Maintaining and enhancing prosthodontics Jonathan
L. Ferencz,
gingival
architecture
in fixed
D.D.S.*
New York University, College of Dentistry, New York, N.Y. The long-term success of fixed prosthodontic restorations is greatly dependent upon the health and stability of the surrounding periodontal structures. This article deals with the interrelationship between tixed prosthodontic procedures and the stability and health of the periodontium. The commonly encountered problem of alterations in gingival architecture is examined in relation to tooth preparation as well as soft tissue preparation. In addition, the ability of the provisional restoration to guide soft tissue form is discussed as well as the role of the final restoration in providing long-term tissue maintenance. Key factors such as margin placement, tissue damage during tooth preparation, the role of the provisional restoration, tissue injury during impression procedures, crown contour, pontic design, and embrasure design are covered in detail. (J PROSTHET DENT1991;65:650-7.)
T
he successof fixed prosthodontic restorations is largely dependent upon the long-term health and stability of the surrounding periodontal structures. There is a tendency in fixed prosthodontics, however, to emphasize technical proceduresupon which the quality of most restorations is based.It is alsowell establishedthat the single most important criterion on which the successof fixed prosthodontic procedures can be measuredis the establishment and maintenance of periodontal health.l No single restoration in dentistry is more dependent upon nor influencesmore the health of periodontal structures than the full coveragerestoration. This article examines those factors that contribute to periodontic-prosthodontic success,survey the literature, and attempt to relate this information to problems in clinical practice. It has been well documented that the health of the periodontal tissuesmust be achievedprior to initiation of restorative procedures.2l3Gingival tissues should exhibit knife-edge margins with firm papillae, sulcular depths within the range of 1 to 3 mm, and adequate bands of attached tissue before one commencesfixed prosthodontic procedures. Tooth preparations begun before gingival health is achieved can result in severeuntoward responses, most notably extreme gingival recession.In addition, an adequate zone of keratinized tissue is essentialto act as a barrier to the potential insults of restorative techniques.
suggestedthat full crown margins be located as close as possibleto the gingival attachment to minimize the possibility of gingival trauma.4 However, the most literature on this subject advocates the use of supragingival margin placement whenever possible. Waerhaug5 stated that “There is no doubt that subgingivalrestorations are among the major etiologic factors in periodontitis.“5 He felt that inflammation of the gingiva around subgingival restorations may be due to inflammation causedby the nature of the materials located in the gingival sulcus, overhanging margins,rough surfaces,retained plaque or a combination of these factors. These ideaswere confirmed by Marcum,6 who found that crownslocated at or even with the gingival crest caused the least inflammatory responses.In an extensive study by Larato,‘l in which he observed 546 crownsin 266patients, 21% of the crownswith marginsat or above the gingival crest showedgingival inflammation, compared with 63% of the crowns with subgingival margins. Silness8found that teeth with full crownsshowedgreater amounts of soft deposits, more severe gingivitis, and increased pocket depth when compared with teeth with partial crowns. Karlseng studied dogs and monkeys and concluded that gingival inflammation was present in almost all subgingival margin placementa and that these conditions wererelated to margin fit more than to any other
MARGIN
factor. A similar study by Newcomb1o concluded that the further into the sulcus the margin was placed, the more likely would be the occurrence of gingival inflammation.
Margins
PLACEMENT of full crowns may be located above, at, or be-
low the crest of gingival margins. At one time it was
Presented at the Academy of Denture Presthetics meeting, Corpus Christi, Tex. *Clinical Professor, Department of Prosthodontics end Occlusion.
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The least amount of inflammation was observed when margins were placed at the gingival crest or just into the gingival crevice. Silnessli examined 351fixed partial dentures and found that subgingival restorations resulted in lessfavorable periodontal reactions than supragingival or crestal margins. Margins located close to the epithelial attachment produced more harm than margins further away. He listed re-
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Fig. 1. Fig. 2. Fig. 3. Fig. 4. gingival
RESTORATIONS
Preexisting crown on left incisor with gingival recession. Tooth reprepared for new metal ceramic crown. New metal ceramic crown in place on left incisor. Periodontal probe in place to measure sulcular depth prior to placement of subbevel.
storative procedures, restorative materials, surface roughness, splinting of adjacent teeth, and pontics in fixed partial dentures as possible factors. A study by Richter and Ueno12 examined the relationship between the location of crown margins and gingival inflammation on 12 molars with one half of the preparation supragingival and the other half subgingival. No difference was found in the health of the gingiva using Liie’s gingival index to judge gingival tissue reaction. They reported no change in sulcular depth, gingival contour, or plaque accumulation. They concluded that the fit and finish of full crown restorations may be more important to gingival health than the location of the finish line. Even though the results of these studies are not entirely consistent with each other, one can safely conclude that (1) subgingival crown margins generally result in a less favorable periodontal condition than margins at the gingival crest or above and (2) subgingival margins placed near the bottom of the sulcus are potentially more damaging than margins placed closer to the crest. The etiology of this inflammatory process may be related to the injurious nature
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of the subgingival operative procedures, restorative materials themselves, marginal gaps, and roughness of the luting agent. Several mitigating factors necessitate the placement of margins within the gingival sulcus. These include esthetics, preexisting restorations, retention requirements, root caries, severe cervical defects, and root sensitivity. Although esthetics is cited frequently as the most important reason for subgingival margin placement, studies by Crispin and Watsonr3-15 have shown that esthetics may not be as overwhelming a factor for the patient as it is for the dentist. Their studies indicate that routine subgingival margin placement may be unnecessary, since a significant percentage of patients do not show anterior and posterior gingival margins even with an exaggerated smile and, given an understandable explanation of the periodontal benefits, the patient will accept supragingival crown margins. Teeth requiring full coverage restorations often have preexisting restorations that extend into sulcular spaces, ranging from small cervical restorations to preexisting complete crowns. It is frequently necessary to extend crown
651
FERENCZ
Fig. 5. Gingival recession on right lateral incisor caused by preparation procedures and overcontouring. Fig. 6. Replacement metal ceramic crown for left lateral incisor. Fig. 7. Preexisting provisional restorations on incisors and canine teeth. Fig. 8. Gingival response after 1 week with new provisional restorations for canines and incisors.
