EVALUATION
OF RESISTANCE
FORM
studies are needed to confirm the extent to which lack of resistance form is present in castings that fail by dislodgment.
1. Potts RG, Shiiliugburg HT, Duncanson ME. Retention and resistance of preparations for cast restorations. J PROSTHET DENT 1980;43:303-8. 2. Woolsey GD, Matich JA. The effect of axial grooves on the resistance
form of cast restorations. J A m Dent Aesoc 1978;97:978-80.
CONCLUSIONS 1. The resistance form of 294 preparations was evaluated. 2. Ninety-six percent of incisors, 92 % of canines, 81% of premolars, and 46% of molars were shown to have resistance form. 3. None of the anterior teeth had grooves. Only one of 72 premolars and eight of 107 molars (7%) had grooves. 4. Although a statistically significant sample was not available, grooves appeared to improve resistance form in molars, with mesial or distal grooves providing resistance form to buccal and lingual dislodgment, and buccal or lingual grooves providing resistance form to mesial and distal dislodgment.
Restorative William
REFERENCES
margin
G. Reeves,
The University
placement
3. Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of fixed prosthodontics. 1st ed. Berlin: Buch-und-Zeitschriften-Verlag “Die Quin-
tessenz,” 1976:85. 4. Lewis RM, Owen MM. A mathematical solution of a problem in full
crown construction. J A m Dent Assoc 1959;59:943-7. 5. Weed RM, Baez RJ. A method for determining adequate resistance form of complete cast crown preparations. J PROSTHET DENT 1984; 52330-4. 6. Parker MH, Gunderson RB, Gardner FM, Calverley MJ. Quantitative
determination of taper adequate to provide resistance form: concept of limiting taper. J PROSTHET DENT 1968;59:281-8 7. Kaufman EG, Coelho DH, Colin L. Factors influencing the retention of cemented gold castings. J PROSTHET DENT 1961;11:487-502.
Reprintrequeststo: DR. MERLE HARRY PARKER 7138 CLIPPER RIDGE CONVERSE, TX 78109
and periodontal
health
DDSa
of Oklahoma,
College of Dentistry
Oklahoma City, Okla.
Subgingival restorative margins are associated with the development of plaquerelated inflammatory periodontal disease, primarily because of a shift in the subgingival microflora from a profile associated with health to one associated with disease. The degree and extent of the marginal inflammation is influenced by four factors: failure to maintain proper emergence profile, inability to adequately finish and/or close subgingival margins, placement of subgingival margins in an area with minimum to no attached gingiva, and violation of the biologic width. Supragingival margin placement is the location of choice for all restorative margins to avoid iatrogenic periodontal disease. However, consideration of these four factors will help reduce the adverse impact of restorative margins that must be carried subgingivally. (J PROSTHETDENT 1991;66:733-6.)
L oss of
periodontal attachment as a result of plaque-related inflammatory periodontal disease is a major cause of tooth loss in the adult popu1ation.l Although the exact mechanism of periodontal attachment loss is not completely understood, there is ample evidence that destruction of the periodontal attachment apparatus is preceded by inflammatory changes in the marginal gingiva.2 The primary cause of these inflammatory changes is microbial plaque.3 However, subgingival restorative margins
%linical Associate Professor, Department 10/l/29631
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
of Periodontics.
