FPD Design

CLASSIC ARTICLE Current theories of crown contour, margin placement, and pontic design Curtis M. Becker, DDS, MSD,a and Wayne B. Kaldahl, DDSb University of Colorado, School of Dentistry, Denver, Colo, and University of Nebraska, School of Dentistry, Lincoln, Neb

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ne of the prime goals of restorative therapy is to establish a physiologic periodontal climate and facilitate the maintenance of periodontal health. Crown contour, margin placement, and pontic design all affect periodontal health. This article reviews the current theories of all three of these.

CROWN CONTOUR The contours for full and partial coverage restorations play a supportive role in establishing a favorable periodontal climate. Three prominent theories of crown contour have evolved: (1) ginvial protection, (2) muscle actions, and (3) access for oral hygiene.

Gingival protection theory The gingival protection theory advocates that contours of cast restorations be designed to protect the marginal gingiva from mechanical injury (Fig. 1). The concept of protecting the gingiva has been with dentistry for many years.1,2 A number of dental anatomy textbooks,3,4 periodontal textbooks,5,6 and respected clinicians1,7,8 advocate the concept of gingival protection with little or no supporting scientific evidence. Statements in support of gingival protection appear to be primarily empirical. Wheeler9 has stated, ‘‘The gingiva is apt to be stripped or pushed apically through lack of protection and consequent overstimulation.’’ The axiom of gingival protection has become so ingrained in the dental literature and teaching that for years this concept was seldom challenged. Some dentists and laboratory personnel apparently have reasoned that, if a little gingival protection is good, then more is better. This theory and the increased use of full coverage veneer crowns have produced an era of overcontoured restorations. Wheeler9 has remarked that, when molars have curvatures in excess of normal, the gingiva will be overprotected and will suffer from lack of proper stimulation. Wheeler’s warning was based on ‘‘protection’’ of the gingiva. a

Clinical Assistant Professor, Department of Restorative Dentistry, University of Colorado, School of Dentistry. b Assistant Professor, Department of Periodontics, University of Nebraska, School of Dentistry. Reprinted with permission from J Prosthet Dent 1981;45:268-77. J Prosthet Dent 2005;93:107-15.

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Fig. 1. Double deflecting contours have been advocated by some authors, allegedly to protect the marginal gingiva from mechanical injury.

The gingival protection theory has been defended primarily on the basis of three elements: protection of gingival margins, gingival stimulation, and self-cleansing contours.10 Protection of gingival margins. This concept implies that undercontouring of the clinical crown will cause deflection of masticated food onto the gingival margin, forcing it into the sulcus, thus initiating gingivitis. This concept may have originated from the observation that interproximal food impaction occasionally can initiate acute inflammation. However, numerous studies have demonstrated a cause-and-effect relationship between plaque and gingivitis,11-13 and in comparison, the interrelationship of periodontal disease and food impaction appears slight. Many authors14-17 have THE JOURNAL OF PROSTHETIC DENTISTRY 107

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Fig. 2. The temporary crown on this molar has been missing for 8 weeks; in spite of the obvious lack of contour, there is no evidence of marginal inflammation, food impaction, or gingival stripping.

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Fig. 3. The evidence of plaque accumulation at the gingival one third of this patient’s teeth emphasizes that self-cleansing contours in this area are nonexistent, regardless of diet.

Fig. 4. Buccal and lingual contours of full and partial coverage cast restorations should be kept flat to facilitate plaque control and maintain gingival health.

Fig. 5. The embrasure space with restorations such as these maxillary crowns should be kept open to allow access to the interproximal spaces for plaque control and for natural architecture of the interdental papilla.

reported situations where crowns or temporary fixed partial dentures have been lost or removed for long periods of time with no apparent ill effects to the surrounding gingiva (Fig. 2). Schluger et al18 stated, in discussing crown contours, ‘‘the so-called protective cervical bulge that hypothetically protects the human gingival crevice protects nothing but the microbial plaque.’’ Koivumaa and Wennstrom19 studied the histologic effects of crown contour on human gingiva. They found that there was an increase in inflammation adjacent to bulbous artificial crowns but that properly contoured artificial crowns exhibited no such increase at the adjacent gingiva. Perel,20 in studying dogs, cut Class V preparations 0.5 mm above the buccogingival crest. He then overcontoured some restorations and undercontoured other

