London Foett-ANDERsoN. Inheritance or Hare Lip and Cleft Palate. Arnold Busck. FRAJMf, F. tv. The Principles and Techniques of Full Denture Construction. Dental Items ol Interest Publishing Co, Brooklyn, New York; Henry Kimpton, London. CERStlKOFr, a. and goldberc, N. I. Implant Dentures. Pitman, London. 1 ioldsworti 1 , w. j. Cleft Lip and Palate. William Hcinem.mn Medical Books Ltd. KENNEDY, r. Partial Denture Construction. Dental Items of Interest Publishing Co., Brooklyn, New York; Henry Kimpton, London lands, j. s. Practical Full Denture Prosthesis. Dental Items of Interest Publishing Co., Brooklyn, New York; Henry Kimpton, London. undsay, Lilian. Short History of Dentistry. John Bale, Sons and DanicLson Ltd. miller, R. c. Synopsis or Full and Partial Dentures. Henry Kimpton, London. sujrecy; si; e t. vCita? i*!nUwr miu’ ijrcvuV. yoV cul jLivritgstfnw; nditiburgh. OSBORNE, John. Dental Mechanics for Students. Staples Press Limited, London. osborne, j., and lamm ie, o. a. Partial Dentures. Blackwell Scientific Publications, Oxford. 8l2 BIBLIOGRAPHY peyton, F. a. Restorative Dental Materials. C. V. Mosby Co. Ltd. prinz, Herman. Dental Chronology. H. Kimpton, London. schlosser, r. o. Complete Denture Prosthesis. W. B. Saunders, Philadelphia. sicher, h. Oral Anatomy. H. Kimpton, London. skinner, e. w. Science of Dental Materials. W. B. Saunders & Go. swenson, m. o. Complete Dentures. 2nd ed. C. V. Mosby Co., and Henry Kimpton, London. TUCKFIELD, w. J. Full Denture Technique. Ramsay Ware Publishing Pty., Melbourne, Australia. PERIODICALS Aesthetics and Appearance ASPIN, M. E., TOMLIN, H. R., and OSBORNE, J. (i960) Brit. Dent.J., 109, 27!-274. clark, e. u. (1947) Selection of tooth colour for the edentulous patient, J.A.D.A., 35, 787-793. frusii, j. p., and fisher, r. d. (1955) J.P.D., 5, 586-595. {1956) 6, 160-172. ( 1956 ) J.P D; 6 , 441 - 449 - (1957) 3-P-D-, 7.5-»3- (1958) J.P.D., 8, 558-581. (1959) J-PD-> 9. 9»4-92i- FURNAS, i. l. (1936) Esthetics in full denture construction, J.A.D.A., * 3 ’ 3 “* 3 - . hardy, 1. R. (1939) Wap and means of avoiding obvious artificiality, J.A.D.A., 26, 1289-1291. MENDELSOHN, \v. a. (1938) Light as related to matching shade? of teeth, Dental Digest, 44, 12-14. pound, e. (1951 ) J.P.D., x, 98-111. ('954) ,7-PJ)., 4. fi | 6- YOUNG, II. A. (I954) J-P.D., 4, 748-760. (1956) J-P-D., 6, 743—755- warburtov, w. l. (1946) Pre-extraction records. Dental Survey, 22, 2069-2073. Alveolectomy bowden, A. c. (1943) Indications for alveolectomy and the tech- nique of the operation, D. Gazette , 9, 289-293. cash, 11. r. (1944) Surgical treatment of abnormal soft tissue ridge attachment, Australian J. D., 48, 141-143. Fleming, w. e. {1944) Surgical preparation of the mouth for prostheses, Australian J. D., 48, 197-199- Articulation BIBLIOGRAPHY 813 CRADDOCK, f. w. (1949) Accuracy and practical value of records of condylar path inclinations, J.A.D.A., 38, 697-710. Friedman, s. (1947) Occlusal harmony in complete artificial dentures, J.A.D.A. , 35, 873-875. UNDBLOM, costa (1949) Term ‘Balanced articulation’, its origin, development and present significance in modern odontology, D. Record, 69, 304-312. Thompson, j. r. (1946) Rest position of the mandible and its significance of dental science, J.A.D.A., 33, 151-180. Bases leader, s. a. (1952) Laminated acrylic dentures, Brit, dent J.. 93, 179-182. osborne, john (1952) The use of self-curing resins in prosthi tic dentistry, Bril. Deni. J., 93, 309-312. (1953) Some observations concerning chrome cobalt denture bases, Brit. Dent. J., 94, 55-67. CleR Palate calk an, j. s. (1953) J. Plastic Surg., 5, 286. FrrzoiBBONS, j. s. (1931) Dental Items of Interest, 53, 737. liddelow, k. p. (1959) Annals Roy . Coll. Surg., 25, 246. malson, t. s. (1957) Non obstructing prosthetic speech aid during growth and ortliodontic treatment, J. Pros. Dent., 7, 403-415. nobistrom, p. h., and anderson, B. d. (1959) Oral Surg., 12, 142. RAMSEY, c. II., WATSON, J. s., el al. (1955) Cinefluorographic analysis of the mechanism of swallowing, J. Radio., 64, 498. rosen, m. s., and bzoch, k. r. (1957 )J. Amer. Dent. Ass., 57, 203. townshend, R. h. (1940) The formation of Passevant’s bar. Jour 11. Laryng. & Otol., 55, 154. WARDILL, w. E. M. (1930) Denial Record, 50, 547. whillis, j. (1930) A note on the muscles of the palate and the Inferior Constrictor, Joum. Anal., 65, 92-95. Dentures fletcher, l. s. (1947) Fundamental principles of full denture construction, D. Survey, 23, 1765-1769- 814 -BIBLIOGRAPHY Matthews, £. {1944) New approach to full denture construction, Brit. Dent. J., 76, 262-268. (*945) Some common causes of failure in dentures, D. Gazette , 11, 258-259. (*942) Stabilisation of lower dentures, D. Gazette, 8, 3i5-3 l6 - TJGHE, j. c. (1949) Construction of full dentures, J.A.D.A., 39, 703-708. Impressions albinson, r. N. (1948) What is mucostatics? D. Survey, 24, 967-970. chick, a. o., and peacock, j. n. (1945) Notes on prosthetic pro- cedures, Brtl. Dent. J., 79, 243-249. ( 1946} Brit. Dent. J., 80 , 23 CHRISTY, R. L. (1943) Impression technique for flabby ridge. Need for surgery eliminated, D. Survey , 19, 44-46. glupker, h. (1942) Complete denture impression materials, their application and manipulation, J.AJO.A., 29, 2216-2220. hurst, w. w. (1946) Importance of a thorough mouth examination as related to the selection of suitable impression methods for edentulous cases, Pennsylvania D. J., 13, 179-187. jorgensen, k. d. (1956) Thiokol as a dental impression material, Acta Odont. Scar'd., 14, 313-334. kile, c. s. (1942) Muscle trimming the hamular notch and soft palate area to get perfect upper impressions, D. Survey, 18, 1632-1634. kinghorx, a., and allen, o. N. (1957) Inlay production from rubber base impressions, Brit. Dent.J., 103, 1-6. knapp, k. w. (1948) H) drocolloid impressions after ten >ears, Nov York D. J., 14, 249-253. mack, a. o (1950) Closed mouth impression technique for full denture construction, Brit. Dent. J., 89, 1 04-105. morange, r. m. (1948} Foumet-Tuller technique for lower dentures, D. Digest, 54, 406-409. pryor, w. j. (1948) Evaluation of several full denture impression techniques, J.A.D.A . , 37, 159-167. skinner, e. w. (1946) Dimensional stability