are also a major contributing factor.4 Although much has been written regarding this subject, there still appears to be controversy regarding the placement of restorative margins. This article reviews how subgingivally located restorative margins may adversly affect periodontal health and discusses guidelines designed to help the dentist prevent iatrogenic periodontal disease when completing restorative procedures. Cross-sectional and longitudinal studies alike have shown that placement of restorative margins subgingivally may result in the development of iatrogenic marginal inflammation.5W22Although there have been isolated reports of
733
REEVES
metal allergies”” and reactions to dental cements,24ls5 the infiammatory changes associated with subgingival margin placement are generally not a reaction to the dental materia1s.s” Direct tissue irritation from subgingival restorative margins has also been ruled out as a primary cause of marginal inflammation.27 Most current research points out that the subgingival margin creates a protected area that encourages more rapid plaque accumulation and is inaccessible for effective oral hygiene.s* The result is a shift in the subgingival microflora from a profile compatible with health to a profile with the potential to cause periodontal destruction.22, 2g At least four factors appear to affect adversely the degree and extent, of the inflammatory changes that are associated with subgingival margin placement. These factors include failure to maintain proper emergence profile, inability to adequately finish or close subgingival margins, placement of subgingival margins in an area with minimum to no attached gingiva, and violation of the biologic width. EMERGENCE
PROFILE
Failure to maintain proper emergence profile30 may be a result of relying on the theory of food deflection when developing crown contours, or it may be a result of failure to remove adequate tooth structure during tooth preparation. The food deflection theory advocated overbulking the gingival third of the restoration to act as a deflective contour to protect the gingival tissue from injury.“’ Lack of adequate reduction during tooth preparation for complete or partial coverage will necessitate overbulking the final restoration at the gingival margin for adequate material strength.32 This is particularly true with the porcelain-veneered metal crown that extends onto the root surface where the tooth profile is relatively vertical. In either case, if the restorative margin is extended subgingivally, these overbulked contours change the emergence profile of the tooth. This will create a protected area that encourages plaque accumulation and is more difficult to clean. Teeth with overcontoured restorations will develop marginal inflammation whereas contralateral teeth that have not been restored will remain healthy.33-35Careful attention to developing the proper emergence profile in the final restoration will help reduce plaque retentive areas and will thus reduce iatrogenic inflammation. IMPROPERLY
FINISHED
MARGINS
The second factor that contributes to gingival inflammation when a restoration is extended subgingivally is the improperly finished margin. Whether it is a direct or indirect technique, a margin placed subgingivally is difficult to finish and will inevitably be a plaque-retentive area. Christensen3” found that in an ideal environment the acceptable mean opening of subgingivally placed margins of cast restorations that were not visually accessible was almost 3.5 times the acceptable mean opening of supragingival margins that were visually accessible.
731
In most cases, overhangs or large open margins are probably left because of the inability of the clinician to obtain an adequate impression and/or properly finish the margin when the restoration is completed in a subgingival location. The deeper the margin is extended subgingivally, the less likely will the margin be properly finished. Open margins and overhangs associated with subgingival margins are protected areas where large numbers of pathologic organisms accumulate. Access to these areas for effective oral hygiene is extremely limited, and thus they are generally associated with a chronic inflammatory response and greater attachment 10ss.~~-~~ Care in impression making and in finishing the restoration will help reduce open margins and overhangs. However, any subgingivally located margin has the potential to be less ideal than a supragingivally located margin. INADEQUATE
ZONE
OF GINGIVA
A third factor that may contribute to marginal inflammation associated with subgingivally placed restorative margins is the lack of an adequate band of firmly bound or attached gingiva. Many patients have marginal gingiva that is described as thin and scalloped,40 or they may have marginal tissue that consists purely of mucosal tissue. In either case, the tissue is thin and delicate and may be more susceptable to injury than marginal tissue that consists primarily of a wide band of dense attached gingiva. Even though it is well documented that thin marginal tissue can be maintained in a state of health over a long period of time,41, 42 introduction of a restorative margin subgingivally with this type of tissue will have an adverse impact on periodontal health. The result will be a significant amount of marginal inflammation, followed by subsequent attachment loss and gingival recession.43 At this time there is limited information regarding the minimum width of attached gingiva that should be present to minimize the adverse impact of a subgingivally placed restorative margin. Maynard and W ilson suggested that a band of attached gingiva at least 3 m m wide should be present before subgingival margin placement is considered.44However, there is little research to support this recommendation. In any event, in patients with little or no attached gingiva, subgingival restorative margins are contraindicated without a preliminary gingival augmentation procedure. VIOLATION
OF THE
BIOLOGIC
W IDTH
Violation of the biologic width is the fourth factor that contributes to the inflammatory reaction when a margin is placed subgingivally.45 The biologic width consists of attached epithelial cells (junctional epithelium) and connective tissue attachment (dentogingival fibers embedded in cementum). These two zones form a biologic seal around the neck of the tooth that acts as a barrier to help prevent migration of microorganisms and their products into the underlying gingival connective tissue and supporting alve-
DECEMBER
1991
VOLUME
66
NUMBER
6
RESTORATIVE
MARGIN
PLACEMENT
