Basic principles in impression making 5
- 1. An analysis of the development of complete denture impression techniques Ira D. Zinner, D. D. S., M. S.D. ,* and Herbert Sherman, D. D. S.** New York University, New York, N.Y. T 1mpression making for complete denture prostho- dontics has matured from the art of carving wooden or ivory blocks that accommodated the intraoral contours to the more sophisticated methods in use today. The various stages are all significant. A historical review demonstrates the advances in techniques which are due to a more thorough knowledge of tissues, their behavior, and their reac- tion to manipulation. While materials used often influenced techniques in the past, material-dictated techniques have long been criticized as have techniques based upon empir- icism. Most materials can be manipulated in almost any way to make impressions. Some materials cannot be used because of physical characteristics which affect tissue reaction, Advances in the theory underlying impression techniques sometimes promote the need for new impression materials. Sometimes the development of a new material permits an accommodation to an improved technique. Despite advances, older tech- niques are continually being used, even though new procedures and theories have been developed. This study documents the frequency and historical development of knowledge associated with scientific advancement from 1845 to 1964 in biology, psychol- ogy, material science, and the clinical sciences as they related to impression procedures in complete prosthodontics. LITERATURE REVIEW A total of 145 books were reviewed from those listed under “Prosthetic Books Published” in the Submitted in partial fulfillment of the requirements for the M.S.D. degree. *Former Associate Clinical Professor, Department of Removable Prosthodontics. **Associate Professor, Department of Removable Prosthodon- tics. 242 SEPTEMBER 1981 VOLUME 46 NUMBER 3 Index of Dental Literature, published annually from 1845-1964. In 77 of these books, there were no references to complete denture impression making. The remaining 68 books were arbitrarily divided by eras for a historical analysis of their relevant con- tent : 1. Prior to 1900-12 books 2. 1900-1929-22 books 3. 1930-1949-18 books 4. 1950-1964-16 books Only textbooks were reviewed and analyzed for this study, since texts are reference books used by the profession. Publications other than textbooks, such as dental journals, were not included. The authors assume that if any important technique or theory of impression making is published in a dental journal, it is eventually published in a textbook. Conversely, it is assumed that impression making techniques or theories that do not contribute or add to existing knowledge do not generally appear in textbooks. When a textbook had a series of editions or revisions, only the latest edition was reviewed. HISTORY OF COMPLETE DENTURE IMPRESSION MAKING Prior to the 1600s complete denture replacements were not made, due to a lack of understanding of retention. Replacements were made only when pos- terior abutment teeth remained in the mouth. Arti- ficial teeth for earlier civilizations were formed of ivory and wood, while a few were mounted on gold plate. Ancient Egyptians, circa 300 BC, wired artifi- cial anterior teeth in the mouth for esthetics. Teeth and bones of cattle as well as ivory were used in making prostheses until the 18th century. The primitive methods of the early 18th century were relatively uncomplicated and used simple materials. In 1711, Matthias Gottfried Purman recorded the use of wax. In 1928, Pierre Fauchard made dentures by measuring the mouth with com- @X2-3913/81/090242 + 08$00.80/O 0 1981 The C. V. Mosby Co.