of alginate impression material, J.A.Dui., 33, 1253-1260. spicer, g. it. (1953) Impressions or ridges with hyperplastic tissue, J. Pros. Dent., 3, 163. tomlin, h. r., and osborne, j. ( 1 958) Some observations on silicone impression materials, Bnt. Dent. J., 104, 407-412. BIBLIOGRAPHY S15 TUCKF1ELD, w. j. (1947) Relative importance of impressions in full denture construction, Auslr. D.J., 51, 361-365. (195°) Review of impression techniques in full denture prosthesis, Internal. Dent . J., 1, 1 12. Immediate Dentures ALLEN, a. o. (1952) Immediate dentures, Brit. Dent. J., 92, 212-215. coble, L. g. (1946) Immediate denture technique, D . Surrey, 22, 1870-1873. DAWBORN, r. k, (1948) Immediate denture service, gum faced technique, with partial alveolectomy, Aus. Denial Congress, 11//1 Proceedings , pp. 152-161. Gieler, C. tv. (1947) Immediate denture prostheses, tooth arrange- ment and aesthetics, JJl.D.A., 35, 185-191, KEENEY, B. L. (1948) One day immediate denture service, D. Suney, 24, 1 745-* 747- osborne, john (1945) Immediate restorations, D. Gazette, ix, 300- 3°4- schlosser, r. o. (1946) Rational clinical procedure in complete immediate denture prosthesis, J. South California Dental Ass., *3» *3~*7- (1948} Advantages of conservative procedure in complete immediate denture prosthesis, J. Canadian Dental Ass., 14, 61 1-616, swenson, st. g. (1939) Immediate denture Service, J.A.D.A., 26, 7*9-730- Implant Dentures dahl, c. s. a. (1943) Odontol. Tidsh., 51, 440. MACK, a . O. (1955) Bnt. Dent. J., 99, 287. (1960) Brit. Dent. J 108, 127. TRArNi.Y, b. (1954) Brit. Dent. J., 96, 224. (1954) Bnt. Dent. J., 102, 389. Venable, c. s., stuck, w. o., and beach, a. (1937) Atm . Surg ., 105, 9*7- Mandible chick, A, o. {1949) Forward movement of the mandible during bite closure and its relation to excessive alveolar resorption in edentulous cases, Bril. Dent. J., 87, 243-246. 8 l6 BIBLIOGRAPHY mjrth, l. c. (1949} Physiology of mandibular movements related to prosthodontia. New York D.J., 15, 323-329. (1942) Mandibular movements in mastication, J.A.D.A., 29, 1769--179 0 - Pendleton, E. c. (1942) Minute anatomy of the lower jaw in relation to the denture problem, J.A.D.A., 29, 719-736. Thompson, 3. R., and brodie, a. o. (1942) Factors in the position of the mandible, J.A.D.A., 29, 925-941. Occlusion cason, \v. H. (1947) Securing centric relation, D. Suney, 23, 631-635. holic, r. (1948) Centric registration in full denture construction, J.A.D.A., 36, 296-301. Mcgee, c f. (1947) Use of facial measurements in determining vertical dimension, J.A.D.A. , 35, 342-350. osborne, john (1949) Recording centric occlusion for edentulous cases, D. Record, 69, 6-12. schweitzer, j. w. (1942) Vertical dimension, J.A.D.A., 29, 419-422. sichcr, h. (1948) Temporomandibular articulation in mandibular overclosure, J.A.D.A . , 36, 131-139. Overlay Dentures brill, niels, el at. (1959) Brit. Dent.J., 106, 2. HANKEY, c. t. (1954) Brit. Dent.J., 97, 249. lammie, g. a. el al. (1956) Brit. Dent. J., 100, 33. lindblom, COSTA ( 1 954 ) J- Amer. Dent. Ass., 48, 620. posselt, u. (1959) Dent. Pract., 9, 255. (1959) Paradontologie , 1, 3. REES, l. a. (1954) Brit. Dent. J 96, 125. stCHER, h. (1954) J- Amer. Dent. Ass., 48, 620. WILSON, h. e. (1957) Dent. Pract., 7, 218. Partial Dentures anderson, j. n., and lammie, G. a. (1952) A clinical survey of partial dentures, Bril. Deni. J., 92, 59-67. craddock, f. w. ( 1 946) Labial bar partial denture, New Zealand D.J.,42,6 7. _ Matthews, e. (1952) The partial denture problem, Bnt. Dent . J., 9a, I73-I79- . . , „ (1948) Clasp design in partial dentures, Brit. Dent . J., 85, 152-158. schmidt, A. h. (1947) Partial dentures; planning and designing, J.A.D.A., 35, 562-569. BIBLIOGRAPHY 8,7 smith, e. s. (1949) Importance of evaluating mouth conditions preparatory to the construction of partial dentures, J.A.D.A., 39, 695-702. wait, r>. M., macgregor, A. r., et al. (1958) A preliminary investiga- tion of the support of partial dentures and its relationship to \ertical load. Dent. Pract., 9, 2. Perfecting Occlusion and Articulation coble. L. C. c. (1958) jYcw York Journal oj Dentistry , 28, 306-307. CRADrucK, f. tv. (1949) J.A.D.A., 38, 697. graham, c. H. (1953) The Australian Journal of Dentistry, 59, 100-1 10. KROGH-POU1SEJJ, W. ( 1 958) Internal. D.J., 8, 374-376 li Mir. 1.0 m, c. (1949) Dental Record, 69, 304-31 1 SCflttLER, C. II. (1935) J.ATi.A., 22, II93. siciilr. h. (1956) J.P.D., 6, 616-620. ReIIning aronso.v, h. L. (1942) Simple method of relining metal partial*, D. Digest , 48, 380. chick, a. o., and peacock, j. n. (1946) Relining technique for full upper dentures, Brit. Dent J., 80, 120. craic, tv. e. (1943) Relining an upper denture. Oral Hygiene, 33, 79»-799- . „ levy, clement (1944) Denture rebase with acrylic resin. Cured at mouth temperature, Brit. Dent. J., 76, 305-30G. (1946) Denture relining and acrylic bums, S. Africa D.J., i95-t97* . . osborne, john (1952) Relining and rebasing, Brit. Dent. J., 92, M9-153- Stability Matthews, E. (1942) Stabilisation of lower dentures, D. Gazette, 8 »3«5-3 ,c - RAVBJ.N, N, it, (1949) Analysis of the unstable and ill-fitting artificial denture, J.A.D.A., 39, 177-184. Stomatitis Caiin, l. u. (1919) Denture sore mouth, New York D.J., *5, 158-160. Iieavtnor, R. c. m. {* 913) Acute stomatitis caused by ill-fitting dentures, Brit. Dent. J., 74, 319-320. lyon, d. g., and chick, A. o. (1957) Denture sore mouth and angular cheilitis, Dent. Pract., 7, 212-217. 