olar bone. Each zone is approximately 1 m m wide46 and together they extend from the base of the gingival crevice to the osseous crest. Technically, a restorative margin can be extended to the base of the gingival crevice (as long as the contours are contained within the confines of the original tooth profile and the margin is well finished) without undue sequelae. However, extension apical to the base of the histologic crevice will violate the biologic width and will disrupt the biologic seal. This extension will allow bacteria and their products to penetrate the underlying connective tissue with resultant inflammation. The result is loss of connective tissue attachment and apical migration of the marginal attachment apparatus. This pathologic remodeling may occur as rapidly as 2 weeks after placement of the subgingival margin.47 Unfortunately, determining the histologic base of the gingival crevice and the coronal border of the biologic width is not possible clinically. If the marginal gingiva has been brought to a state of optimum health, the histologic crevice depth is probably slightly more than 0.5 m m deep.46The crevice depth measured by clinical probing will always be deeper than the histologic crevice depth because of the limited resistence of the junctional epithelium to even light probing forces. 48As marginal inflammation develops, probe tip penetration increases as the result of a decrease in epithelial cell adhesion and loss of collagen fibers in the gingival connective tissue. 4g,50 Thus, clinical probing depths cannot accurately determine the base of the gingival crevice and the coronal border of the biologic width, particularly in the presence of a preexisting marginal inflammation. Current standards of care dictate that the gingiva should be brought to a state of health before any restorative procedure is initiated. Once a healthy gingival environment has been established, the best rule is to assume that any margin placed more than 0.5 m m subgingivally will violate the biologic width and will result in an inflammatory marginal lesion that will eventually lead to marginal attachment loss. CONCLUSION Placement of restorative margins subgingivally generally results in the development of an iatrogenic marginal inflammation. A recent study indicated that even when crown margins are placed level with the gingival margin, the clinical and microbiologic parameters of periodontal health will be significantly worse than with margins in the supragingival location. Indeed, some of the parameters for the marginal location did not differ significantly from the subgingivally located margin.22 A poorly fitted and contoured restorative margin is unacceptable at any position, but even a perfectly fitted and contoured margin that extends more than 0.5 m m below the marginal gingiva in a healthy environment will violate the biologic width and will result in a marginal inflamma-
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
tion, particularly if there is little to no attached gingiva present. The more supragingivally a restorative margin can be placed, the less chance that the margin will contribute to gingival inflammation. In addition, a supragingival margin can be finished better and can be more easily evaluated for recurrent caries or marginal deterioration at periodic supportive maintenance recall visits. If a restorative margin must be extended below the gingival margin, it is critical that (1) proper emergence profile is maintained, (2) the margin is closed and properly finished, (3) an adequate band of attached gingiva is present, and (4) the margin does not violate the biologic width. If these criteria are followed, the impact of the subgingivally located restorative margin will be significantly reduced. REFERENCES 1. American Dental Association, Bureau of Economic Research and Statistics Survey of needs for dental care. 1965, II Dental needs according to age and sex of patients. J A m Dent Assoc 1965;73:1355-65. 2. Kornman K. The role of supragingival plaquein the preventionand treatment of periodontal diseases.J Periodont Res, 1986 Suppl16;21:522. 3. Slots J. Suhgingival microflora and periodontal disease. J Clin Periodonto1 1979;6:351-82. 4. Sheiham A. Prevention and control of periodontal disease: International Conference in Research in the Biology of Periodontal Disease. Urbana: University of Illinois, 1977;336. 5. Trivedi SC, Talim ST. The response of human gingiva to restorative materials. J PROSTHETDENT 19’73;29:73-80. 6. L6e H. Reactions of marginal periodontal tissues to restorative procedures. Int Dent J 1986;18:759-78. I. Arneberg P, Silness J, Nordbo H. Marginal fit and cervical extent of Class II amalgam restorations related to periodontal conditions. J Periodont Res 1980;15:669-77. 8. Gorse I, Newman HN, Strahan JD. Amalgam restorations, plaque removal and periodontal health. J Clin Periodontol 1979;6:98-105. 9. Mormann W , Regolati B, Renggli HH. Gingival reaction to well-fitted subgingival proximal gold inlays. J Clin Periodontol 1974;1:120-5. 10. Orkin DA, Reddy J, Bradshaw D. The relationship of the position of crown margins to gingival health. J PROSTHETDENT 1987;57:421-4. 11. SilnessJ. Fixed prosthodontics and periodontal health. Dent Clin North A m 1980;24:317-29. 12. SilnessJ. Periodontal conditions in patients treated with dental bridges. J Periodont Res 1970;5:60-8. 13. Silness J. Periodontal conditions in patients treated with dental bridges. Part II. J Periodont Res 1970;5:219-24. 14. SilnessJ. Periodontal conditions in patients treated with dental bridges. Part III. J Periodont Res 1970;5:225-9. 15. Renggli HH, Rengolati B. Gingival inflammation and plaque accumulation by well-adapted supragingival and subgingival proximal restoration. Helv Odontol Acta 1972;16:99-101. 16. Karlsen K. Gingival reactions to dental restorations. Acta Odontol Stand 1970;28:895-904. 17. Richter W , Ueno H. Relationship of crown margin placement to gingival inflammation. J PROSTHETDENT 1973;30:156-61. 18 Muller HP. The effect of artificial crown margins at the gingival margin on the periodontal conditions in a group of periodontally supervised patients treated with fixed bridges. J Clii Periodontol1986;13:97-102. 19. Bergman B, Hugson A, Olson CO. Periodontal and prosthetic conditions in patients treated with removable partial dentures and artificial crowns. Acta Odontol Stand 1971;29:621-38. 20. Valderhaug J, Birkeland JM. Periodontal conditions in patient five years following insertion of fixed prostheses. J Oral Rehabil1976;3:23743. 21. Newcomb G. The relationship between the location of subgingival crown margins and inflammation. J Periodontol 1974;45:151-4.