- 2. DEVELOPMENT OF COMPLETE DENTURE IMPRESSION TECHNIQUES Impression Procedures u. 0 dl ,-dl Comprrsrive oprn Closed Immodiatp Yi Impretrionr Mouth Mouth oenturer 5 ;--II 4 i Era II -1900-1929 Era In-1930-1944 Mucoltctic Relief hole Impressions in tray Fig. 1. Index of frequency for impression procedures. From left to right, first bar graph represents era I-1545 to 1899; era II-1900 to 1929; era III-1930 to 1944; and era IV-1950 to 1964. passes and cutting bone into an approximate shape for the space to be filled. In 1736, Phillip Pfaff of Germany used plaster casts and described a procedure for recording maxil- lomandibular relations. The impressions were made in wax sections of half of the mouth at a time. Plaster of Paris was first used as an impression material in 1844. Credit for its introduction is divided among three dentists-Westcott, Dwinelle, and Dunning. Gutta percha was first introduced in 1848. It was placed in boiling water, kneaded, and molded in the same way as wax and then immedi- ately inserted firmly into the mouth.’ It is of interest to note that some materials presently used were introduced 130 to 250 years ago. 1845-1899 Several basic principles of complete denture impression making were introduced in the middle of the 19th century. The concepts of atmospheric pressure, maximum extension of the denture-bearing area, equal distribution of pressure, and adaptation of the denture-bearing tissues were stressed.‘.” There was an evolution of impression materials which included some types of modeling compound.‘. ’ Many changes in impression making became evi- dent during this era. A single impression, formerly deemed sufficient, advanced to a method using a preliminary impression of gutta percha, beeswax, or modeling compound. This was followed by a second- ary wash impression made of plaster within the preliminary impression.“, ’ Retention, stability, and comfort of the complete denture were described as functions of anatomic considerations in some of the texts in the latter part of this era. Most authors were concerned with stability and retention. There was little discussion in the literature Mandibular Cheek Movement Movement Border Tissue Movemeni Other Oral Tissue Movement 1 Lip Movement Oral Muscle and Tissue Movement Al dl Polatal Pwiphersl Movrment Muscle Mcvamrn t Fig. 2. Index of frequency for muscle and tissue move- ment. regarding tissue behavior and the effects of impres- sion making on tissue. All the impression methods at this time were of an open mouth variety. Closed mouth impression proce- dures were not introduced until well after 1900. Border molding (referred to then as “muscle trim- ming”) varied from pulling the cheeks downward to having the patient himself move the cheeks in a downward direction.“. (i IMPRESSION TRAYS Many types of impression trays were developed during these first formative years. All impression trays (or as they were called “impression cups”) were of metal which was used for durability, strength, rigidity, and lightness. The most commonly used was Britannia metal, but similar alloys or sheet alumi- num permitted trimming and bending to adapt the tray and possessed sufficient rigidity to maintain its shape even under considerable pressure. Other met- als used were lead, copper, tin, silver, German silver, and pewter. Th e impression trays had round or square troughs depending on the material used. Some had high flanges, while others had short. One set of impression trays had double flanges, the upper flange being used to retract the &eeks, lips, and tongue and to prevent them from being caught in the impression, while the lower flange brought the impression material into contact with ridge and contiguous tissue. Another type of tray had an open trough, through which impression plaster was poured so that it would flow throughout the denture- bearing area and into all crevices of the remaining teeth. Nonmetal trays developed during this period were constructed mostly of gutta percha or vulcanite. THE JOURNAL OF PROSTHETIC DENTISTRY 243