8 l8 DIBLIOGRAl'IiY Teeth andfuson, h. a. (1047) Functions of the teeth, .l**. /)<•«., 5, >ojj« 107 w \TTlti \v*, r. (iqjo) Tooth placement in full denture construct***, Der.lsl llttotd, 69, *3-17. Tongue I t'ii. r. w. \.tO| 7 . Tnmnte space in full denture construction, PH:. J., 8 j, 137- umia, j. s 1945; Practical full denture prosthesis, l). Iu~i tj IrJrral, 67, 470-478. Index A Absorption: al\ eolar, 14, 366, 399, 435, 574 irregular, 372 rate and degree of, <8 Abutment posts, 795 location of, 789 Acrylic palate, for infant’s cleft, 711, 712 Aerv'ic resin - ad\ images, 337 artificial teeth, for, 255 coIj cure, 396 ccn traction of, 402 di^i chantages, 537 template, 684, 786 Ad in si on, 4, 488, 571 Age, tJie patient’s, 57, 439-444 chronological, 439 ohysiological, 439 Mgmate impressions (see Impressions, alginate) Mginate, sodium . advantages, 168 casting, 142 disadvantages, 168 fixation of, 138 (low of, 140 for edentulous cases, 1 37 impression material, for partial*, 637 combined with composition, 641 internal stresses, 140, 142 method of using, 1 38 setting lime, 140 trays for, 138 Allergy, 6 j, 373 to oil of closes, 144 Allots, metal. cobalt chrome, adi antages, 54 o composition of, 541 disadvantages, 540 mechanical properties of, 541 gold, yellow, advantages, 53“ disadv antages, 539 white, advantages, 539 disadvantages, 539 wrought, advantages, 540 disadvantages, 541 Alveolar absorption, 14, 366, 399, 435, 574 irregular, 372 rate and degree of, 18 Alveolar bone, small spicules of, 64 Alveolar ndges, 16 firmness of, 68 irregularities or, 68 lower, 20 setting teeth in relation to, problem of* shape of. 64 variations, 18 significance of, types of, 19 size of, 64 variations, r8 types of, 1 g upper, 19 Alveolectomy, 79, 411 incision , 79 post -operative procedure, 85 reflection of tissues, 81 removal of bone, 82 suturing, 84 technique of, 79 Anatomical articulation Articulation, anatomical) Anatomy, applied, 7 1 1 Angular chedms, 202, 379 Anterior plane (see Plane, anterior) Anterior teeth I see Teeth, anterior) Anteroposterior compensating curve, 249 Anteroposterior relation, 208 check centric record, for gnnding-in, 350 checking the, 3 1 5 difficulties in obtaining, 208 finished dentures exhibiting incorrect, 3 2 9 in partial denture cases, 648-651 incorrect, as cause of pain, 366 re-taking, 317 relation required for recording, 193, 208-218 Appearance age, 439 chronological, 439 819 &20 INDEX colour change* Sn teeth, due to, 440 gingival contouring for, 443, 444 ■ntcr-demal papilla form in. 443, 444 physiological, 439 teeth, attrition in, 329. 440 position of, 439, 441 selection of, 439 spaces, in, 441 amount of tooth showing, 449 arch form, 449 attrition or anterior teeth, 329, 440 checking, at try 'in, 322, 453 complaint* concerning, 377-382 femininity in, 438 labial and gingival contour, 443. 444 labial flange shape, 447 stippling, 448 masculinity in, 437 position of teeth for, 427 a«je. 439 alveolar absorption, related to, 435 canine, 437 central incisor: facial expression, influence on, 429 factors influencing, sex, 435 personality, 435 irregularity in, 428 lateral incisor, 435 overlapping, 435 rotation, 43(1 selection of teeth for: age. 439 common failings in. 426 mould, central incisor, 427 canine, the, 437 female, for, 419 ovoid, 42 2 lateral incisor. 422 male, for, 419 square, 422 tapenng, 422 personality, by, 419. 42 1 shade, 427 age, bearing on. 427 sue. 423 tn relation to, lip mobility, 423 site of mouth, 424 proportions, 423 snule line, 449 suppling, 448 vertical dimension, facial musculature related to 450. 452 Arch form, 449 related to speech. 308 Articulated models, 2(»! Articulation: anatomical, 26.4-30 1 advantages of, 268 articulator*. 370 balanced, meaning of. 269 defined, 233 faulty. Go factors influencing. 279. 280 incisal angle, 283. 293 lateral movements in, 282 mandibular path, 283-293 effect* of v arijtiort in steepness of, 287 plaster record rim technique, 2118 liases for, 298 rims for, 298 grinding in, 299 recotding j'atv rrf.itiom/ir'ps for, 270 amdyl.tr angle, 271 face Low, 273 mounting models, 277 rotational crtiltrs in, 283, 288 teeth for, 297 cusped, 297 inverletl cusp, 297 plane-line, shortcomings t>f, 264 Artkuhton, 236 anatomical, 370 Artificial dentures (1 ft Dentures, artificial) Asepsis, 77 Atmospheric prrssilre, 6, 488 Attrition of front teeili, 329 B Balance, factors affecting, in anatomical artioilaiion, 279 Balanced, articulation, sfi'l occlusion. 264, 268 Balancing side, 2.y2 occlusion, 292, 293 Jesting for, 322 Bars: burcal, 487 labia), 487 lingual, 4 86 contra-indications fo r » 4^7 palatal, 483 position of. 483 INDEX 821 Base-plates, 179 cold cure acrylic, 180 permanent, 179 acrylic base (heat cured), 181 , cast or swaged metal, 181 swages tin, t8o temporary, 179 thermo-plastic, 180 wax t7q Bennett movement, 52 Bite {see Occlusion) Bite blceks (see Record blocks'! Blood vessels, palatal, 25 exposure of, for implant, 788 impression taking for implant, 788-789 irregularities of, 68 los c *n regions of mandible, 240 nodules, 78 removal of, 85 screws, 802 Border, position of posterior, palatal, 188, 262 Box trays (sec Travs, box) Bndge advantages, 465, 467 definition of. 455 di>ad vantages, 464, 467 Buccal bars {see Bars, buccal) Bulge of Passavani, 730, 732 BULL rule. 336 Burning sensation in the mouth when wearing dentures, 416 C Canine, the, 437 effect of mascuhnitv, 437 position of, 246. 248 Cartes, 575 Cast mrtal strengthener, 398 Casting allovs. 538 white gold, 539 ) elJovv gold, 538 cobalt chrome, 540 Centre line, checking at try-in, 190, 322 Centric occlusion {see Occlusion, centric) Check records for finished dentures, 336- 364 details of procedure, 341-361 face bow, 343 grinding«in: for lateral excursion, 355 for protrusion, 358 in the mouth, 361 perfecting, with gnnding-tn paste, 359 _ reduction of sharp edges, 361 to centric occlusion, 350 to the BULL rule, 356 lateral or protrusive records, 343 mounting in articulator, 345 registration of centric relationship, 34' spot grinding, systematic, reasons fof- 347 partial;, 364 reasons for, 336 articulator wear, 341 incomplete flask closure, 341 incorrect centric occlusion record, 336 ptemature contact and move- ment, 339 irregularities in selling teeth, 340 tooth movement in flasking and packing, 340 set-up in anatomical articulator, 33G plane-line articulator, 361 Cheek biting, 390, 200 Cheek* falling m, 378 Chewing, tnarditular mov ement in mas- tication, 52 Chrome cobalt alloys (see Cobalt chrome alloys) Cingulum resis, 534 Clasp alloys, mechanical properties. 520 Clasps- Mechanical properties or allovs for, 520-524 Classification, 506 Types of encircling, or ocdusally approach- ing, 5 c 6, 507, 51 1 back action form, 314 circumferential form (ring clasp), 5*3 Jackson cnb. 514 one arm form, 512 two arm form . normal arm form, 51 1 recurved aim form, 512 projection, or gingivally approach- ing. 5°7. 