restorations. After 9 weeks, he found no clinical or histologic changes with the undercontoured restorations; but with the overcontoured restorations, he reported evidence of inflammation and hyperplasia both clinically and histologically. Thus, there appears to be no evidence to support crown contours designed to ‘‘protect the gingival margins.’’ Gingival stimulation. This concept reasons that, as food is masticated, it will pass over the gingiva, stimulating it and causing increased keratinization of the epithelium. The keratinized epithelium would be more resistant to periodontal breakdown. Several authors21-24 have shown that the gingival margin is not in the path of masticated food. Even if the food passing over the teeth were to increase keratinization (there is little evidence to back this assumption),

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Fig. 6. Contacts between restored teeth should be kept at the incisal one third of the tooth to facilitate an accessible embrasure space. The anatomy from the contact area to the margin of the restoration should be flat or concave (never convex).

this stimulation would only occur at the buccal and lingual surfaces, leaving the interproximal tissues without proper stimulation. It appears that, under normal circumstances, the mechanics of mastication has very little effect on gingival health. Self-cleansing contours. This concept asserts that, as food passes over the tooth during mastication, the tooth will be cleansed. While certain prominent buccal and lingual surfaces of teeth do not accumulate plaque even in neglected mouths, numerous authors21,22,24 have shown that mastication does not remove plaque at the gingival margins of teeth. Neither does mastication have any effect on the progress of gingivitis.22 Thus, self-cleansing crown contours apparently are nonexistent at the gingival margins of the teeth (Fig. 3).

Muscle action theory Morris15,16 was one of the first to question the rationale of the gingival protection theory. He and others25-28 have suggested that overcontouring prevents the normal cleansing action of the musculature and allows food to stagnate in the overprotected sulcus. Lindhe and Wicen,22 Loe,11 and others29 have all demonstrated that, in the absence of oral hygiene, ‘‘self-cleansing’’ mechanisms do nothing to prevent gingivitis. Even if there were some cleansing of the buccal and lingual surfaces from muscle action, interpoximal cleansing still would be impossible. Some proponents of the gingival protection theory also concur with the muscle action theory.5,6,14,27,28 These authors strive for an intermediate design of crown contour which allows for both gingival protection and muscular action. FEBRUARY 2005

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Fig. 7. Contacts (C) between natural teeth are buccal to the central fossa (CF) except between molars. This allows space for the relatively large lingual papilla (P).

Theory of access for oral hygiene This theory is based on the concept that plaque is the prime etiologic factor in caries30-32 and gingivitis.11,29,33 Thus crown contour should facilitate plaque removal, not hinder it.18 When crowns were overcontoured experimentally, 64.3% of the test sites demonstrated an increase in periodontal inflammation. This was attributed to decreased access for oral hygiene.34 The four guidelines to contouring crowns with emphasis on access for oral hygiene will be described. Buccal and lingual contours–flat, not fat! (Fig. 4). Numerous authors17,18,21,25 have demonstrated that plaque retention on the buccal and lingual surfaces occurs primarily at the infrabulge of the tooth. Reduction or elimination of the infrabulge would reduce plaque retention.18 Perel20 demonstrated that in actuality undercontouring may promote gingival health. Ramfjord,35 Yuodelis et al,17 and an increasing number of other authors have come to the realization that overcontouring is a greater periodontal hazard than undercontouring. The normal buccolingual contour of teeth without caries is quite flat. Most authors who have studied normal tooth contours2-4,9,36,37 have reported that rarely is the buccolingual width of these teeth more than 1 mm wider than the cementoenamel junction (CEJ). Thus, a normal tooth at the buccocervical bulge is usually # 0.5 mm wider than the CEJ. Open embrasures. If plaque is a primary etiologic factor in gingivitis,18,33,38 then every effort should be made to allow easy access to the interproximal area for plaque control.18,35,39 Open embrasure spaces will allow for this easy access (Fig. 5). An overcontoured embrasure will reduce the space intended for the gingival papilla. The result is a broadening of the col area, causing pressure and irritation on the papilla. This also 109

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Fig. 9. A cast restoration which flutes into the furcation of a periodontally involved molar (A) can effectively reduce the triangular ‘‘plaque trap’’ region that results from restoring the original anatomy of the crown (B).