- 3. ZINNER AND SHERMAN 1. 6 5I 4- 3- 2- I- o- Pressure Phenomena LkD - Mucostatic Equalization Mosticatory Atmospheric Ion - pressure) of Pressure Pressure Pressure Adhesion n Surface Areo Covoroge Retention Stability Adhesion and Cohesion ? Fig. 3. Index of frequency for pressure phenomena. -c 2l- n DMtur*Extension Anatomic Region Management - __c_ Dirplacrablr Fooiol Ridgoa Contoura Fig. 4. Index of frequency for anatomic concepts. These nonmetal trays were used to make a final wash impression with plaster after a preliminary impres- sion had been made.‘-” 1900-1929 During thte years from 1900 to 1929, there were many innovations in complete denture impression procedures. Reference is still made to the classic textbooks and authors from this era. A concentrated effort was directed toward accura- cy. Most impressions made during this era, as in the preceding one, were of the compressive type. Howev- er, some authors”, i advocated a release or escape vent within the final impression tray to prevent the buildup of excessive pressures. The closed mouth impression Technique was also introduced.* Rebase impressions were mentioned as impressions of a secondary type using a free flowing material which compensated for changes in the tissues. Such final impressions were made within an existing denture or baseplate. Greater attempts were made to understand the need for proper denture extension. Methods of border molding to capture the anatomy of the tissues contiguous to denture borders were introduced. The unique problem of the displaceable maxillary ridge was recognized. Two techniques were developed for handling the “flabby ridge.” The first!’ involved a compressive type of compound impression which displaced the “flabby ridge” palatally. The rationale was that as the patient functioned the denture would move forward, returning the tissues to their normal state. The second method” advocated that hypertro- phied tissue should be captured in its passive form, and a technique was developed accordingly. A number of author? “I described a sucking and swallowing action for border molding in addition to other methods.‘-” Moving the peripheral muscula- ture in the direction of the attachments, resulting in occlusion of the mucobuccal fold both in height and width by the denture borders, was one such method. This is considered biologically sound and within the limits of muscle function. Another method” pro- posed was that of manipulating the musculature against the direction of the muscle fibers, which resulted in foreshortening the final denture borders. The concept, location, and placement of the posterior palatal seal for the complete maxillary denture were explained on an anatomic as well as a mechnical basis. Some authors”. !’ recommended extending the posterior palatal seal ‘/4 inch beyond the vibrating line when the upper anterior tissue was displaceable. One author” advocated ending the 244 SEPTEMBER 1981 VOLUME 46 NUMBER 3
- 4. DEVELOPMENT OF COMPLETE DENTURE IMPRESSION TECHNIQUES O- 7- 6- z J- = 4- s 3- 2-0). l- LLo- 5 I: 30 2- = I- Skeletal - Non specific dlPOlok Tubworitirr Undrrcuir Skeletal - Specific vig? -ii&F -4s -is t Rid99 Notch Palotinur Fig. 5. Index of frequency for bony regions. posterior denture border at the foveae palatini. Most texts, however, report the termination of the posteri- or palatal seal at the vibrating line of the pal- ate,‘. 