5H ball and socket, 5t6 822 INDEX C-shaped, 516 interdental, 517 L-shaped, 515 T-shaped, 514 LF-shapcd, 515 value of, 510 Classification: deft palate, 709 partial dentures, 469-478 patients, 924 teeth, 225, 417-423 Cleaning dentures, 332 Cleft lip (see Lip, deft) Cleft palates (see Palates, deft) Clicking teeth, 200, 387 Closing movement (mandibular), 50 Cobalt chrome alloys: advantages 540 composition of, 541 disadvantages, 540 mechanical properties, 54 c application of, to denture design, 542 Cohesion, 4. 48O (x>lour of teeth (see Teeth, colour o!) Compensating cun cs, 249 anteroposterior. 249 lateral, 251 Complaints. 365-391 altered speech, 390 appearance, 377 cheeks and lips falling in, 3 78 dissamfacuon with, general, 381 teeih, amount showing, 381 colour, 380 position, 380 shape, 380 discomfort, general, 389 clattering teeth, 387 inefficiency* 382 inability to eat, 382 movement when eating, 383 instability, 386 defensive tongue, 387 when eating, 386 when talking, 386 nausea, 388 pain, 365 allergy, 373 cuspal interference, 368 incorrect centric, 3G6 insufficient relief, 366 irregular absorption, 372 mental foramen, 370 monilia albicans, 374 overextension, 363 pathological conditions, 373 poor fit, 36G retained root or tooth, 370 rough demure surface. 374 sharp ridge, 370 sore throat, 376 undercuts, 377 uneven prrwufr, 367 teeth off tile ridge, 369 vertical height ov er dosed, 3 fR over opened, 367 poor retention, 384 when coughing, 3 86 with mouth open, 384 Complete dentures ( see Dentures) Composition: manipulation of, 1 10 thermal conducts ttvaf, i(b tracing stick, J49 (see also Impressions, composition) Composition impressions tsrr Impres- sions, composition) Compression impressions (set Impres- sions, compression) Condylar angle, adjusting the articulator, 2 75 > recording, 271 Condylar path, 271 Condyle: normal position, 41 retrusion of, forced, 698 Connectors, 480 classification of, 480 Consonant sounds, 302, 303, 304 Coronoid process. 133 Cos ten's syndrome, 203 Crossed occlusion (Crossed bite), 260,414 Curves, compensating, 249 of Munson, 251 of Spec, 249 Cusp angles, 287, 2 88 lock. 293 Cuspal interference. 361, 368, 402, 576 dragging action, 3C8 excessive over bite, 369 Cu»prd teeth, 297 inverted, 232, 297 shallow, 232 INDEX O23 D Dakomcter, the, 205 Deafness, 203 Denial arch: preventing collapse of, 457 treatment of contracted, 718 treatment of deformed, ?t 8 v>idi!i of, effect upon speech, 308 Denture base, fracture from fatigue, 12 Denttr- hyperplasia, 88 Denturi lower. 27 po't red lingual surface of, 33 penrmety of, 27 tipi mg forces on, 242 pern ro-lmgual edge of. a6 Dent .re prosthesis, techniques suitable for difficulties encountered in, 408 416 Denture, upper: hack-edge of, 15, 40 periphery of, 33 posterior border of, 262 Dentures: aids to retention, 403-407 appearance of {iee Appearance) artificial, occlusal load on, 42 attitude of patient to, 53 burning sensation when wearing, 416 cleaning, 332 constructed, in adjustable articulator, check records for, 336 in pfane-finr articulator, check records for. 381 reasons for errors found in, 336 difference between natural and arti- ficial, 3 discomfort of, 389 dropping of, 27 easing, 333 technique of, 334 failure of, due to over open vertical height, 44 finished, examination of, 32G check records for (s/c Check records) fitting, full, 32G-335 anatomically articulated, 328 attrition of amrrior teeth, 339 centric occlusion incorrect, 329 checking the occlusion of, 327 instructions to patient, 331-333 far cleft palates [iff Obturators) fracture of, 399 the base, causes of, 399 the teeth, causes of, 402 food under, 391 ill-fitting. 59, 366, 399 instructions to patients, 331 immediate, 662-688 advantages, 688 close occlusion, anterior, 682 copying, appearance when fitting replacement dentures, 686 natural teeth, 6G8 definition of, 6G2 disadvantages of, 688 insertion of, 673 instructions to patients, 676 lower denture. Hanged, G72 trimming model for, 674 partial, 686 prominent premaxilla, G77 refining of, 67G setting up, for, 068 upper denture, root socketing of, 669 damage caused by , 670 with als colectomy , 677-685 reasons for, 677 model trimming for, 683 without als rolcrtomy, 662-667 without prior extraction of posterior teeth, 683-686 implant, 409, 410, 7R5-809 abutment posts, 795 acrylic template for. jR 6 location of, 786, 7O9 balanced articulation for, O07 l tone, screws, 802 impression of, 789 material for, 790, 791 failure or, 808 first oj>e ration for, 788 general remarks concerning. Coll insertion of, 801 laboratory procedure for producing, 7!t3 lower cohalt chrome technique of making 7 86 neutral space, importance of, Hot recording the pm lion of occlusion, 792 shape of dmture for, 709 sulntrurtiire, 7113 internal porosity, 797 super structure. 7118 final lower denture, 8»j 824 INDEX initial lower denture, 799 inefficient}, complaint* of, 382 limitation* of, 3 lower, tipping force* on, jjj mounting in adjustable articulator, 3 15 necessity for, 1 old, existence of, 56 onlay (if* IXmtyrr* overlay) <>\ rrextertsinn of periphery, 5# m erlay , 6119-705 conditions requiting, 669 695 general comrnenti rrificiTiing, 704- orclusal analysis. 701 — ;o| the tem|mro-uandibutar joint, 695- 701 partial* adjusting the occlusion, G53 openeil occlusion cause* of, 653. C’Ji advantage* of, 46 1, 467 assessment of, 454 468 anteroposterior load, resistance to, 564 bases, materials for, 536 513 metal alloys, 538— 543 plastir, 536-538 clis'ificatton, 469-478 l>y occlusal loading, 470 tiwuc-borne, 469. 470 tooili-bome, 469, 470 tnoth'iiswe home, 4 69. 470, 47a Kennedy, 474 modifications in, 478 component parts of, 479*535 eonnectan, 480 buccal and labial bin, 487 plates, 487 lingual, bars, 48G pbin, 483 palatal, bars, 483 plates 483 direct retainers (ire Clasps) indirect retainers f tee Retainers indirect) rests, 530-535 function of, 530 cingulum, 534 1 nasal, 535 occlusal, 530. 53* preparation of tootb for, 53* contra-indications for, 467 damage caused by, 461, 573-576 definition of, 455 design of: basic principles in, 544-617 consideration of loads applied, 544 aniero-posterior, 564-570 dislodging forces. 