135
22. Fkm+bk&y
L, &@og+os
&rg$$ foo(it;loli @..ueand !&or Dent’ w-206. 23.
24. 25. 26. 27.
Gf2, Cimcio S. The effect of cmwn periodontal
health. Int J Pericdont
Re-
%#@a~,~~-~~l~~~
of niekle based dental alloys. CDAJ 1984; 1245-51. ZwderHA; E&et of silicate cement and amalgam on the gingiva. J Am Dent Asaoe~196~;65:11-5. Waerhaag J.-&$Xectofzinc phosphate cement fillings on gingival tissues. J P&&n&l l&%$7:284-91. Leon AR. The periodontium and restorative procedures. A critical review. J Oral R&tbil 1977;4:104-7. Waerhaugh J. Effect of rough surfaces upon gingival tissue. J Dent Res
1%6;35:823-5. 28. Sotres LS, Van Huysen G, Gilmore HW. A histologic study of gingival
$i&uerespCnse to amalgam, silicate, and resin restorations. J Periodonto1 1969;4&548-6. 29. Lang NP,Kiel -$U, Anderbalden K. Clinical and microbiological effects of ~~~~~~ions with overhanging or clinically perfect margips. J f.?l.&Pericdontol 1983;10:563-78. 30. St.& RE; Kuwata M. A dentist and a dental technologist analyze current cermo-metal procedures. Dent Clin North Am 1977;21:729-49. 31. Wheeler RC. Complete crown form and the periodontium. J PROSTHET DENT 1961;11:722-34.
32. W&gold AS. Tooth preparation in fixed prosthesis (Part I). Compend Co&n Educ Dent 1980;6:375-83. 33. Perel I&& k&l
c’own contours.
J PROSTHET DENT 1971;25:642-9.
34. P&iitin~CO. E&es&e crown contours facilitate endemic plaque nicl+s. J Pwnr DENT 197%35:424-g. 35. Yimdelk RA, Weaver JD, Sapkos S. Facial and lingual contours of artificial compl& crown restorations and their effects on the periodontium. J PROSTFSET DENT 1972;29:61-6. 36. Ghriste&sen GJ. Marginal fit of gold inlay castings. J PROSTHET DENT i9tqm297m5. 37. Ke&he$i G, &abo I. Intluence of class II amalgam fillings on attachment loss. J Clin Periodontol 19&L;11:81-6. 38. I-%kkarainen K, Ainamo J. Influence of overhanging posterior tooth restorations on alveolar bone height in adults. J Clin Periodontol I980;7:114-20.