Fig. 8. Furcations should be ‘‘beveled’’ from the margin of the restoration to the occlusal surface. This reduces plaque traps created by the anatomy of the furcation region and facilitates plaque control. A, Mandibular crown contour of buccal furcation. B, Maxillary crown contours of lingual furcations.

inhibits effective oral hygiene.40,41 Several authors35,36,42-46 have suggested or implied that an interproximal space that is slightly larger than normal may be desirable since it provides adequate room for the gingival papilla and is a more accessible area to clean. Some authors5,42,43,47 have reported the fear of creating an environment which promotes ‘‘lateral food impaction’’ when open embrasures are employed. Townsend48 has observed that, even with grossly undercontoured, open embrasure spaces, lateral food impaction rarely occurs as long as interproximal tooth contacts are properly maintained. Several authors49-51 have demonstrated that the most effective method of interproximal plaque control in gingival recession is the use of an interproximal brush. When the interproximal brush is used, the space between two adjacent proximal surfaces must be wide enough to allow it to pass through with relative ease. Location of contact areas. Contacts should be high (directed incisally) (Fig. 6) and buccal in relation to the 110

central fossa (except between maxillary first and second molars) (Fig. 7). Several authors3,36,52,53 have demonstrated that the contact areas on natural teeth occur at the incisal one third of the tooth. Many agree that natural teeth are straight or slightly concave interproximally from the CEJ to the contact area.1,3,4,18 This tends to open the embrasure, particularly if the contact area is high (in the incisal direction). Many authors36,37,43,44,53 have pointed out that the contact area of all teeth, except between the maxillary first and second molars, should be buccal to the central fossa. This creates a large lingual embrasure for optimum health of the lingual papilla. Hazen and Osborne45 have warned of the consequences of an ‘‘oversized’’ col resulting from broad (buccolingual) contacts. The col is a nonkeratinized area which is thought to be more susceptible to plaque. The broad contact produces a larger col, thereby leading to increased chance of inflammation. Ramfjord35 recommends placement of contact areas as far occlusally as possible to facilitate access for interproximal plaque control. Furcations involvement. Furcations that have been exposed owing to loss of periodontal attachment should be ‘‘fluted’’ or ‘‘barreled out’’ (Fig. 8). The concept of fluting into molar furcations is based on the desire to eliminate ‘‘plaque traps’’ and facilitate plaque control.18 Yuodelis et al,17 in discussing molar furcations, warn that the final restoration should not follow the anatomy of the original clinical crown but should be an extension of the contours of the periodontally exposed roots. When this approach is properly executed, the triangular VOLUME 93 NUMBER 2

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Fig. 10. Supragingival margins generally provide a more favorable environment to resist disease than subgingival margins.

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Fig. 11. Ridge-lap pontics can create gingival inflammation, bleeding, and severe discomfort.

Fig. 12. A, Diagram of modified ridge-lap pontic design for posterior teeth. Note that the pontic does not contact the tissues lingual to the crest of the ridge. B, The modified ridge-lap pontic (first molar). Note the open embrasures, minimal tissue contact, and gingival health.

region that is created by the roots and the cervicular bulge is eliminated (Fig. 9). This triangular region is the most difficult area to maintain in a plaque-free condition with conventional brushing techniques. We have found that by recontouring the furcation to eliminate the triangle, plaque control with normal brushing is greatly facilitated (Fig. 8).

MARGIN PLACEMENT The concept of subgingival margins is a natural outgrowth of G. V. Black’s54 ‘‘extension for prevention’’ and the ‘‘caries-free zone.’’ Locations for marginal placement for cast restorations have included: (1) the base of the gingival crevice55; (2) half the distance between the base of the gingival crevice and the gingival margin56; (3) slightly below the gingival margin25,41; (4) the crest of the gingival margin57; and (5) supragingivally.14,18,58,59 With each of these margin locations, the authors have reported clinically healthy periodontal FEBRUARY 2005

tissues when quality restorations were combined with effective plaque control. As early as 1941, Orban60 proposed supragingival margins for improved periodontal health. Orban60 and other researchers61,62 discovered that the ‘‘caries-free’’ or ‘‘clean’’ subgingival zone, which had been observed previously on extracted teeth, was nothing more than the location of the epithelial attachment. This epithelial attachment will not attach to the margin of a cast restoration. Thus the concept of routine subgingival margins was questioned as more scientific evidence appeared (Fig. 10). Plaque accumulation, inflammation, and gingivitis are reported to occur more frequently in teeth with subgingival crown margins than in those with supragingival margins.18,57,59,63-69 Oral hygiene instructions do not seem to alter this pattern.23,66,70 Few incidences of new caries associated with supragingival margins have been reported because of improved access for plaque control.69 Christensen71 has 111