570-573 lateral, 556-5G4 vertical occlusal, 545-556 tissue health, 573-57G economic factors go' rrning, 576 examples of application of tech- niques, 577-587 Kennedy Class 1, lower, 546, 563. 565. 59'* 593- 597 upper, 558. 567, 595. 599 Class II, lower, 567, Got, G03 L’pper, 555. 567, 577. G05 Class Ilf. loner, 553, 559, 5G4, 607 upper, 547. 55°. 559. C09. Gii.Giz Class JV, upper, G13, 614, GiG. 658 Kennedy bar, 553 material for use in, 536-543 problem* of, 544 retention, consideration of, 579 various examples of. 590-617 disadvantages of, 461, 467 • dislodging forces, resistance 10, 570 fitting finished, 653 settling of, G33, G35 function of, 456 appearance, 457 coilapse of dental arch, 456 masticatory efficiency, 457 immediate, 686 impressions for (j tt Impressions, partial) lateral load, resistance to, 556 line of insertion, 493-498 loads applied to 544*573 methods of flashing, 657 packing through, 657 reverse packing, G57 models for, 647 study, 618, G28 natural teeth, rotation of, 454 position of in relation to treatment of mouth, 618-633 INDEX 825 occlusion, adjusting, G53 opened in, 649. 653, 656 recording of position of, for, 64ft- 651 retention of, 488-489, 496, 506-530, . 57i. 573 direct, 506-525 (see Clasps) indirect 525-530 surveying reasons tor, 489 surveyors, 49a technique of, 492 500 undercut gauges used in, 499 value of, 493 path of insertion from, 493-493 Ussui-bome, 4 6 9-474. 545“55 6 tooth-borne, 469-474, 545-556 rests for, cingulum, 534 incisal, 535 occlusal, 530 preparation for, 530 tooth-tissue borne, 469 470 472, 545 treatment planning clinical examination, 618, 620 history taking, Gt8 study models, 618, 628 X-ray examination, 61 8, 625 try-in for, 651, 652 vertical loading, resistance to, 545 parts of, 235 the base, 235 the teeth, 236 patients attitude to, 55 peripheral outline of, 27 polished surfaces of: lower, 33 upper, 34 poor retention of, 384 when opening mouth, 384 when coughing, 386 posterior palatal border, thickness or, 389 „ . , power loss from closure of the vertical height, .44 previous, effect of, 18 recording the position of occlusion {see Occlusion, centric) reflet control of, 56 ic-hning, 392-398, 676 cold cure acrylic, 396 immediate dentures, 676 impression materials for, 393 reasons for, 392 resilient linings, 397 technique or, 393 repairs to, 398 " singers, for, 416 thickness of, 305 try-in stage, checking of, 309-325 appearance, 322, 323 approval by patient, 323 for balanced articulation, 321 position of occlusion, 315 evenness of pressure in, 319 retaking, 317 the lower denture, 310 occlusal plane, 313 tongue space, 312 cramping, 313 the upper denture, 314 warpage of, 399 wearing at night, 41, 331 continuously, 60 inexperience or, 384 instructions to patient, 33 1 with ‘wings’, 25O Diastema, 44 1 Digital examination, 58, 68 Direct retainers, 488 Discomfort, 389 from increased vertical dimension, 199 Disc', rubber suction, 61, 406 disadvantages, 40G mtracapsular, 48 Displacing forces, 4 instability, causing, 3 Dryness of the mouth, 204 E Easing, dentures, technique of, 334 Eating, 332 dentures dislodged by, 383 inability to eat, 382 Edentulous: the lower, impression area, 95 the upper, impression area, 95 Edentulous state, the, 17C unpleasant, reasons for 2 Elasticity, modulus of, 531 Encircling clasps (see Clasps, types of) Examination: for full dentures, 5-4-75 for partial dentures, 618-633 8s6 INDEX «f finished dentures, 326, 327 ■of trial dentures: full, 309-323 partial, 651, 632 Extraction, under local anxstheiir, for immediate dentures, 676 F Face-bow, 273 Face-bow registration, 273-277, 343 Facial musculature, vertical dimension related to, 450-452 Facial paralysis, 784 Facial prostheses, 772 colouring of, 777 impression for, 772 technique for, 772 Fauces, anterior pillars of, 26 Femininity, in denture appearance, 438 Fenestration, 76O pre-operamc appliance, 768 posi-operam e demure, 769-772 Fibrous ndges, 88 Titling dentures (see Dentures, fitting) Fixed factors, in balanced articulation, methods of measuring patient's, 271 Flabby ndges, 88 Flange, labial, contouring of, 447 in Kennedy Class IV, 569 shape of, 447 Food under denture, 391 Fournct Tuller impression technique, 144 Fosea Palatinae, it, iG Fracture - of denture base, 399 of teeth on denture, 402 Fraena, 27 abnormal, 412 interfering, 87 rraenectomy, technique or, 87 Freewav space, 45, 194 measurement, 195 Full dentures (see Dentures) Functional relation, maxillo-mandibular, 176 FuncUonalfv trimmed periphery (see Impressions, functionally trimmed) G Genial tubercle, 91 Gemoglossus muscle, 92 Gingival contouring of dentures, 443 margin, contour, 444 force of food driven on, 575 relief, 486 trimming, method of, m immediate dentures, G74 Gold alloys: yellow, 538, 539 while, 539. 5G0 Cothic arch tracing, 212, 415 Guide lines, for selling up, 190 centre line, 190 comer lines, 192 high lip fine, 191 Gum-filled teeth, 258 Gum iragacanth, 405 disadvantages, 403 uses, 405 Gutta-percha, 395, 397 11 Hamutar notch, 22 Hamular process, 26 Hard palate (see Palate, hard) History taking, 54 for full dentures, 35 for partial dentures, 618 Horizontal plane, 243-245 Horizontal relationship, 193, 208-318 Humidor, 142 Hyperplasia, 88 granular, 14, 574 Immediate dentures (see Dentures, im- mediate) Implant dentures (see Dentures, implant) Impressions: Alginate, 137, 637, 75° advantages, 168 casting, 142 disadvantages, 168 fixation, 138 flow of, 14° indication for use, 137 internal stresses in, 140, J42 methods of using, 13 3 post damming of, 140 properties of, 137 removal of, 140, 142 setting time of, 14° taking, 137 * « 4 ° JNDtX tray* for, 138 partial, bo*, adapting, 633 bedridden patient*, for, 167 corn posit ion, 15C, 7^ adding to, 115 advantages, 169 cleft palate, for, 749 compression, 156 disadvantages, 169 manipulation of, tto material, for, 103 partial, for, 641 »mi1i alginate. 641 preliminary*, 102 tower, t to common fault* in, its upper, 115 common faults m, 117 wet tonal, G|» tracing, stick, 149 compression (str Impressions, func- tionally trimmed) edentulous patients, for, 91 excessive salivation with, 137 extent of, 94 facial prmiheses for, 722 rovimet, Tullcr. 144 functionally trimmed’ lower, i]} adapting periphery, 410 casting, 154 completing. 