margins below these defects to ensure an adequate marginal seal. The same thing is true for teeth with cervical abrasions where subgingival margin placement tends to protect these teeth from further abrasion and may help protect them from fracture. However, the literature, does not lend much credence to the concept that subgingival margin placement eliminates root caries. Valderhaug and Birkeland16 found that the subgingival placement of crown , margins gave no reliable protection against new caries. Retention is an important factor in the long-term success of fixed restorations. Many restorations fail because tooth preparations lack suflicient retention to withstand the forces to which they are subjected. Extension into the gingival sulcus is not the only way to deal with questionable retention. Decreasing the convergence angle of the preparation or adding retentive features such as pins or grooves will often be sufficient. In many instances, however, crown margins should be placed in the gingival sulcus. These restorations, which might be better termed “intracrevicu1ar,“17 since they are
652
placed in the space bounded by the tooth and the sulcular epithelium, have great potential for injury to the periodontium. They also offer some of dentistry’s greatest potential for the esthetic and functional recreation of missing tooth structure. The success of these restorations is measured by the long-term maintenance of gingival architecture and is dependent upon nontraumatic techniques for fabrication, accurate marginal adaptation, biologic contours, and scrupulous postinsertion maintenance (Figs. 1 through 3).
TISSUE RESPONSE PREPARATION
TO TOOTH
Preparation of teeth below the gingiva at speeds of 260,oOOrpm with rapid cutting instruments causes trauma of varying severity to the sulcular epithelium and frequently to the subepithelial connective tissue. When bleeding O&XUS during tooth preparation, it implies abrasion to the epithelial lining of the sulcus and exposure to the underlying connective tissue. Most authorities agree that
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Fig. Fig. Fig. Fig.
RESTORATIONS
9. Gingival retraction cord placed in sulcus prior to impression making. 10. Appearance of gingival sulcus immediately following removal of cord. 11. Anterior teeth prepared with intracrevicular bevel. 12. Reversible hydrocolloid impression.
these lesions are reversible and will heal if left undisturbed and conditions are favorable.‘* A new epithelium will proliferate to cover the exposed connective tissue wound and complete healing will normally take place within 8 to 14 days. However, if the connective tissue fibers that anchor to cementum are damaged, chances are that during the healing process there will be an epithelial downgrowth establishing the bottom of the sulcus at a more apical level. It is obvious that the subgingival preparation should extend as little as possible into the gingival sulcus. Those preparations placed excessively deep within the sulcus to enhance esthetics result in more recession and often a less esthetic result than those that slightly enter the sulcus. There can be no doubt that an understanding of the periodontal mechanism of wound healing dictates that subgingival margins should enter the sulcus to a minimal extent. Furthermore, all attempts should be made to minimize bleeding during tooth preparation, since it is quite possible that there may have been an irreversible injury to the underlying connective tissue. When the tissue is healthy prior to tooth preparation, slight bleeding, which implies abrasion of the sulcular epithelium, is usually insignificant.
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However, when there is considerable bleeding, postponing the impression until the sulcular wound has healed completely will minimize the chance of gingival recession around the final restoration. Once the sulcular wound has healed, the marginal surface may have to be reprepared to reestablish the subgingival margin with respect to the new tissue level. When preparing the tooth within the gingival sulcus, knowledge of the sulcular depth is imperative. Only by knowing the parameters of this space can one accurately judge the depth of penetration (Fig. 4). Typical extension into the gingival sulcus should not exceed 0.5 to 1 mm, depending upon the depth of the sulcus. In locations of critical esthetic requirements, the shoulder or chamfer should be placed slightly beneath the crestal tissue and a rather short bevel used. Long bevels in this region may result in unsightly esthetics. Underreduction in thii part of the preparation must be avoided to enaure that the final restoration is not overcontoured in the critical cervical region. Attempts to compensate for an inadequate preparation by covering the metal collar with porcelain for a metal ceramic crown or overcontouring the cervical surface of the resto-
Fig. Fig. Fig. Fig.
13. 14. 16. 16.
Stone cast showing widened gingival sulcus. Ovate pontic form for teeth. Embrasure is tested with interproximal brush. Tufted dental floss used to clean embrasure.
ration usually result in recession of the gingival tissues in a short period of time. In some instances, placement of a longer bevel, either to increase the retention of the casting or to attempt to augment the strength of an endodontically treated tooth may be indicated. In these situations the shoulder or chamfer with a long bevel should be placed at the height of the gingival tissue, or even supragingivally, to preclude the possibility of tissue destruction within the sulcus. Excessively deep penetration into the gingival sulcus is one of the most serious errors in tooth preparation, with the obvious risk of injury to the epithelial attachment long with other problems that are created if the margin is more than 1 mm below the gingival crest. It is nearly impossible to capture the margins of such deep preparations while making provisional restorations and extremely difficult to thoroughly remove all remnants of temporary cement. Impression making becomes extraordinarily di6icult and increasingly traumatic when the placement of margins is excessively deep within the sulcus. In addition, it is difficult
654
to validate marginal accuracy when working far beneath the tissue and it is likely that traces of the cement after insertion, may remain in the s&us. Often a preparation extends minimally into the sulcus on the facial surface but the dentist inadventently keeps the preparation at the same level on the interproximal surfaces as well. This procedure often disregards the parabolic architecture of the peridontal housing supporting the tooth and does considerable damage to the interproximal soft tissues. This damage is more often seen in the anterior region where the alveolus is narrow rather than in the posterior region where the alveolar process must be wide to accommodate the larger root surface (Figs. 5 and 6). During tooth preparation, regardless of the preparation design, it is critical that the dentist not injure the junctional epithelium or the connective tissue fiber apparatus, otherwise the gingival margin as well as the alveolar crest is likely to recede. If gingival recession can be avoided during the restorative phase, a major cosmetic problem may be avoided.