7-R.11 Acceptance of this concept continues today. Generally, all authors recognized the need for more accurate denture impressions. The most important biologic concept introduced in this era was an awareness of the oral and perioral muscles as they related to the borders of the complete denture impression. For the first time there were references to movement of border tissues and the mandible during impression making. Authors stressed the necessity to determine borders in their most favorable state and further developed closed mouth impression techniques. There was an attempt to relate border and denture-bearing tissues to den- ture function. An increasing number of authors moved from the purely mechanical technique of denture construction to the biologic or biomechani- cal concept. During this second era, no new materials for impression making were introduced, only variants of existing materials. Modeling compound was used as the material of choice for preliminary impressions. The final impression was made in plaster either within the preliminary impression or within a cus- tom tray made of metal, vulcanite, or baseplate. There was increased interest regarding properties and behavior of the materials and their relationship to selected techniques. It was during this era that the concept of esthetics’ in impression making was introduced. 1930-1940 This era recognized the anatomy of the denture- bearing areas, and of muscle physiology as related to impression procedures. dill Tongue MUSCI~Attachmmts Muscles - Non-specific r-7 dCheeks 5 (Frrno) Muscles - SDecif ic Mylohyoid Buccinotor r- MWCIO Morlctsr MUSCIO Superwx Mu~cla Constrictor Muscle Fig. 6. Index of frequency for muscles. G Chemoplar t ic-7 Zinc Osidr C Matrrlolr Polymer-- Type--- Materials 3- 4- 3- 2- Thermoplaetic-- MoterloC Colloidal Materials I1 -41Alginotr Hydrocolloid Trays-- Fig. 7. Index of frequency on thermoplastic materials. There was greater knowledge of muscle anatomy and muscle physiology and the effects of the muscu- lature upon dentures. This is evident in descriptions of border molding of dentures. Many authors’3-“1 advocated manipulation in border molding by mov- ing the peripheral musculature in the direction of its fibers rather than against this direction. The need to completely cover the retromolar pad for maximum stability was stressed.‘J-“’ Additionally, there was emphasis on immediate denture impression techniques.‘“. 2*-2y‘the only prior reference regarding immediate denture impressions THE JOURNAL OF PROSTHETIC DENTISTRY 245
- 5. ZINNER AND SHERMAN and Atrophy Resorption Trauma, etc. Strotiticd Squamous Epithelium Connective Tissue Histologic References Fig. 8. Index of frequency for pathology and histology. was Litch (1887). Immediate dentures were used not only for esthetics but for maintenance of muscle tonicity, in the perioral musculature. Several new impression materials were intro- duced: reversible hydrocolloids, zinc oxide-eugenol, and zinc oxide and oil of cloves.” Modeling com- pound and plaster still remained the two major impression materials used in both preliminary and final impression procedures. There was a greater understanding of the properties and behavior of modeling compound and plaster,“. ‘li some under- standing of the properties of the zinc oxide-oil of cloves impression paste,” and very little understand- ing of the properties of the hydrocolloids.“’ In the 193Os, most techniques stressed the use of plaster for fina’l impression procedures. In addition, there was a trend away from making the final impression ti<thin the preliminary compound impression. Construction of an individual tray from a cast of the preliminary impression was emphasized, and the final impression was made in this individual or customized ‘tray. The value of mandibular posture records and their relationship to the impression procedure was recognized. A few authors” advo- cated using a closed mouth impression procedure at the correct vertical dimension of occlusion in centric relation. There was a trend against displacement of the hypertrophied maxillary anterior tissue palatally. Emphasis was placed more upon making impressions of displaceable tissue in its passive state.‘“. “. ” The introduction of a new impression procedure and the concept of mucostatics occurred in this era. The idea was to achieve the best possible adaptation of impression material to tissues and to capture the tissues in their passive undistorted form. r Coughing LO- ‘;; :: m = OS- d Patient Comtor t Vomiting. Smd I, Nall**a Taste 1 Phvsiolog& References Psvcholoaic. References Patient Desire, Hobits. Instruction Fear, etc. Fig. 9. The index of frequency on physiology and psy- chology. 