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Fig. 13. A, Diagram of ridge-lap facing pontic design for anterior teeth. Note that the pontic does not contact the tissue lingual to the crest of the ridge. B, The ridge-lap facing pontic (left lateral). Note the open embrasures, minimal tissue contact, and gingival health.

Fig. 14. The cusp tip-to-cusp tip width of a posterior pontic (P) should be the same width as the original missing tooth.

demonstrated that the visually accessible margin (supragingival) can be, and is, fitted more accurately than the visually inaccessible margin (subgingival). Based on these and other findings,18,72-76 subgingival margins should be avoided except for the following specific situations: (1) esthetic demands, (2) caries removal, (3) subgingival tooth fracture, (4) to cover existing subgingival restorations, (5) to gain needed crown length, and (6) to provide a more favorable crown contour (that is, furcation involvement).

PONTIC DESIGN The design of pontics for fixed partial dentures has been clouded by empirical judgment. The so-called ‘‘sanitary pontic’’ is not new to dentistry.5,77,78 The ‘‘bullet-shaped’’ pontic has been advocated by some authors5,78,79 as a desirable design to reduce food accumulation. Nearly all authors agree that the ‘‘ridge-lap’’ pontic is undesirable from the point of view of tissue health (Fig. 11). 112

Fig. 15. A, The embrasure space between two adjacent pontics can be closed to gain strength and reduce plaque accumulation. B, Closing the embrasure between two adjacent pontics does not affect esthetics. Note that the embrasures are kept open next to the abutment teeth to facilitate access for oral hygiene.

Numerous investigators7,51,80,81 have reported that inflammation of the edentulous mucosa adjacent to pontics is probably a response to plaque accumulation VOLUME 93 NUMBER 2

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Fig. 16. A, Modification (m) of tooth preparation to allow for placement of attachment system within the normal contour of the tooth. B, Castings with precision attachments for patient in Fig. 15, a. Note the open embrasures, high contacts, flatnot-fat contours, and the intracoronal attachments are within the confines of the normal crown contour.

Fig. 17. The coping approach to reconstruction can be designed to facilitate the access for oral hygiene guidelines. A, Copings in place. B, Suprastructure cemented onto copings. Note the open embrasures, flat buccolingual contours, and fluted molar furcations.

on the surface of the pontics. Many authors5,78,82-88 feel that glazed porcelain is the material of choice for contact against the edentulous ridge. Other investigators7,81,87-89 have shown that there is no clinical or histologic difference in the response of the mucosa to pontics properly constructed of cast gold, acrylic resin, or glazed or unglazed porcelain. Stein’s81 classic article on pontic design was largely responsible for a change in philosophy from a ‘‘sanitary’’ or ‘‘bullet-shaped’’ design to what is now commonly called a ‘‘modified ridge-lap’’ design. The modified ridge-lap design in the posterior region (Fig. 12) and the ridge-lap facing design in the anterior region (Fig. 13) offer minimal tissue contact, acceptable cosmetic value, proper cheek support, and accessibility for adequate oral hygiene.14,18,44,81 It has now been established that the design of the pontic may be the most important factor in preventing inflammatory reactions,81,89 not the material used in the pontic.