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The provisional restoration is often neglected in fixed prosthodontics.i9 Its role with respect to periodontal health during fixed procedures is critically important. The provisional restoration often plays an important part in improving periodontal health prior to final preparation and in making the impression. Complex fixed restorations are often needed to replace old, worn, or inadequate restorations. The tissue changes that are seen around these defective restorations can frequently be reversed with well-fitting, properly contoured acrylic resin provisional restorations. If the damage to the periodontium is limited to the soft tissues, the effects usually are reversible once the provisional restorations are in place for a few weeks. The provisional restoration provides a matrix against which the tissue heals, guiding the generation of correct soft tissue architecture (Figs. 7 and 8). Even in patients with more severe periodontal disease, a well constructed provisional restoration can greatly improve soft tissue tone, thereby simplifying the ensuing periodontal procedures. Even though the patient with advanced periodontal disease usually requires osseous surgery to correct aberrant hard tissue architecture, a wellformed provisional restoration has the potential to greatly reduce inflammation, thereby simplifying the surgical procedures and speeding healing. During inital tooth preparation, it is important not to prepare the tooth to its full depth within the sulcus. Margins that are less invasive within the sulcus can be captured accurately when fabricating provisional restorations. This is essential to improve the soft tissue status at this time. An important requirement of the provisional restoration is that it have an accurate marginal seal. Without marginal seal, tissue health does not improve drastically. Proper form in the cervical portion of the provisional restoration is also needed for gingival health. The contour as it emerges from the sulcus is most often flat with no obvious bulge or height of contour. The form of the interproximal embrasure also greatly influences the ability of the soft tissue to resume its normal architecture. Embrasure spaces of the provisional restoration must be opened sufficiently to allow for interproximal cleansing with cleaning aids such as interproximal brushes or tufted dental floss. At this time, patients should be instructed in plaque removal around the provisional restorations. Provisional restorations are cemented with temporary cements that need to be sufficiently retentive to allow for normal function by the patient, while at the same time permitting removal by the dentist, if necessary. Failure to remove all traces of temporary cement from the sulcus or interproximal space negates much of the therapeutic potential of the provisional restoration. These irritants can result in inflammation of the marginal gingiva or interproximal papillae that will also se-
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verely compromise management.
IMPRESSION
efforts to maintain ideal soft tissue
PROCEDURES
Impression making of tooth preparations that extend subgingivally with an elastic material also has the potential for soft tissue abuse. Adequate gingival retraction is essential for predictable impression making. Although techniques for retraction have often been debated, the use of retraction cord has proved to be an effective method of soft tissue management during the impression phase. The placement of retraction cord and cotton strings into the gingival sulcus may cause injury to the sulcular epithelium.20 The damage inflicted to the soft tissue depends upon the chemical agent with which the cord has been impregnated, the force used in packing the cord, and the length of time the cord is left in place within the sulcus. The force used to place the cords should be minimal to avoid forcing the cord into the subepithelial connective tissue, Most importantly, prior to its removal, the cord should be moistened to avoid stripping the sulcular epithelium (Figs. 9 and 10). The placement of an intracrevicular bevel can be most helpful as a first step in gingival retraction. A bevel made with a fluted finishing bur or with a fine diamond creates a space, at the expense of the tooth surface not the inner tissue wall, which is adequate to accommodate retraction cord. Although the inner lining of the sulcular epithelium is usually abraded during the placement of the bevel, if no damage is inflicted to the underlying connective tissue healing takes place uneventfully, without recession. The removal of tooth structure in the placement of the intracrevicular bevel can be accomplished without premanent injury to the soft tissue. A widened sulcus can thus be obtained that is wide enough to accept retraction cord. In this manner the cord is placed rather than packed into the sulcus and gingival retraction procedures can be performed without causing permanent damage to the soft tissue (Figs. 11 through 13).
CROWN
CONTOUR
It is generally accepted that the “protective bulge” theory of human tooth contours is not compatible with current concepts of dental anatomy and periodontics.21 The belief that the purpose of facial and lingual enamel bulges of human teeth is to protect the marginal gingiva from the traumatic effects of mastication is no longer widely held. Now, it is universally accepted that the principal etiologic factor in both caries and periodontal disease is bacterial plaque. Therefore any tooth contour that promotes the retention of microbial plaque must be avoided. Overcontouring tends to encourage the retention of plaque and the ensuing development of inflammation. Conversely, the undercontoured tooth (enamel hyperplasia, cervical erosion, peg-shaped
655
lateral incisor) rarely shows signs of gingival inflammation. Pere122 studied the relationship between axial tooth contours and the surrounding marginal gingiva in six dogs. He found that undercontouring did not produce any significant changes in gingival health, while overcontouring produced inflammatory and hyperplastic changes in the marginal tissues. For these reasons, the final restoration should follow the contour established by the root anatomy. The cervical third of the restoration should emerge from the gingival sulcus as flat as possible, especially in regions where it is difficult to maintain effective oral hygiene, such as fluted areas and furcated molars. An attempt should be made to flatten the facial and lingual contours of restorations to enable the most effective removal of plaque.
PONTIC
DESIGN
Stein23 has described the ideal pontic design as a “modified ridge lap” in the posterior region and a “lap facing” in the anterior region. He stated that the ideal tissue-contacting surface should be smooth and finely finished to offer a maximum level of cleansibility. No advantage seems to be served by using porcelain, acrylic resin, or gold as the tissue-contacting surface. What seems to be more important is the degree to which the tissue surface is polished. From a periodontal point of view, pontics represent oral hygiene problems for patients and therefore should be constructed to facilitate plaque removal. Ideally, there should be no contact or very slight contact between the tissue-contacting surface and the ridge mucosa, since histologic changes in the ridge tissues seem to be related to the amount of tissue covered by the pontic.24 As much as the shape of the residual ridge will allow, the tissue-contacting surface should be flat or convex, allowing for plaque removal by the passing of dental floss. Also, pontics should be the same length as the adjacent teeth. This can be achieved by shortening the gingival portion until the correct length is achieved. From a practical standpoint, pontic design must often be modified in favor of esthetics, either by covering more of the ridge surface or by creating an “ovate pontic design.“25 The pontic form that is chosen for a given situation should balance the factors of cleansibility and esthetics. In any case, the ridge tissue should be well keratinized, free of irregularities that would not permit adequate oral hygiene, and be in minimal contact with a highly polished surface (Fig. 14).
EMBRASURE
DESIGN
Embrasure contours might be more important than facial or lingual crown contours.26 The interproximal papilla responds rapidly to overcontouring of the embrasure region. It becomes inflamed and hypertrophied as a result of poor oral hygiene when the interproximal embrasure is impinged upon by overcontoured adjacent crown surfaces.