1950-1964 In the period from 1950 to 1964, there was increased emphasis on those biologic factors that affect complete denture impression making. Clinical procedures advocated earlier were described with greater insight into the anatomy and physiology of the oral and perioral tissues. Awareness of muscle movement and relationship to complete denture impressions was evident. Most authorSlX, “3. 24 advocated the use of one or more escape vents in the individually constructed impres- sion tray prior to making the secondary or final impression. There was greater emphasis on flanges, border molding, and denture extensions. An increase of interest in the posterior palatal seal was obvious as was emphasis on the management of the displace- able ridge. There was also more attention given to the relationship of esthetics to complete denture impression techniques. Despite these advances, modeling compound remained the material of choice for making prelimi- nary impressions. Secondary impressions were described as being made with zinc oxide-eugenol paste or plaster. Other types of impression materiaWJ such as rubber base (mercaptan or thiokol) and silicones were introduced. More authors’“, “‘I. ?“. “’ advocated the use of an individually constructed nonmetallic tray to be used for making the final impression wash, rather than making it inside the preliminary com- pound impression. There was a greater understanding of the proper- ties of the various materials used in complete denture 246 SEPTEMBER 1981 VOLUME 46 NUMBER 3
- 6. DEVELOPMENT OF COMPLETE DENTURE IMPRESSION TECHNIQUES Table I. Number of references and index of frequency by eras 12 books 22 books 18books 1845-1899 1900-1929 1930-1949 Clinical techniques No. of references and index of frequency 16 books 1950-1%4 Impression procedures Compressive Open mouth Closed mouth Immediate denture Mucostatic (nonpressure) Relief hole in tray Rebase Vibrating line Modiolus Fauces Junction of hard and soft palate Labial muscles Muscles of mastication Lingual muscles Specific muscular areas Mylohyoid Buccinator Masseter Superior constrictor Orbicularis oris Geniohyoglossus Palatoglossus Temporal Internal pterygoid Mentalis Incisivus inferioris Caninus Geniohyoid sty10g10ssus Buccal shelf Coronoid process Genial tubercle Premylohyoid eminence Retromylohyoid eminence Mental foramen Posterior palatine foramen Anterior palatine foramen Torus mandibularis Canine fossa Palatine groove Incisive fossa Incisive foramen Nonspecific muscular areas Lips Tongue Muscle attachments (Frena) Cheeks Muscles of facial expression Peripheral muscles Floor of mouth Soft palate 29 2.42 31 2.58 - - 2 0.17 - - - - 2 - - - 0.17 - - - - - - - - - - - - - - - - - - - - - - - - - - 13 1.08 10 0.83 5 0.42 13 1.08 1 0.08 8 0.67 73 48 25 3.31 2.18 1.14 - 2 0.09 45 2.05 5 0.23 1 0.05 2 0.09 5 0.23 6 0.27 2 0.09 4 0.18 80 4.44 61 3.39 31 1.72 9 0.5 1 0.06 12 0.67 22 1.22 2 0.11 - 1 10 0.06 0.56 112 7 105 6.56 32 2 19 1.19 18 1.13 17 1.06 15 0.94 11 0.69 10 0.63 6 0.38 5 0.31 3 0.17 1 0.06 - - - - 0.41 0.64 0.45 - 0.09 0.05 - - 12 0.67 16 0.89 3 0.17 1 0.06 10 0.56 1 0.06 6 0.33 - - - - - - - - 1 - - - 5 - - - - - 1 0.06 - - 0.05 - - 1 0.06 1 0.06 6 0.33 0.23 17 1.06 16 1 10 0.63 10 0.63 9 0.56 7 0.44 6 0.38 4 0.25 3 0.19 2 0.13 2 0.13 2 0.13 2 0.13 2 0.13 3 0.19 3 0.19 3 0.19 3 0.19 2 0.13 2 0.13 2 0.13 2 0.13 2 0.09 6 0.33 7 0.39 6 0.33 3 0.17 2 0.11 1 0.06 4 0.22 1 0.06 - - - 49 2.23 69 3.83 117 7.31 29 1.32 43 2.39 103 6.44 70 3.18 74 4.11 102 6.38 45 2.05 37 2.06 83 5.19 3 0.14 6 0.33 48 3 35 1.59 31 1.72 29 1.81 16 0.73 17 0.94 25 1.56 21 0.95 10 0.56 22 1.38 THE JOURNAL OF PROSTHETIC DENTISTRY 247