154 indications for use, 144 retention tests, 133 special trays for, 141 trimming of. 145-149 u rr rr * *sf> adapting peri pliery, tfu posterior p 1I3t.1I border, 1(13 compression, Ijfi sliffcultics encountered in. 164 retention tests, 163 selection of composition for, 158 •penal tray* for, 159 teel niques for, 159 general it marl.*. 163 inaccurate, denture fracturedue to. 400 lower: preliminary, composition. 1 to common fault* in, 1 12 ridge shallow, 144 working, plaster of Paris, 123 failures of, 13 G materials: edentulous, for. 1 1 8 alginate, 137 composition, 156 composition tracing stick, 14** plaster of Pans, 118 rinc oxidr-rugcnnl paste. 1 43 ideal, tfi ii«l partial*, for. 637 647 alginate, 637 choice of, 645 composition, G41 composition and nlgmatr. '141 synthetic rubber base 63II use of. 640 various, advantages summari/ed, tf) 7 -' 7 ‘ disadvantages sunnnanml, 1(17 » 7 » mucostatic. 645 tausea, control of in. 1O3 partial*, fur. G34 C47 adapting box tray. (*33 choice < f. G37 composiiion f»ji composition and algmiie *>jt matcnal* fur. G37 models from, Gj7 plaster of Pans, 645 seruonal. hji synlhrlic rubber base, G38 plaster of Pan*. 123 advantages, 1G7 l rolrn piece* from, 130 conditioning of, 119 control of, solution for, «i<» disadvantages, 1G7 failure cf, lower, 123 moulding the periphery of, 127 mixing, 1 20 properties of, 1 18 puddling of, 313 removal of. 128, 129 133 lower. 129 upper, 135 setting expansion. 1 1 9 vetting time, 1 19 special plaster*. 1 jn special trays, for. checking « f, 121 828 INDEX pos l damming of. 1 24 technique far. 12*5 upper, 130 moulding (he periphery, 134 position or taking, of operator, 98 of pauent, 98 preliminary, composition, 102 lower, no moulding the periphery, 1 12 common faults in, 1 12 stock trays for. selection of, 103 correction of, 108 taking, reasons for, 102 technique of, no, 1 1 5 upper. 1 15 moulding the periphery, t«6 common faults in, 117 removal ol. 128, jag, 135 retching with, no, u6 ndges, for, shallow, 144 undercut, 137 rubber base, 639 mixing, G39 use of. 640 sectional composition, 641 tracing suck for, 149 travs, partial* for, 634 types of, 102 taking, &4-i7«, <*34-^47 adapting box trays for, 635 difficulty in, due to coronoid process, >33 ideal conditions for. 9 ( nausea experienced, 165 of pamally endentulous mouths, 634-647 order of, 109 peripheral musculature in relation «o, 34 position of operator, 9S patient, 98 trays for, 98 upper, preliminary, composition, 113 common faults in, 117 working, plaster or Paris, 130 failures of, 136 wash, 143 working, 1 18 zinc oxide-eugenol paste, 143 advantages, 168 disadvantages, 169 Incisal rests, 530, S35 function of, 530 Incisive guide table, angle of, 283 setting of. 293 Incisors: anteroposterior position or, 307, 433 attrition of, 440 central, 417, 435 position of. 24G, 248 selection of, 41 7 lateral, 422, 435 position of, 246, 24R rotation of, 43G position of, for speech, 307 selection of mould, 419 for male pa’icnt, 419 for female patient, 419 Indirect retainers («* Retainers, indirect! Inflammation, 12, 58 Interdental papillae, in full dentures, 443, 444 Interference factors, observation of, at examination, 65 Inira capsular disc, 48 Irritation, prosthetic causes of, 58-64 J Jaw relationships abnormal, 414 setting of teeth for, 238 inferior protrusion, 2G0 recording position of in; anatomical articulation, 270 check rrcords for gnnding-in, 341 full dentures, 172 immediate dentures, 66a, 668 overlays 702 partial dentures, 648 superior protrusion, 258 K Kennedy bar, 553 Kennedy classification, 474-478 modifications, 478 designs for (see Dentures, partial design of) Knife-edged ndge (s« Ridge, krofe- edged) L Labial ban ( ue Bars, labial) Labial flange (set Flange, labial) INDEX 829 Labia] plates [see Plates, labial) Labial surface contour (ste Appearance, labial contour} Labials, sounds, 304 Labiodentals sounds, 304 Lateral compensating curses, 251 Lateral excursions, grinding-in for, 355 Lateral loads, resistance to, 556 Lateral movements, anatomical articula- tion, 282 tissue resistance, in partial dentures, 558 Lateral movement, m mandibular move- ment of mastication, 52 Leon Williams' classification, 225-227 ovoid face, 225 square face, 225 tapering lace, 225 Levator veli palatini muscles, 725 Lingual ban (w Kars, lingual) Lingual periphery {set Periphery, lingual) Lingual plates ( see Plates, lingual) Lingual pouch (ste Pouch, lingual) Linguodentals sounds, 304 Lmguopalatais sounds, 304 Linings, resilient, 397, 409 Lip, cleft, 71G splints, 784 Lip, upper, mobility of, 228, 423 Ltps: falling in, 378 tight, 3O3 lower, 413 Loading, resistance to, in partial dentures, antero-posierior, 564-570 lateral, 556-564 occlusal, 545-55 6 dislodging forces, 570-573 Loss of natural teeth 2, 57 Lower ridge ( see Ridge, lower) M Magnets, 407 Mandible, rest position of, Z 73 Mandibular movements, factors influenc- ing, in anatomical articulation, 280 Mandibular movements of mastication, 48753 chewing, 52 closing, 50 opening, 49 shearing, 51 Mandibular path, the, 283 variations in steepness of, 287 Masculinity, 437 Mastication: force applied, 41 muscle of, power of, 41, 44 movements of, 48 Masticatory efficiency, restoration ofi 2, 3. 458 Materials for impressions ( m Impressions, materials) for mating teeth {ste Teeih, materials) Maxillary tuberosities, 71 over-prominent, 86 MaxiIIo-irumdibular relations, 172 Mechanical properties clasp alloys, 520 chrome cobalt, 541 Mental foramen, 370 Metal alloys {set Alloys, m-tal) Metal palates {see Palates, metal Metal plates {see Plates, metal) Models: articulated, 208 mounting m anatomical articulator 27? partiah, for, 64 j study, for, 623 trimming for immediate dentures 683 Modiolus, 28 insertions inio, 46, 452 Modulus of elasticity, 521 Molars, position of: first, 246, 248 second, 246, 248 Moniha albicans- infection with, 374 treatment of, 374 Monson, curve of, 251 Mouth: burning sensation of, 416 dryness of, 204 size of, 424 soreness at comers, 379 surgical preparation of. 76-93 difficulties encountered in, 93 obiect of; 76 Mouthwash, Phenol, 415 Mov c-Ticnt of teeth (see Teeth, movement of) Mucosa, ideal, 69 INDEX 83O Mucostatic impression. 