656
Other factors may contribute to the papillary inflammatory often seen between splinted restorations. The papilla is likely to be inflamed because of the presence of subgingival margins on either side and is often constricted in an occlusal-gingival direction by the interproximal soldered connection. A study to determine whether there were embrasure dimensions that were more favorable to the health of the gingiva and underlying mucosa concluded that oral hygiene exerted a more important influence than the height of the embrasure.27 The ideal size of the interproximal embrasure is one that permits the introduction of cleaning aids for the removal of plaque in this most vital area (Fig. 15). Embrasures that are excessively opened impact negatively upon esthetics, impair phonetics, and allow excessive lateral food impaction. The patient with normal clinical crown length often presents a dilemma when one is designing an ideal embrasure form. Interproximal height is often not sufficient to allow space for an interproximal brush without weakening the interproximal connector. Tufted dental floss can be used in these situations, especially for anterior teeth (Fig. 16). The patient with advanced periodontal disease usually presents much more interproximal height, and in some instances, has so much apical migration of the attachment apparatus that the embrasure space is excessively wide, which leads to esthetic, phonetic, and food impaction problems. This predicament can be further complicated by root proximity problems, cervical concavities, and root anatomy irregularities. Correct embrasure form often requires a balancing of all the factors mentioned.
LONG-TERM
MAINTENANCE
The trauma to the periodontal apparatus caused by tooth preparation, provisional restorations, gingival retraction, and impression procedures is often reversible. In addition to the design of the restoration, the marginal adaptation is likely to affect the peridontal structures on a permanent basis. The subgingival area (the crown margin, the luting agent, and the prepared tooth) often accounts for the destructive effects on the soft tissue frequently seen adjacent to subgingival restorations. This area tends to be a refuge for bacteria and necrotic tissue. Several sources of surface roughness can exist in this subgingival area. From a periodontal point of view, all restorative margins are ill-fitting and rough. Even carefully polished surfaces and exact margins are irregular when examined microscopically. In addition, the luting agents used for cementation tend to be porous and leave a very rough surface to which microbial products may adhere. These rough surfaces are like calculus in that they are continuously coated with bacterial plaque and are responsible for an ever-deepening sulcus. Unlike calculus, however, ill-fitting margins cannot be easily removed and they represent a much greater problem for the periodontist.
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After cementation, all remnants of excess cement must be removed. In addition, the junction of the crown margin and the tooth finishing line, an area filled with cement, should be smoothed as much as possible with curettes to reduce the roughness of the luting agent. Roughness at the interface of tooth and restoration cannot be totally eliminated, but if the restoration is properly fabricated and finished, the slight remaining roughness can be well tolerated by the soft tissues. Long-term stability of the intricate relationship between the restoration and the periodontal structures requires the active involvement of the patient and the dentist. Once the restoration has been constructed with adherence to all the factors governing the achievement of optimal soft tissue health and is placed into this healthy environment, a strict maintenance regimen can ensure its survival. Adequate plaque removal by a well motivated patient, as well as careful maintenance visits, are essential for the preservation of this delicate state of coexistence between the soft tissue and the restoration. With effective plaque control, routine scaling, follow-up radiographs, and a careful evaluation of sulcular health at regular intervals, it is realistic to expect the soft tissue architecture to remain quite stable for a long period of time.
REFERENCES
7. Larato DC. The effect of crown margin extension to gingival inflammation. J South Calif Dent Assoc 196%37:476-l+. 8. Silness J. Periodontal conditions in patients treated with dental bridges. J Periodont Res 1970;5:219-24. Acta Odontol 9. Karlsen K. Gingival reactions to dental restorations. Stand 1970;28:895-904. 10. Newcomb GM. The relationship between the location of subgingival crown margins and gingival inflammation. J Periodontol1974;45:151-4. 11. Silness J. Fixed prosthodontics and periodontal health. Dent Clin North Am 1980;24:317-29. 12. Richter WA, Ueno H. Relationship of crown margin placement to gingival inflammation. J PROSTHET DENT 1973;30:156-61. 13. Crispin BJ, Watson JF. Margin placement of esthetic veneer crowns. Part 1. Anterior tooth visibility. J PROSTHET DENT 1981;45:278-82. 14. Crispin BJ, Watson JF. Margin placement of esthetic veneer crowns. Part II. Posterior tooth visibility. J PROSTHET DENT 1981;45:389-91. 15. Watson JR, Crispin BJ. Margin placement of esthetic veneer crowns. Part III. Attitudes of patients and dentists. J PROSTHET DENT 1981; 45:499-501.
16. Valderhaug J, Birkeland JM. Periodontal conditions in patients 5 years following insertion of fixed prostheses. J Oral Rehabil 1976;3:237-43. 17. Nevins M, Skurow HN. The intracervicular restorative margin, the biologic width, and the maintenance of the gingival margin. Int J Peridontol Restor Dent 1984;3:31-49. 18. Liie H. Reactions of marginal tissues to restorative procedures. Int Dent J 196818759-78. 19. Shave11 HM. Mastering the art of tissue management during provisionalization and biologic final impressions. Int J Periodonto Restor Dent 1988325-43. 20. Liie H. Silness J. Tissue reactions to string packs used in fixed restorations. J PROSTHET DENT 1963;13:318-23. 21. Yuodelis RA, Weaver JD, Sapkos S. Facial and lingual contours of artificial complete crown restorations and their effects on the periodontium. J PROSTHET DENT 1973;29:61-6. 22. Perel ML. Axial crown contours. J PROSTHET DENT 1971;25:642-9. 23. Stein RS. Pontic-residual ridge relationship: a research report. J PROSTHET DENT
1. Stein RS. Glickman I. Periodontal considerations essential for gingival health. Dent Clin North Am 1960;4:177-88. 2. Shave11 HM. Mastering the art of tissue management and biologic final impressions. Int J Periodontal Res Dent 1988;3:25-43. 3. Nemetz H. Tissue management in fixed prosthodontics. J PROSTHET DENT
1974;31:628-36.
4. Wagman
SS. Tissue management
THET DENT
DENT
for full cast veneer crowns. J PROS-
1965;15:106-17.
5. Waerhaug J. Histologic considerations which govern where the margins of restorations should be located in relation to the gingiva. Dent Clin North Am 1960;4:161-76. 6. Marcum JS. The effect of crown margin depth upon gingival tissue. J PROSTHET DENT 1967;17:479-87.
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1966;16:251-85.
24. Henry PJ, Johnston JF, Mitchell DF. Tissue changes beneath fixed partial dentures. J PROSTHET DENT 1966$6:937-47. 25. Garber DA. The edentulous ridge in fixed prosthodontics. Compend Contin Ed 1981;II:212-24. 26. Morris ML. Artificial crown contours and gingival health. J PROSTHET 1962;12:1146-56.