- 7. impressions, including plaster, modeling compound, and the materials used for impression trays. The properties of zinc oxide-eugenol impression paste and how the pa!jte related to tissue were better understood than when first introduced. despite the introduction of new materials such as zinc oxide-eugenol paste, alginates, reversible hydro- colloids, thiokol rubbers, and silicones (Fig. 7). SUMMARY There were very few references to pathology, histalogy, and behavioral aspects of impression mak- ing and no trend was observed over the four eras (Figs. 8 and 9). Sixty-eight textbooks published in English since 1845 have contained references to impression mak- ing. References in these volumes to biologic, psycho- logic, behavioral and material science, and to clinical procedures were recorded. These notations were then tabulated into four eras for statistical analysis. The history of impression making shows that most of the significant advances occurred before 1930. Basic principles of pressure, maximum extension of the denture base over the denture-bearing area, and equal distribution of pressure were first introduced in the era 1845 to 1899. There were a total of 9,005 references in the various categories. For each classification an index of frequency was calculated (Figs. 1 to 9). The index of frequency is the number of times an item was recorded in an era divided by the number of books in that era. For exa.mple, under the category of pressure phenomena (Fig. 3), a reference to “equalization of pressure” in the 1900 to 1929 era was recorded 33 times. There were a total of 22 books published in this era. Therefore the index of frequency for this item in the second era is 33 + 22 or I .5 (Fig. 3). The index of frequency gives a measure of the interest in impression making (Table I). The most significant advances in the art were developed in the second era, 1900 to 1929. Advances in the accuracy of impression techniques and an increase in the methods of border molding and obtaining a posterior palatal seal were among the major innovations in this era. The era from 1930 to 1949 saw great advances in the knowledge of the anatomy of the oral and perioral tissues as they affect impression making. The use of immediate denture techniques and the introduction of several new materials such as zinc oxide-eugenol paste and the hydrocolloids were also noted. An increase in the index of frequency for compres- sive impressions, border molding, and denture exten- sion was recorded over four eras. References to closed mouth impressions showed a smaller increase. No increase in references to displaceable ridges and facial contours was seen over the four eras, and a decrease was noted in the index of frequency for rebase impressions (Fig. 1). The fourth era saw progress in the biologic aspects of denture impression making. There was an appre- ciation of the rationale for border molding and an awareness of the muscles and how they relate to complete denture impression techniques. The index of frequency increased greatly in vari- ous categories of oral muscle and tissue movements over the four eras as authors became more sophisti- cated in the biologic concepts of impression making (Fig. 2). Simil,arly there were large increases in the index of frequency for many subcategories of physi- cal phenomena-surface area coverage, retention, denture extension, and soft tissue displacement (Fig. 3). On the orher hand, references to atmospheric pressure, peripheral seal, posterior palatal displace- ment, and border tissue adaptation showed little or no trends over the four periods of time. The importance of an in-depth review of impres- sion making lies in the assessment of the historical value of all factors. The categorization for these factors into their respective physical, biologic, and behavioral areas can show their relativity to the time in which they were discussed and taught as well as to their assigned importance. REFERENCES Index of frequency for references to anatomic areas remained fairly constant for nonspecific sites but showed an increase in references to specific bones, muscles, and oral spaces (Figs. 4 to 6). References to modeling compound and plaster showed large increases, especially in the later era, 1. 2. 3. 4. 