645 Mucous membrane, 12 abnormally thick, 14 assessing health of, G22 colour or, 58 differences in thickness of, 156 flahby areas of, 14 \ ana t ions of, 69 Muscle tone, 45 Muscles' buccinator, 28, 33 bulge of Passat ant, 730, 732 gcnioglassus, 92 1 na.su e 29. 33 levator veil palatini, 725 lips, of the, 46 mastication, of, 41 myh h>oid, 32 obieuhm oru, 29, 34 palato glossvu, 31, 726 palaro phanngeuv, 72G temporalis, 212 tensor sell palatini, 723 sphincter of Whillis, 729, 732 superior constrictor, 31, 726 Muscles of mastication (srr Mastication, muscles of) Muscular control, 571 acquired by denture nearer, 4. 7 Muscular, force, zone of neutral, 239 Muscular potter, 44 Musculature, peripheral, and impression taking. 34 M>Iohvotd muscle, 32 Ms lobs oid ndgrs, 72 N Nasal sounds, 303 Naso-auricular line, 244 Natural teeth ( ste Teeth, natural) N ansa, 40, no, 165 in demure swearers, 388, 415 Neuralgic symptoms, 204 Neutral space, 239, 307, 308, 801 Ncse and chin approximating, 378 Notation of teeth, 454 O Obturators, 718-772 basic horizontal shape of, 735-746 bulge of Passavant, 730 clinical technique for producing, 749 deciding factors in fitting, 746-749 fixed, serving two functions, 731 for intra oral loss of tissue by surgery, 767 for oral fenestrations, 768 for repaired but incompetent soft palates, 752 horizontal plane of location of, 732 impressions for, 749, 350 comprehensive for, 762 post-operative, 768 pre-opera t is e, 768 shaping a speech bulb, 756-762 sphincter of WTullis, 729, 732 laii piece, construction of, 735 locating plane of, 732 try-m of, 75: airaching ssirc loop, 751 treatment for cleft palatrs (s/e Palates clert) t)pes of, 723 Occlusal; analysis, 701, 702-704 plane, j 88, 243, 306, 413 altered, 389 height of, 313 orientation of teeth relative to, 243 pressure, evenness of, 319 restoring, 393 relationships, recording for anatomical articulator, 270. 651 for check records, 341-343 t> pcs of, 253 rests, 530 function of. 530 preparation of tooth for, 531 requirements of, 530 runs, 182 stress-^, checking denture’s stability to, 3«2, 3«4 Occlusion: adjusting the, in partial denture cases, 653 balanced, 264 test for, 32 1 causes of errors in, 336 causing damage to tbsues, indication for overlay, 69 1 centne, 172 difficulties in obtaining, 208 INDEX 83I finished dentures exhibiting in- correct, 329 grinding-in to, 330 incorrect, pain from, 366 antero-posterior relation, 366 over-dosed, sjfifl over-open, 367 uneven pressure, 3C7 maxrilo-mandtbular relations re- lated to, 172 functional relations, 176 required position, 177 rest position, 173 recording the position of- for full dentures, 172-233 amount of tooth showing, 186 anterior plane, 187 antcro- posterior plane, 187 checking record blocks, 1S4 common errors in, 222 horizontal relationship, 193, 208- 318 fatigue, 3li Gothic arch tracing, 212 instruction to patient, «og relaxation, 210 swallowing, 211 temporalis muscle check. 212 longue rctrusion, 209 methods or scaling record blocks, 218 •occlusal plane, 188 posterior palatal border, 1 88, 189 record blocks for, 1 79 guide lines recorded on. centre, 190 comer, 192 high bp, 191 methods of sealing together, 218-222 movement during registration, 339 premature contact of, 339 retention of, fBf trimming, the lower, 193 the upper, 185 the rims of, 182-183 -vertical dimension, 193 effect of over-closure, 200 effect of ov er-opening, 199 free-way space, 194, 195 incorrect, 198 ridge relationship, 198 Willis’s measurement, 197 relations requiring recording, 177 check records for correciing the, in finished dentures, 336-3G4 checking the, 315, 327, 651 classes of faults of, requiring overlavs, 689 close, 414, 623, 628, 682 closure of, 44, 46 correcting by spot-grinding, 347 cross, 260, 414 defined, 235 edge to edge, 261 gauge. Willis, 206 incorrect, as cause of pain, 368 at finish, 329 locked. 293, 361, 573. 691 open, in parual dentures, C53 in processing of, 637 over-closed position of, 200 over-open position of, 199 pre-extraction records, for, 204 articulated models, 208 Da lometer. 203 profile tracings, 207 \\ din’s gauge, 206 recording, for implant dentures. 792 recording the position of, for full deo- dures, 172-223 for partial dentures, 648-631 retaking the position of, 317 squash vvax template record for, 628 technical causes of opened, in partial dentures, 656 technique of registering, 184 tracing devices for centric, 2 12, 213 Occupation of pauent, 58, 416 Onlay dentures (see Dentures, onlav 1 Opening movement in mandibular move- ment of mastication, 49 Operator, position of, 98 Overbitc 49, 253, 288, 294 Over-closed v ertical dimension, pro- longed, 203 Over-erupted teeth, 628 Overextension, peripheral, 385 Overjet, 49, 253, 288, 294 insufficient, 390 Overlapping of anterior teeth, 435 Overlay dentures (see Dentures, overlay) INDEX cuspal interference, 264 reduced efficiency, 264 Plane-line articulator: setting-up teeth on, 235-263 A Plaster, puddling of, 135 Plaster record (bite) rim technique, 298 bases for, 298 rims for, 298 Plaster of Paris, 118-119 advantages, 1G7 an li-ex tansion solution, 119 as iirp.ession material, for full den- tures, 136 for partial dentures, 645 contr >! of, 1 18 disadvantages, >67-168 failures with, in impression taking, 136 impT'S'on technique, lower edentu- lous, 125 partial, 645 upper edentulous, 130 mixing, 120 puddling, 135 setting time of, 1 19 summary- of uses, iGO vigorous spatulation of, effect of, 120 Plasters, special, 120 Plates: labial, 487 lingual, 485 metal. 485 palatal, 483 advantages, 483 damming of, 483 disadvantages, 483 Polymethyl methacylaie (see Acrylic resin) Polyvinyl chloride, 397, 777 colouring of, 777 Porcelain, for artificial teeth, 255 Porosity of implant, internal. X- raying for, 797 Position of I re ih (see Teeth, position of) Post-dam area, 2G2 compression impression of, >63 position or, 188 related to speech, 307 Post-damming, for alginate impression, 140 impression trays, 124 833 Posterior palatal border, pcsin ,n of t^J copving of old demure, a6. thick, 389 Pouch, Ungual, 73 Pre-extraction records (see Record 4 pi« extraction 1 Prcma villa, prominent, 416 677 Premolars . position of first, 2 46, 248 position of second 246 248 Pressure, uneven. 