27. Hirshberg SM. The relationship of oral hygiene to embrasure and pontic design-a preliminary study. J PROSTHET DENT 1972;27:26-38. Reprint
requests to:
DR. JONATHAN L. FERENCZ 37 PARK AVE. NEW YORK, NY 10016
657
L. Ferencz,
gingival
architecture
in fixed
D.D.S.*
New York University, College of Dentistry, New York, N.Y. The long-term success of fixed prosthodontic restorations is greatly dependent upon the health and stability of the surrounding periodontal structures. This article deals with the interrelationship between tixed prosthodontic procedures and the stability and health of the periodontium. The commonly encountered problem of alterations in gingival architecture is examined in relation to tooth preparation as well as soft tissue preparation. In addition, the ability of the provisional restoration to guide soft tissue form is discussed as well as the role of the final restoration in providing long-term tissue maintenance. Key factors such as margin placement, tissue damage during tooth preparation, the role of the provisional restoration, tissue injury during impression procedures, crown contour, pontic design, and embrasure design are covered in detail. (J PROSTHET DENT1991;65:650-7.)
T
he successof fixed prosthodontic restorations is largely dependent upon the long-term health and stability of the surrounding periodontal structures. There is a tendency in fixed prosthodontics, however, to emphasize technical proceduresupon which the quality of most restorations is based.It is alsowell establishedthat the single most important criterion on which the successof fixed prosthodontic procedures can be measuredis the establishment and maintenance of periodontal health.l No single restoration in dentistry is more dependent upon nor influencesmore the health of periodontal structures than the full coveragerestoration. This article examines those factors that contribute to periodontic-prosthodontic success,survey the literature, and attempt to relate this information to problems in clinical practice. It has been well documented that the health of the periodontal tissuesmust be achievedprior to initiation of restorative procedures.2l3Gingival tissues should exhibit knife-edge margins with firm papillae, sulcular depths within the range of 1 to 3 mm, and adequate bands of attached tissue before one commencesfixed prosthodontic procedures. Tooth preparations begun before gingival health is achieved can result in severeuntoward responses, most notably extreme gingival recession.In addition, an adequate zone of keratinized tissue is essentialto act as a barrier to the potential insults of restorative techniques.
suggestedthat full crown margins be located as close as possibleto the gingival attachment to minimize the possibility of gingival trauma.4 However, the most literature on this subject advocates the use of supragingival margin placement whenever possible. Waerhaug5 stated that “There is no doubt that subgingivalrestorations are among the major etiologic factors in periodontitis.“5 He felt that inflammation of the gingiva around subgingival restorations may be due to inflammation causedby the nature of the materials located in the gingival sulcus, overhanging margins,rough surfaces,retained plaque or a combination of these factors. These ideaswere confirmed by Marcum,6 who found that crownslocated at or even with the gingival crest caused the least inflammatory responses.In an extensive study by Larato,‘l in which he observed 546 crownsin 266patients, 21% of the crownswith marginsat or above the gingival crest showedgingival inflammation, compared with 63% of the crowns with subgingival margins. Silness8found that teeth with full crownsshowedgreater amounts of soft deposits, more severe gingivitis, and increased pocket depth when compared with teeth with partial crowns. Karlseng studied dogs and monkeys and concluded that gingival inflammation was present in almost all subgingival margin placementa and that these conditions wererelated to margin fit more than to any other
MARGIN
factor. A similar study by Newcomb1o concluded that the further into the sulcus the margin was placed, the more likely would be the occurrence of gingival inflammation.
Margins
PLACEMENT of full crowns may be located above, at, or be-
low the crest of gingival margins. At one time it was
Presented at the Academy of Denture Presthetics meeting, Corpus Christi, Tex. *Clinical Professor, Department of Prosthodontics end Occlusion.
10/l/23147
650
The least amount of inflammation was observed when margins were placed at the gingival crest or just into the gingival crevice. Silnessli examined 351fixed partial dentures and found that subgingival restorations resulted in lessfavorable periodontal reactions than supragingival or crestal margins. Margins located close to the epithelial attachment produced more harm than margins further away. He listed re-
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Fig. 1. Fig. 2. Fig. 3. Fig. 4. gingival
RESTORATIONS
Preexisting crown on left incisor with gingival recession. Tooth reprepared for new metal ceramic crown. New metal ceramic crown in place on left incisor. Periodontal probe in place to measure sulcular depth prior to placement of subbevel.
storative procedures, restorative materials, surface roughness, splinting of adjacent teeth, and pontics in fixed partial dentures as possible factors. A study by Richter and Ueno12 examined the relationship between the location of crown margins and gingival inflammation on 12 molars with one half of the preparation supragingival and the other half subgingival. No difference was found in the health of the gingiva using Liie’s gingival index to judge gingival tissue reaction. They reported no change in sulcular depth, gingival contour, or plaque accumulation. They concluded that the fit and finish of full crown restorations may be more important to gingival health than the location of the finish line. Even though the results of these studies are not entirely consistent with each other, one can safely conclude that (1) subgingival crown margins generally result in a less favorable periodontal condition than margins at the gingival crest or above and (2) subgingival margins placed near the bottom of the sulcus are potentially more damaging than margins placed closer to the crest. The etiology of this inflammatory process may be related to the injurious nature
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of the subgingival operative procedures, restorative materials themselves, marginal gaps, and roughness of the luting agent. Several mitigating factors necessitate the placement of margins within the gingival sulcus. These include esthetics, preexisting restorations, retention requirements, root caries, severe cervical defects, and root sensitivity. Although esthetics is cited frequently as the most important reason for subgingival margin placement, studies by Crispin and Watsonr3-15 have shown that esthetics may not be as overwhelming a factor for the patient as it is for the dentist. Their studies indicate that routine subgingival margin placement may be unnecessary, since a significant percentage of patients do not show anterior and posterior gingival margins even with an exaggerated smile and, given an understandable explanation of the periodontal benefits, the patient will accept supragingival crown margins. Teeth requiring full coverage restorations often have preexisting restorations that extend into sulcular spaces, ranging from small cervical restorations to preexisting complete crowns. It is frequently necessary to extend crown
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FERENCZ
Fig. 5. Gingival recession on right lateral incisor caused by preparation procedures and overcontouring. Fig. 6. Replacement metal ceramic crown for left lateral incisor. Fig. 7. Preexisting provisional restorations on incisors and canine teeth. Fig. 8. Gingival response after 1 week with new provisional restorations for canines and incisors.