In addition to properly designing the undersurface of pontics, it is imperative to open embrasure spaces adjacent to abutments to allow room for interproximal tissue and access for oral hygiene (Figs. 12 and 13, part B).15,18,61,78,90,91 The occlusal surface should not be narrowed arbitrarily18 since this may create a food impaction and/or plaque retention situation similar to that of mal posed teeth (Fig. 14).5,81 The embrasure space between two adjacent pontics usually is closed to provide added strength, reduce food and plaque retention, and facilitate oral hygiene procedures under pontic areas (Fig. 15).92 Basic guidelines for the access-for-oral-hygiene theory of crown contour, margin placement, and pontic design can be applied to nearly all fixed restorative procedures. These guidelines apply to full porcelain coverage restorations (Figs. 12, B, 14, and 15, B), precision attachments (Fig. 16), and coping reconstructions (Fig. 17). Occasionally tooth preparations must be modified to allow for the added bulk needed for

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attachments, occlusal porcelain, and copings (Fig. 16, A). If proper tooth reduction is achieved, physiologic crown contours can be developed easily, regardless of the prosthesis being used.

SUMMARY Crown contours which promote favorable tissue response follow these guidelines: (1) buccal and lingual contours are flat; (2) embrasure spaces should be open; (3) contacts should be high (incisal one third) and buccal to the central fossa (except between first and second molars); and (4) furcations should be ‘‘fluted’’ or ‘‘barreled out.’’ Margins should be supragingival where possible. The pontic design of choice is the modified ridge lap for posterior spaces and the ridge-lap facing for anterior spaces. REFERENCES 1. Wheeler RC. Some fundamentals in tooth form. Dent Cosmos 1928;70: 889. 2. Wheeler RC. Restoration of gingival or cervical margins in full crowns. Dent Cosmos 1931;73:238. 3. Wheeler RC. Dental anatomy, physiology and occlusion. eds 1-4. Philadelphia: Saunders; 1940, 1950, 1958, 1965. 4. Kraus B, Jordan R, Abrams L. Dental anatomy and occlusion. Baltimore: Williams & Wilkins; 1967. 5. Glickman I. Clinical periodontology. eds 1-4. Philadelphia: W. B. Saunders; 1953, 1958, 1964, 1966. 6. Goldman H, Cohen DW. Periodontal therapy. eds 1-4. St. Louis: Mosby; 1956, 1960, 1964, 1968. 7. Henry P, Johnston J, Mitchell D. Tissue changes beneath fixed partial dentures. J Prosthet Dent 1966;16:937. 8. Wheeler RC. Complete crown form and the periodontium. J Prosthet Dent 1961;11:722. 9. Wheeler RC. Dental anatomy, physiology and occlusion. 4th ed. Philadelphia: Saunders; 1965. p. 112. 10. Vogan WI. The effect of bucco-lingual crown contours on gingival health, a reappraisal. J Prev Dent 1976;3:30. 11. Loe H, Theilade E, Jensen S. Experimental gingivitis in man. J Periodontol 1965;36:177. 12. Schwartz R, Massler M, LeBeau L. Gingival reactions to different types of tooth accumulated materials. J Periodontol 1971;42:144. 13. Socransky S. Relationship of bacteria to the etiology of periodontal disease. J Dent Res 1970;49:203. 14. Eissmann H, Radke R, Noble W. Physiologic design criteria for fixed dental restorations. Dent Clin North Am 1971;15:543. 15. Morris M. Artificial crown contours and gingival health. J Prosthet Dent 1962;12:1146. 16. Morris M. The position of the margin of the gingiva. Oral Surg 1958;11: 969. 17. Yuodelis R, Weaver J, Sapkos S. Facial and lingual contours of artificial complete crown restorations and their effect on the periodontium. J Prosthet Dent 1973;29:61. 18. Schluger S, Yuodelis RA, Page RC. Periodontal disease. Philadelphia: Lea & Febiger; 1977. p. 586-617. 19. Koivumaa K, Wennstrom A. A histologic investigation of the changes in gingival margins adjacent to gold crowns. Odontol Tidsskr 1960;68:373. 20. Perel M. Axial crown contours. J Prosthet Dent 1971;25:642. 21. Arnim S. The use of disclosing agents for measuring tooth cleanliness. J Periodontol 1963;34:227. 22. Lindhe J, Wicen P. The effects on the gingivae of chewing fibrous foods. J Periodont Res 1969;4:193. 23. Wade A. Effect on dental plaque of chewing apples. Dent Practice 1971; 21:194. 24. Wilcox C, Everett F. Friction of the teeth and the gingiva during mastication. J Am Dent Assoc 1963;66:513. 25. Herlands R, Lucca J, Morris M. Forms, contours, and extensions of full coverage in occlusal reconstruction. Dent Clin North Am 1962;6:147.