5. Prothero, J. H.: Prosthetic Dentistry. Chicago, 1916, Medi- co-Dental Publishing Co.; ed 3, London, 1921, Charles Ash and Sons, chaps 5-7, and 25. Harris, C. A.: The Principles and Practice of Dental Surgery, ed 2, part 6. Philadelphia, 1845, Lindsay & Blakiston, chaps 2 and 4. White, J. W.: Taking Impressions of the Mouth, ed 2. Philadelphia, 1895, S. S. White Dental Mfg. Co. Essig, C. J.: The American Textbook of Prosthetic Dentistry. Philadelphia, 1896, Henry Kimpton, chap 6; ed 2, New York, 1900, Lea Brothers and Co. Richardson, J. A.: Practical Treatise on Mechanical Dentist- ry. Philadelphia, 1860, Lindsay & Blakiston, chap 2; ed 2, 1868; ed 3, St. Louis, 1880, Hildreth Printing Co.; ed 4, 248 SEPTEMBER 1981 VOLUME 46 NUMBER 3 ZINNER AND SHERMAN
- 8. DEVELOPMENT OF COMPLETE DENTURE IMPRESSION TECHNIQUES 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. London, 1886, J. & A. Churchill Ltd.; ed 6, 1893, revised and enlarged by George W. Warren; ed 7, London, 1903, J. & A. Churchill Ltd., chaps 13 and 14. Turner, C. R.: The American Textbook of Prosthetic Den- tistv. Philadelphia, Lea Brothers and Co.; ed 2, London. Henry Kimpton; ed 3, 1907, revised and rewritten; ed 4, Glasgow, 1913; ed 5, Turner, C. R., and Anthony, L. P., editors, London, 1928, Henry Kimpton; ed 6, Philadelphia, 1932. Lea & Febiger, chaps 3 and 14. Campbell, D. D.: Full Denture Prosthesis. St. Louis. 1924, The C. V. Mosby Co., chaps 1, 4, 7, and 16. Lieberthal, R. H.: Advanced Impression Taking, New York, 1919, Professional Publishing Co.. chaps 1 and 2. Greene, J. W.: Greene Brothers’ Clinical Course in Dental Prosthesis. In three printed lectures: 1910, 1914, 1916. Detroit, Detroit Dental Mfg. Co., lectures 1 and 2. Clapp, G. W.: The Mechanical Side of Anatomical Articu- lation. New York, 1912. Dental Digest Press. Wilson, G. H.: A Manual of Dental Prosthesis. New York, 1917, Lea and Febiger; ed 2, London, 1914, Henry Kimpton, chap 2; ed 3. 1916, ed 4, 1920. Bunce, E. W.. The Bunce-Kanouse Full Denture Technic. Chicago, 1929, Coe Laboratories, Inc., Chapters 3-5. Nichols, I. G.: Prosthetic Dentistry. An Encyclopedia of Full and Partial Denture Prosthesis. St. Louis, 1930, The C. V. Mosby Co., chaps 4, 14, and 30. Neil, E.: Full Denture Practice. Nashville, 1932, Marshall & Bruce Co., chaps 3-5. Fish, E. W.: Principles of Full Denture Prosthesis. London, 1933, John Bale Sons & Danielsson; ed 3, London, 1937, John Bale & Sons and Curnow; ed 4, London, 1948, Stapler Press; ed 5, London, 1952, Stapler Press; ed 6 (Appendexes contributed by Ernest Matthews), London 1954. Stapler Press, chap 4, Appendexes 1, 2, and 4. 16. 17. 18. 19. 20. 21. 22. 23. 24. Litch, W. F.: The American System of Dentistry, vol 2-Operative and Prosthetic Dentistry. Philadelphia, 1887, Lea Brothers & Co., part II, chap 1. Doxtater, L. W.: Full and Partial Denture Prosthesis. Brook- lyn, 1936, Dental Items of Interest Publishing Co.; chaps 2, 13, 16, and 21-23. Craddock, F. W.: Prosthetic Dentistry: A Clinical Outline, ed 2. London, 1951, Henry Kimpton, 1945, chapter 3. Schlosser, R. 0.: Complete Denture .Prosthesis, ed 2. Phila- delphia, 1939, W. B. Saunders Co.; ed 2, 1946; ed 3, 1953: ed 4, Gehl, D. J. and Dresen, 0. M., editors, 1958, chapters 6, S-11, 21, and 22. Swenson, M. G.: Complete Dentures St. Louis, 1940, The C. V. Mosby Co.; ed 2, 1947; ed 3, 1953; ed 4 (in collaboration with Stout, C. J.), 1959; ed 5, 1964, Boucher, C. O., editor, chaps 3, 13, 19, 31-33, and appendix. Sears, V. H.: Prosthetic Papers. Minneapolis, 1936, Dental Library, Bureau of Engraving, Inc. Boyle, H. H.: The Principles and Pracice of Applied Dental Aesthetics. London, 1936, Henry Kimpton, chaps 3 and 13. Landa, J. S.: Practical Full Denture Prosthesis. London, 1947; Brooklyn, 1954, Dental Items of Interest Publishing Co.; London, 1958, Henry Kimpton, chaps 8-10, 31, and 32. Lammie, G. A.: Full Dentures. Oxford, 1956, Blackwell, chaps 4 and 5. Reprint requeststo: DR. IRA D. ZINNER 115 E. 61s~ ST. NEW YORK, NY 10021 THE JOURNAL OF PROSTHETIC DENTISTRY 249