margins below these defects to ensure an adequate marginal seal. The same thing is true for teeth with cervical abrasions where subgingival margin placement tends to protect these teeth from further abrasion and may help protect them from fracture. However, the literature, does not lend much credence to the concept that subgingival margin placement eliminates root caries. Valderhaug and Birkeland16 found that the subgingival placement of crown , margins gave no reliable protection against new caries. Retention is an important factor in the long-term success of fixed restorations. Many restorations fail because tooth preparations lack suflicient retention to withstand the forces to which they are subjected. Extension into the gingival sulcus is not the only way to deal with questionable retention. Decreasing the convergence angle of the preparation or adding retentive features such as pins or grooves will often be sufficient. In many instances, however, crown margins should be placed in the gingival sulcus. These restorations, which might be better termed “intracrevicu1ar,“17 since they are
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placed in the space bounded by the tooth and the sulcular epithelium, have great potential for injury to the periodontium. They also offer some of dentistry’s greatest potential for the esthetic and functional recreation of missing tooth structure. The success of these restorations is measured by the long-term maintenance of gingival architecture and is dependent upon nontraumatic techniques for fabrication, accurate marginal adaptation, biologic contours, and scrupulous postinsertion maintenance (Figs. 1 through 3).
TISSUE RESPONSE PREPARATION
TO TOOTH
Preparation of teeth below the gingiva at speeds of 260,oOOrpm with rapid cutting instruments causes trauma of varying severity to the sulcular epithelium and frequently to the subepithelial connective tissue. When bleeding O&XUS during tooth preparation, it implies abrasion to the epithelial lining of the sulcus and exposure to the underlying connective tissue. Most authorities agree that
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Fig. Fig. Fig. Fig.
RESTORATIONS
9. Gingival retraction cord placed in sulcus prior to impression making. 10. Appearance of gingival sulcus immediately following removal of cord. 11. Anterior teeth prepared with intracrevicular bevel. 12. Reversible hydrocolloid impression.
these lesions are reversible and will heal if left undisturbed and conditions are favorable.‘* A new epithelium will proliferate to cover the exposed connective tissue wound and complete healing will normally take place within 8 to 14 days. However, if the connective tissue fibers that anchor to cementum are damaged, chances are that during the healing process there will be an epithelial downgrowth establishing the bottom of the sulcus at a more apical level. It is obvious that the subgingival preparation should extend as little as possible into the gingival sulcus. Those preparations placed excessively deep within the sulcus to enhance esthetics result in more recession and often a less esthetic result than those that slightly enter the sulcus. There can be no doubt that an understanding of the periodontal mechanism of wound healing dictates that subgingival margins should enter the sulcus to a minimal extent. Furthermore, all attempts should be made to minimize bleeding during tooth preparation, since it is quite possible that there may have been an irreversible injury to the underlying connective tissue. When the tissue is healthy prior to tooth preparation, slight bleeding, which implies abrasion of the sulcular epithelium, is usually insignificant.
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However, when there is considerable bleeding, postponing the impression until the sulcular wound has healed completely will minimize the chance of gingival recession around the final restoration. Once the sulcular wound has healed, the marginal surface may have to be reprepared to reestablish the subgingival margin with respect to the new tissue level. When preparing the tooth within the gingival sulcus, knowledge of the sulcular depth is imperative. Only by knowing the parameters of this space can one accurately judge the depth of penetration (Fig. 4). Typical extension into the gingival sulcus should not exceed 0.5 to 1 mm, depending upon the depth of the sulcus. In locations of critical esthetic requirements, the shoulder or chamfer should be placed slightly beneath the crestal tissue and a rather short bevel used. Long bevels in this region may result in unsightly esthetics. Underreduction in thii part of the preparation must be avoided to enaure that the final restoration is not overcontoured in the critical cervical region. Attempts to compensate for an inadequate preparation by covering the metal collar with porcelain for a metal ceramic crown or overcontouring the cervical surface of the resto-
Fig. Fig. Fig. Fig.
13. 14. 16. 16.
Stone cast showing widened gingival sulcus. Ovate pontic form for teeth. Embrasure is tested with interproximal brush. Tufted dental floss used to clean embrasure.
ration usually result in recession of the gingival tissues in a short period of time. In some instances, placement of a longer bevel, either to increase the retention of the casting or to attempt to augment the strength of an endodontically treated tooth may be indicated. In these situations the shoulder or chamfer with a long bevel should be placed at the height of the gingival tissue, or even supragingivally, to preclude the possibility of tissue destruction within the sulcus. Excessively deep penetration into the gingival sulcus is one of the most serious errors in tooth preparation, with the obvious risk of injury to the epithelial attachment long with other problems that are created if the margin is more than 1 mm below the gingival crest. It is nearly impossible to capture the margins of such deep preparations while making provisional restorations and extremely difficult to thoroughly remove all remnants of temporary cement. Impression making becomes extraordinarily di6icult and increasingly traumatic when the placement of margins is excessively deep within the sulcus. In addition, it is difficult
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to validate marginal accuracy when working far beneath the tissue and it is likely that traces of the cement after insertion, may remain in the s&us. Often a preparation extends minimally into the sulcus on the facial surface but the dentist inadventently keeps the preparation at the same level on the interproximal surfaces as well. This procedure often disregards the parabolic architecture of the peridontal housing supporting the tooth and does considerable damage to the interproximal soft tissues. This damage is more often seen in the anterior region where the alveolus is narrow rather than in the posterior region where the alveolar process must be wide to accommodate the larger root surface (Figs. 5 and 6). During tooth preparation, regardless of the preparation design, it is critical that the dentist not injure the junctional epithelium or the connective tissue fiber apparatus, otherwise the gingival margin as well as the alveolar crest is likely to recede. If gingival recession can be avoided during the restorative phase, a major cosmetic problem may be avoided.