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26. Veldkamp D. The relationship between tooth form and gingival health. Dent Practice 1963;14:158. 27. Wagman S. Tissue management for full cast veneer crowns. J Prosthet Dent 1965;15:106. 28. Wagman S. The role of coronal contour in gingival health. J Prosthet Dent 1977;37:280. 29. Salkind A, Oshram H, Mandel I. Materia alba and dental plaque. J Periodontol 1974;45:489. 30. Keys P. Research in dental caries. J Am Dent Assoc 1968;76:1357. 31. Loe H, Von de Fehr F, Schiott C. Inhibition of experimental caries by plaque prevention, the effects of chlorhexidine mouthrinses. Scand J Dent Res 1967;80:1. 32. Von der Fehr F, Loe H, Theilade E. Experimental caries in man. Caries Res 1970;4:131. 33. Schluger S, Yuodelis RA, Page RC. Periodontal Disease. Philadelphia: Lea & Febiger; 1977. p. 81-7. 34. Sackett B, Gildenhuys R. The effect of axial crown over contour in adolescents. J Periodontol 1970;47:320. 35. Ramfjord S. Periodontal aspects of restorative dentistry. J Oral Rehabil 1974;1:107. 36. Burch J, Miller J. Evaluating crown contours of a wax pattern. J Prosthet Dent 1973;30:454. 37. Okeson J, Laswell H. Periodontal health through restorative contour. J Indiana Dent Assoc 1976;55:17. 38. Page RC, Schroeder HE. Pathogenesis of inflammatory periodontal disease. A summary of current work. Lab Invest 1976;33:235. 39. Barkley RF. Preventative philosophy of restorative dentistry. Dent Clin North Am 1971;15:569. 40. Pennel B, Keagle J. Predisposing factors in the etiology of chronic inflammatory periodontal disease. J Periodontol 1977;48:517. 41. Weinberg LA. Esthetics and the gingiva in full coverage. J Prosthet Dent 1960;10:737. 42. Beaudreau D. Tooth form and contour. J Am Soc Prev Dent 1973;3:36. 43. Beaudreau D. Procedures in general dentistry that affect the periodontium. In: Goldman H, Cohen DW, editors. Periodontal therapy. St. Louis: Mosby; 1968. p. 956-8. 44. Graver H. Restorative dentistry must be preventative dentistry. J Prev Dent 1976;3:17. 45. Hazen S, Osborne J. Relationship of operative dentistry to periodontal health. Dent Clin North Am 1967;11:245. 46. Linkow L. Contact areas in natural dentitions and fixed prosthodontics. J Prosthet Dent 1962;12:132. 47. Amsterdam N, Fox L. Provisional splinting—Principles and techniques. Dent Clin North Am 1959;3:73. 48. Townsend JD. A study of the relationship between artificial crown contour and dental plaque distribution, with and without oral hygiene. Thesis, University of Washington Library, 1973. 49. Gjermo P, Flotra L. The plaque removing effect of dental floss and toothpicks; a group comparison study. J Periodont Res 1969;4:170. 50. Schluger S, Yuodelis RA, Page RC. Periodontal Disease. Philadelphia: Lea & Febiger; 1977. p. 358-60. 51. Wise M, Dykema R. The plaque retaining capacity of four dental materials. J Prosthet Dent 1975;33:178. 52. Burch J. Periodontal considerations in operative dentistry. J Prosthet Dent 1975;34:156. 53. Burch J. Ten rules for developing crown contours in restorations. Dent Clin North Am 1971;15:611. 54. Black GV. Operative dentistry. Vol 1. 4th ed. Chicago: Medico-Dental; 1920. p. 208-19. 55. Stein R, Glickman I. Prosthetic considerations essential for gingival health. Dent Clin North Am 1960;4:177. 56. Tylman SD. The theory and practice of crown and fixed partial prosthodontics. 6th ed. St. Louis: Mosby; 1970. p. 94. 57. Marcum J. The effect of crown marginal depth upon gingival tissue. J Prosthet Dent 1967;17:479. 58. Preston JD. Rational approach to tooth preparation for ceramo-metal restorations. Dent Clin North Am 1977;21:683. 59. Silness J. Periodontal conditions in patients treated with dental bridges. Part III. The relationship between the location of the crown margin and the periodontal condition. J Periodont Res 1970;5:225. 60. Orban B. Biological considerations in restorative dentistry. J Am Dent Assoc 1941;28:1069. 61. Bass CC. A demonstrable line on extracted teeth indicating the location of the outer border of the epithelial attachment. J Dent Res 1946;25:401.