367 correcting', 321 Profile- appearance of. 323 tracing, 207 Projection clasp (see Clasps ’ f pro- jection) Proportional limit, 521 Prosthetics: definition, 1 success in denture, 54 Prostheses: facial, 772, 778 polyvinyl chloride, 777 colouring of, 777 surgical, 767-784 technique, 772 Prosthesis, defined, 1 partial, functions of, 456 Prosthetics, defined, 1 Protrusion, 45 correction of premature ctml.11 ts in, 358 inferior, 260, 414 superior, 258, 414 Ptcry go-mandibular raphe, 1 1 , 2-in, 323 anterior, attrition of, 329. 440 colour of, 229-231, 427, 1 40 complaints concerning, amount \ biUc, 38 1 colour of, 3B0 position of, 380 gum fitted, 238 influencing racial expre-sshm. 429 position of, 323, 427-439, 4 |I related to age, 439-444 shape of, 225-227, 417-422 si/e of, 227-229. 423-426 spacing of. 441 approval by the patient, 323. 453 breakage of, 402 clattering of. complaint oC 387 rn'ouroT, 229-231, 440 bearing of ag? on. 427 cops mg, 668 cuspless, fur shallow ridges, 232, 4,0) faults, 402 fault) arnculanon of. Go function of, 1 ground, reduction of slurp edges of. 3 inserted cusp, 232, 297 materials for making, 255-056 movement of, 349 sshen disking and paekirg. 340 narross. 413 natural, replacement b) artificial, f/») normal arrangement of, 236 notation of, 454 os er-erupled. 628 position of, 236 losscr teeth. 24R relative to one another, 252 upper teeth, 246 positioning of. 427 irregularity in, 42U posterior: form of, 232 selection for anatomical articulato”, 234 .selection for plane line articulator, 232 premature occlusion of, 44, 339, 340 rcgularit) of, position of, 323 relationship of: lower to upper, 252 lower anterior to upper anterior. to plaster models, 237 to the occlusal plane, 2 43 to the ridge, anterior, 307, 429 posterior, 2 jo, 308 10 the vertical *«». 243 selection of, 224-234 classif) ing patimli m, 224 colour, 229 231. 380, 427. 4 jo for male p 3 tient». 419 for female palirtiti, 419 common failings. 4 id shape, 225-227, 380, 417-422 sire, 227-22*1. 423-426 set ling -Op fire .Selting-upl shape, cops jug, G68 sue, length to breadth ratio. 423 surface of: copjmg. 668 jwepa ration of. for rests, 331 uneru ptesf, 370 INDEX "37 upper, set outside ridge, cause of frac- ture, 400 Temporomandibular joint, 41, 48 Bennett movement cf, 52 Cosicn's syndrome, 203 derangement of function of, 695. 699 pain in, 202 Templates, wax, for checking occlusion, 327 , 341 for recording, occlusal position, 219 lateral position. 271, 343 protrusive position, 273, 343 for squash records, 628 Tensor \eh palatini muscles, 725 Th local rubbers, 638 Throat, soreness of, 27, 376 Tinnitus, 203 Tissue- borne dentures (j« Dentures, tissue-borne) Tissues: compressibility sanation in, 156, 412 compression of, J2, 15 inflamed in the mid-line of the palate, 12 presersation of heatih of. 573 ulceration of, 335 Tone, loss of. in the closure of vertical dimension, 46 Tongue, 33 and stability of lower denture. 37 as controlling influence, 7, 38 biting, 300 control of, 240 cramped, 383, 385, 389 causes of, 313 lest for, 313 defensive, 387 functions of, 36 in retching and nausea, 39 in speech, 302 large, 413 movements of in relation to denture design, 37 rest position of. 35 space, 262, 303, 312, 383 Tooth-borne dentures {set Dentures, tooth-borne) Tooth mould, selection of, 225-227, 417- 422 Torus: mandibularis, 90 palaiinuj, it, as, go, 400, 411 surgery for enlarged, 90 Tracing, devices and technique, 213 stick, composition, 149 Trays: box, 634 meihod of adapting. 635 impression, 98 materials for special, 10a methods ofholding, in the mouth, 127- 128 post-damming of, 124 special, for- compression impressions, 159 Toumet Tuller impressions, 144 func(ionod) trimmed impressions, 144 partial impressions, 837 synthetic rubber base, 639 plaster impressions, iai checking and in mining, the lower. 121 the upper, 123 sodium alginate impressions, 138 zinc-oxide eugenol impressions, 143 stock- adapting, 108, C35 faults m, 34 selection of. 105 Traumatic injury, cause of inflammation, 64 Trial dentures (ste Try-in dentures) Tnmming, functional, motion in buccal, 127 labial, 127 lingual, 127 peripheral, 727, 134 Try-in dentures’ 309-325 complete, checking of- lower denture, 310 extension, 311 occlusal plane, 313 penphery, 310 stability, 312 tongue space, 312 upper denture, 314 periphery , 3*4 posterior border, 314 stability, 314 upper and lower together, 315 appearance, 322 balanced articulation, 321 occlusion, 315, 3«9 INDEX 8 3 0 correcting uneven pressure, 331 retaking, 317 \ ertical height, 318 partial, checking ofj 651-653 Tubercles, genial, qt Tuberosities, 1 1, 22, 71, 8C large, 411 Tuller, 1 U Undercut : areas, 7, 85, 137, 489, 496 blocking out. 493 complaints due to, 377 gauges, 499 L nderextension, 311, 383 V V elum rubber. 397 \ ertical axis, 243 orientation of teeth relative to, 343 \ ertical dimension, 44, 193. 306, 450 altered, 389 checking, 318 correcting. 318 e /Teels of, 01 cr closing: appearance, aoa cheek l it mg, 300 Costyn's syndrome, 203 inefficiency aoo pain m the temporo-mundihuhr joint, 202 soreness at the corners of ilie mouth, 202 c/Tects of, over optning - appearancr, 3oo clicking teeth, 200 discomfort, iqg loss of freeway spice, 199 trauma, 199 incorrect, 198 increase of, by re lining, 394 muscle tone, and. 4 5 muscular power, and, 44 prolonged os erclosure of 203 reduced, 390, 410 restoration of by relining. 393 sharp ridges, in cases of, 409 speech, relation lo, 306 Vertical load: examples of, 546 v reducing, 54C Vertical dislodging forces resistance to, 57° Vibrating line, 189 Vowel sounds, 302, 304 Vulcanite, 536 advantages and disadvantages, 537- 53« W Wash impressions, 143 Wax templates, for occlusal position, 327, 31 • for scaling record blocks, 219 for condylar path, 271, 273. 313 squash record, G28 Waxing up, 257 Williams, Leon, 225 Willis* gauge, 206 Will'll’ measurement, ;o 7 White gold alloys {in Alloys. white gnkll Working side, condy Jar movement, 2 ;, 2 Wrought alloys ( ue Alloy*, wrought) X X-ray examination, 74. 618, 625 Y Yellow gold alloys f tee Allow, yellow gold) Z 7 inc oxide-eugrnol paste, 143 allergy to, t4J adsaniagcs, I CO disadvantages, 169 impression, 143 removal of. 141 special I ray for, 143 technique in taking. 143 in cases of nausea, 415 indications for use, i&j