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RESTORATIONS
The provisional restoration is often neglected in fixed prosthodontics.i9 Its role with respect to periodontal health during fixed procedures is critically important. The provisional restoration often plays an important part in improving periodontal health prior to final preparation and in making the impression. Complex fixed restorations are often needed to replace old, worn, or inadequate restorations. The tissue changes that are seen around these defective restorations can frequently be reversed with well-fitting, properly contoured acrylic resin provisional restorations. If the damage to the periodontium is limited to the soft tissues, the effects usually are reversible once the provisional restorations are in place for a few weeks. The provisional restoration provides a matrix against which the tissue heals, guiding the generation of correct soft tissue architecture (Figs. 7 and 8). Even in patients with more severe periodontal disease, a well constructed provisional restoration can greatly improve soft tissue tone, thereby simplifying the ensuing periodontal procedures. Even though the patient with advanced periodontal disease usually requires osseous surgery to correct aberrant hard tissue architecture, a wellformed provisional restoration has the potential to greatly reduce inflammation, thereby simplifying the surgical procedures and speeding healing. During inital tooth preparation, it is important not to prepare the tooth to its full depth within the sulcus. Margins that are less invasive within the sulcus can be captured accurately when fabricating provisional restorations. This is essential to improve the soft tissue status at this time. An important requirement of the provisional restoration is that it have an accurate marginal seal. Without marginal seal, tissue health does not improve drastically. Proper form in the cervical portion of the provisional restoration is also needed for gingival health. The contour as it emerges from the sulcus is most often flat with no obvious bulge or height of contour. The form of the interproximal embrasure also greatly influences the ability of the soft tissue to resume its normal architecture. Embrasure spaces of the provisional restoration must be opened sufficiently to allow for interproximal cleansing with cleaning aids such as interproximal brushes or tufted dental floss. At this time, patients should be instructed in plaque removal around the provisional restorations. Provisional restorations are cemented with temporary cements that need to be sufficiently retentive to allow for normal function by the patient, while at the same time permitting removal by the dentist, if necessary. Failure to remove all traces of temporary cement from the sulcus or interproximal space negates much of the therapeutic potential of the provisional restoration. These irritants can result in inflammation of the marginal gingiva or interproximal papillae that will also se-
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verely compromise management.
IMPRESSION
efforts to maintain ideal soft tissue
PROCEDURES
Impression making of tooth preparations that extend subgingivally with an elastic material also has the potential for soft tissue abuse. Adequate gingival retraction is essential for predictable impression making. Although techniques for retraction have often been debated, the use of retraction cord has proved to be an effective method of soft tissue management during the impression phase. The placement of retraction cord and cotton strings into the gingival sulcus may cause injury to the sulcular epithelium.20 The damage inflicted to the soft tissue depends upon the chemical agent with which the cord has been impregnated, the force used in packing the cord, and the length of time the cord is left in place within the sulcus. The force used to place the cords should be minimal to avoid forcing the cord into the subepithelial connective tissue, Most importantly, prior to its removal, the cord should be moistened to avoid stripping the sulcular epithelium (Figs. 9 and 10). The placement of an intracrevicular bevel can be most helpful as a first step in gingival retraction. A bevel made with a fluted finishing bur or with a fine diamond creates a space, at the expense of the tooth surface not the inner tissue wall, which is adequate to accommodate retraction cord. Although the inner lining of the sulcular epithelium is usually abraded during the placement of the bevel, if no damage is inflicted to the underlying connective tissue healing takes place uneventfully, without recession. The removal of tooth structure in the placement of the intracrevicular bevel can be accomplished without premanent injury to the soft tissue. A widened sulcus can thus be obtained that is wide enough to accept retraction cord. In this manner the cord is placed rather than packed into the sulcus and gingival retraction procedures can be performed without causing permanent damage to the soft tissue (Figs. 11 through 13).
CROWN
CONTOUR
It is generally accepted that the “protective bulge” theory of human tooth contours is not compatible with current concepts of dental anatomy and periodontics.21 The belief that the purpose of facial and lingual enamel bulges of human teeth is to protect the marginal gingiva from the traumatic effects of mastication is no longer widely held. Now, it is universally accepted that the principal etiologic factor in both caries and periodontal disease is bacterial plaque. Therefore any tooth contour that promotes the retention of microbial plaque must be avoided. Overcontouring tends to encourage the retention of plaque and the ensuing development of inflammation. Conversely, the undercontoured tooth (enamel hyperplasia, cervical erosion, peg-shaped
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lateral incisor) rarely shows signs of gingival inflammation. Pere122 studied the relationship between axial tooth contours and the surrounding marginal gingiva in six dogs. He found that undercontouring did not produce any significant changes in gingival health, while overcontouring produced inflammatory and hyperplastic changes in the marginal tissues. For these reasons, the final restoration should follow the contour established by the root anatomy. The cervical third of the restoration should emerge from the gingival sulcus as flat as possible, especially in regions where it is difficult to maintain effective oral hygiene, such as fluted areas and furcated molars. An attempt should be made to flatten the facial and lingual contours of restorations to enable the most effective removal of plaque.
PONTIC
DESIGN
Stein23 has described the ideal pontic design as a “modified ridge lap” in the posterior region and a “lap facing” in the anterior region. He stated that the ideal tissue-contacting surface should be smooth and finely finished to offer a maximum level of cleansibility. No advantage seems to be served by using porcelain, acrylic resin, or gold as the tissue-contacting surface. What seems to be more important is the degree to which the tissue surface is polished. From a periodontal point of view, pontics represent oral hygiene problems for patients and therefore should be constructed to facilitate plaque removal. Ideally, there should be no contact or very slight contact between the tissue-contacting surface and the ridge mucosa, since histologic changes in the ridge tissues seem to be related to the amount of tissue covered by the pontic.24 As much as the shape of the residual ridge will allow, the tissue-contacting surface should be flat or convex, allowing for plaque removal by the passing of dental floss. Also, pontics should be the same length as the adjacent teeth. This can be achieved by shortening the gingival portion until the correct length is achieved. From a practical standpoint, pontic design must often be modified in favor of esthetics, either by covering more of the ridge surface or by creating an “ovate pontic design.“25 The pontic form that is chosen for a given situation should balance the factors of cleansibility and esthetics. In any case, the ridge tissue should be well keratinized, free of irregularities that would not permit adequate oral hygiene, and be in minimal contact with a highly polished surface (Fig. 14).
EMBRASURE
DESIGN
Embrasure contours might be more important than facial or lingual crown contours.26 The interproximal papilla responds rapidly to overcontouring of the embrasure region. It becomes inflamed and hypertrophied as a result of poor oral hygiene when the interproximal embrasure is impinged upon by overcontoured adjacent crown surfaces.