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62. Saglic R, Johansen J, Tollefsen T. Plaque-free zones on human teeth in periodontitis. J Clin Periodontol 1975;2:190. 63. Karlsen K. Gingival reactions to dental restorations. Acta Odontol Scand 1970;28:895. 64. Newcomb G. The relationship between the location of subgingival crown margins and inflammation. J Periodontol 1974;45:151. 65. Ricter W, Hirashi J. Relation of crown margin placement to gingival inflammation. J Prosthet Dent 1973;30:156. 66. Silness J. Periodontal conditions in patients treated with dental bridges. Part II. The influence of full and partial crowns on plaque accumulation, development of gingivitis and pocket formation. J Periodont Res 1970;5: 219. 67. Waerhaug J. Justification for splinting in periodontal therapy. J Prosthet Dent 1969;22:201. 68. Waerhaug J, Zander H. Reaction of gingival tissues to self-curing acrylic restorations. J Am Dent Assoc 1957;54:760. 69. Charbeneau G, Cartwright C, et al. Principles and Practices of Operative Dentistry. Philadelphia: Lea & Febiger; 1975. p. 102-23. 70. Valderhaug J. Periodontal conditions in patients five years following insertion of fixed partial dentures. J Oral Rehabil 1976;3:237. 71. Christensen G. Marginal fit of gold inlay castings. J Prosthet Dent 1966; 16:297. 72. Fox EC. Interdependence of operative treatment and periodontal treatment. Dent Health 1965;4:41. 73. Fuder EJ, Jameson HC. Depth of the gingival sulcus surrounding young permanent teeth. J Periodontol 1963;34:457. 74. Gordon I. The danger zone, use and abuses of full coverage. Alpha Omegan 1962;55:126. 75. Larato D. The effect of crown margin extension in gingival inflammation. J South Calif Dent Assoc 1969;37:476. 76. Mormann W, Regolati B, Renggli H. Gingival reaction to well-fitted subgingival proximal gold inlays. J Clin Periodontol 1974;1:120. 77. Tinker ET. Sanitary dummies. Dent Rev 1918;32:401. 78. Tylman SD. Theory and practice of crown and bridge prosthodontics. 5th ed. St. Louis: Mosby; 1965. p. 822-65.

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79. Smith DE. The pontic in fixed bridgework. Pacific Dent Gazette 1928;36: 741. 80. Clayton J, Green E. Roughness of pontic materials and dental plaque. J Prosthet Dent 1970;23:407. 81. Stein RS. Pontic–residual ridge relationship: A research report. J Prosthet Dent 1966;16:251. 82. Cavazos E. Tissue response to fixed partial denture pontics. J Prosthet Dent 1968;20:143. 83. Cooley RC. Porcelain pontics. J Am Dent Assoc 1938;25:1954. 84. Klaffenbach AO. Bridge pontics with porcelain tips or saddles. Dent Digest 1932;38:238. 85. Kroop M. Kroop pontic, new type of porcelain pontic. Dent Outlook 1939;26:14. 86. Pearson HH. Porcelain pontics. Dent Cosmos 1927;69:210. 87. Podshadley A. Gingival response to pontics. J Prosthet Dent 1968;19:51. 88. Podshadley A, Harrison T. Rat connective tissue response to pontic material. J Prosthet Dent 1966;16:110. 89. Jones R. Pontic design in fixed prosthodontics. In: Goldman H, Cohen DW, editors. Current therapy in dentistry, vol 4. St. Louis: Mosby; 1970. p. 259-69. 90. Johnston J, Phillips R, Dykema R. Pontic form. In: Modern practice in crown and bridge prosthodontics. 2nd ed. Philadelphia: Saunders; 1965. p. 278-99. 91. Ross I. Problems connected with combined periodontal therapy and fixed restorative care. Dent Clin North Am 1972;16:47. 92. Behrend DA. The mandibular fixed partial denture. J Prosthet Dent 1977; 37:622.

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