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Other factors may contribute to the papillary inflammatory often seen between splinted restorations. The papilla is likely to be inflamed because of the presence of subgingival margins on either side and is often constricted in an occlusal-gingival direction by the interproximal soldered connection. A study to determine whether there were embrasure dimensions that were more favorable to the health of the gingiva and underlying mucosa concluded that oral hygiene exerted a more important influence than the height of the embrasure.27 The ideal size of the interproximal embrasure is one that permits the introduction of cleaning aids for the removal of plaque in this most vital area (Fig. 15). Embrasures that are excessively opened impact negatively upon esthetics, impair phonetics, and allow excessive lateral food impaction. The patient with normal clinical crown length often presents a dilemma when one is designing an ideal embrasure form. Interproximal height is often not sufficient to allow space for an interproximal brush without weakening the interproximal connector. Tufted dental floss can be used in these situations, especially for anterior teeth (Fig. 16). The patient with advanced periodontal disease usually presents much more interproximal height, and in some instances, has so much apical migration of the attachment apparatus that the embrasure space is excessively wide, which leads to esthetic, phonetic, and food impaction problems. This predicament can be further complicated by root proximity problems, cervical concavities, and root anatomy irregularities. Correct embrasure form often requires a balancing of all the factors mentioned.
LONG-TERM
MAINTENANCE
The trauma to the periodontal apparatus caused by tooth preparation, provisional restorations, gingival retraction, and impression procedures is often reversible. In addition to the design of the restoration, the marginal adaptation is likely to affect the peridontal structures on a permanent basis. The subgingival area (the crown margin, the luting agent, and the prepared tooth) often accounts for the destructive effects on the soft tissue frequently seen adjacent to subgingival restorations. This area tends to be a refuge for bacteria and necrotic tissue. Several sources of surface roughness can exist in this subgingival area. From a periodontal point of view, all restorative margins are ill-fitting and rough. Even carefully polished surfaces and exact margins are irregular when examined microscopically. In addition, the luting agents used for cementation tend to be porous and leave a very rough surface to which microbial products may adhere. These rough surfaces are like calculus in that they are continuously coated with bacterial plaque and are responsible for an ever-deepening sulcus. Unlike calculus, however, ill-fitting margins cannot be easily removed and they represent a much greater problem for the periodontist.
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After cementation, all remnants of excess cement must be removed. In addition, the junction of the crown margin and the tooth finishing line, an area filled with cement, should be smoothed as much as possible with curettes to reduce the roughness of the luting agent. Roughness at the interface of tooth and restoration cannot be totally eliminated, but if the restoration is properly fabricated and finished, the slight remaining roughness can be well tolerated by the soft tissues. Long-term stability of the intricate relationship between the restoration and the periodontal structures requires the active involvement of the patient and the dentist. Once the restoration has been constructed with adherence to all the factors governing the achievement of optimal soft tissue health and is placed into this healthy environment, a strict maintenance regimen can ensure its survival. Adequate plaque removal by a well motivated patient, as well as careful maintenance visits, are essential for the preservation of this delicate state of coexistence between the soft tissue and the restoration. With effective plaque control, routine scaling, follow-up radiographs, and a careful evaluation of sulcular health at regular intervals, it is realistic to expect the soft tissue architecture to remain quite stable for a long period of time.
REFERENCES
7. Larato DC. The effect of crown margin extension to gingival inflammation. J South Calif Dent Assoc 196%37:476-l+. 8. Silness J. Periodontal conditions in patients treated with dental bridges. J Periodont Res 1970;5:219-24. Acta Odontol 9. Karlsen K. Gingival reactions to dental restorations. Stand 1970;28:895-904. 10. Newcomb GM. The relationship between the location of subgingival crown margins and gingival inflammation. J Periodontol1974;45:151-4. 11. Silness J. Fixed prosthodontics and periodontal health. Dent Clin North Am 1980;24:317-29. 12. Richter WA, Ueno H. Relationship of crown margin placement to gingival inflammation. J PROSTHET DENT 1973;30:156-61. 13. Crispin BJ, Watson JF. Margin placement of esthetic veneer crowns. Part 1. Anterior tooth visibility. J PROSTHET DENT 1981;45:278-82. 14. Crispin BJ, Watson JF. Margin placement of esthetic veneer crowns. Part II. Posterior tooth visibility. J PROSTHET DENT 1981;45:389-91. 15. Watson JR, Crispin BJ. Margin placement of esthetic veneer crowns. Part III. Attitudes of patients and dentists. J PROSTHET DENT 1981; 45:499-501.
16. Valderhaug J, Birkeland JM. Periodontal conditions in patients 5 years following insertion of fixed prostheses. J Oral Rehabil 1976;3:237-43. 17. Nevins M, Skurow HN. The intracervicular restorative margin, the biologic width, and the maintenance of the gingival margin. Int J Peridontol Restor Dent 1984;3:31-49. 18. Liie H. Reactions of marginal tissues to restorative procedures. Int Dent J 196818759-78. 19. Shave11 HM. Mastering the art of tissue management during provisionalization and biologic final impressions. Int J Periodonto Restor Dent 1988325-43. 20. Liie H. Silness J. Tissue reactions to string packs used in fixed restorations. J PROSTHET DENT 1963;13:318-23. 21. Yuodelis RA, Weaver JD, Sapkos S. Facial and lingual contours of artificial complete crown restorations and their effects on the periodontium. J PROSTHET DENT 1973;29:61-6. 22. Perel ML. Axial crown contours. J PROSTHET DENT 1971;25:642-9. 23. Stein RS. Pontic-residual ridge relationship: a research report. J PROSTHET DENT
1. Stein RS. Glickman I. Periodontal considerations essential for gingival health. Dent Clin North Am 1960;4:177-88. 2. Shave11 HM. Mastering the art of tissue management and biologic final impressions. Int J Periodontal Res Dent 1988;3:25-43. 3. Nemetz H. Tissue management in fixed prosthodontics. J PROSTHET DENT
1974;31:628-36.
4. Wagman
SS. Tissue management
THET DENT
DENT
for full cast veneer crowns. J PROS-
1965;15:106-17.
5. Waerhaug J. Histologic considerations which govern where the margins of restorations should be located in relation to the gingiva. Dent Clin North Am 1960;4:161-76. 6. Marcum JS. The effect of crown margin depth upon gingival tissue. J PROSTHET DENT 1967;17:479-87.
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1966;16:251-85.
24. Henry PJ, Johnston JF, Mitchell DF. Tissue changes beneath fixed partial dentures. J PROSTHET DENT 1966$6:937-47. 25. Garber DA. The edentulous ridge in fixed prosthodontics. Compend Contin Ed 1981;II:212-24. 26. Morris ML. Artificial crown contours and gingival health. J PROSTHET 1962;12:1146-56.
27. Hirshberg SM. The relationship of oral hygiene to embrasure and pontic design-a preliminary study. J PROSTHET DENT 1972;27:26-38. Reprint
requests to:
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