1 I
i I i
Bound
volumes
available
39. Jeffcoat MK, Howell TH. Alveolar bone destruction due to overhanging amalgam in periodontal disease. J Periodontal 1984)$X:599-602. 40. Ochsenbeen C, Ross S. A concept of osseous surgery and its clinical application. Chap 13 In: Ward HL, ed. A periodontal point of vieur Springfield, Ill; Charles C. Thomas, Publ, 1973. 41. Wennstrom J, Lindhe J. Role of attached gingiva for maintenance of periodontal health. J Clin Periodontol 1983;10:206-21. 42. Dorfman HS, Kennedy JE, Bird WC. Longitudinal evaluation of free autogenous gingival grafts. J Clin Periodontol 1980;7:316-24. 43. Ericsson I, Lindhe J. Recession in sites with inadequate width of the keratinized gingiva. An experimental study in the dog. J Clin Periodonto1 1984;11:95-103. 44. Maynard JG, Wilson RD. Physiologic dimensions of the periodontium significant to the restorative dentist. J Periodontol 1979;50:170-4. 45. Ingber JS, Rose LF, Coslet JG. The “biologic width”-a concept in periodontics and restorative dentistry. Alpha Omegan 1977;70:62-5. 46. Gargiuilo AW, Wentz FM, Orban B. Dimensions and relations of the dentogingival junction in humans. J Periodontol 1961;32:261-7. 47. Tarnow D, Stab1 SS, Magner A, Zamzok J. Human gingival attachment responses to subgingival crown placement. Marginal remodelling. J Clin Periodontol 1986;13:563-9. 48. Listgarten MA. Periodontal probing: what does it mean? J Clin Periodonto1 1980;7:165-76. 49. Armitage GC, Svanberg GK, L6e H. Microscopic evaluation of clinical measurements of connective tissue attachment levels. J Clin Periodonto1 1977;4:173-90. 50. Saglie R, Johansen JR, Flotra L. The zone of completely and partially destructed periodontal fibers in pathologic pockets. J Clin Periodontol 1975;2:198-202. Reprint requests to: DR. WILLIAM G. REEVES COLLEGEOFDENTISTRY UNIVERSITY OF OKLAHOMA P.O.Box 26901 ~OO~STANTONL.YOUNG BLVD. OKLAHOMA CITY,OK 73190
to subscribers
Bound volumes of THE JOURNAL OF PROSTHETIC DENTISTRY are available to subscribers (only) for the 1991 issues from the publisher at a cost of $50.00 ($63.00 international) for Vol. 65 (January-June) and Vol. 66 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 63 and 64 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800) 325-4177, ext. 4351. Subscriptions must be in force to quakfy. Bound volumes are not available in place of a regular JOURNAL subscription.
DECEMBER
1991
VOLUME
66
NUMBER
6
OF RESISTANCE
FORM
studies are needed to confirm the extent to which lack of resistance form is present in castings that fail by dislodgment.
1. Potts RG, Shiiliugburg HT, Duncanson ME. Retention and resistance of preparations for cast restorations. J PROSTHET DENT 1980;43:303-8. 2. Woolsey GD, Matich JA. The effect of axial grooves on the resistance
form of cast restorations. J A m Dent Aesoc 1978;97:978-80.
CONCLUSIONS 1. The resistance form of 294 preparations was evaluated. 2. Ninety-six percent of incisors, 92 % of canines, 81% of premolars, and 46% of molars were shown to have resistance form. 3. None of the anterior teeth had grooves. Only one of 72 premolars and eight of 107 molars (7%) had grooves. 4. Although a statistically significant sample was not available, grooves appeared to improve resistance form in molars, with mesial or distal grooves providing resistance form to buccal and lingual dislodgment, and buccal or lingual grooves providing resistance form to mesial and distal dislodgment.
Restorative William
REFERENCES
margin
G. Reeves,
The University
placement
3. Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of fixed prosthodontics. 1st ed. Berlin: Buch-und-Zeitschriften-Verlag “Die Quin-
tessenz,” 1976:85. 4. Lewis RM, Owen MM. A mathematical solution of a problem in full
crown construction. J A m Dent Assoc 1959;59:943-7. 5. Weed RM, Baez RJ. A method for determining adequate resistance form of complete cast crown preparations. J PROSTHET DENT 1984; 52330-4. 6. Parker MH, Gunderson RB, Gardner FM, Calverley MJ. Quantitative
determination of taper adequate to provide resistance form: concept of limiting taper. J PROSTHET DENT 1968;59:281-8 7. Kaufman EG, Coelho DH, Colin L. Factors influencing the retention of cemented gold castings. J PROSTHET DENT 1961;11:487-502.
Reprintrequeststo: DR. MERLE HARRY PARKER 7138 CLIPPER RIDGE CONVERSE, TX 78109
and periodontal
health
DDSa
of Oklahoma,
College of Dentistry
Oklahoma City, Okla.
Subgingival restorative margins are associated with the development of plaquerelated inflammatory periodontal disease, primarily because of a shift in the subgingival microflora from a profile associated with health to one associated with disease. The degree and extent of the marginal inflammation is influenced by four factors: failure to maintain proper emergence profile, inability to adequately finish and/or close subgingival margins, placement of subgingival margins in an area with minimum to no attached gingiva, and violation of the biologic width. Supragingival margin placement is the location of choice for all restorative margins to avoid iatrogenic periodontal disease. However, consideration of these four factors will help reduce the adverse impact of restorative margins that must be carried subgingivally. (J PROSTHETDENT 1991;66:733-6.)
L oss of
periodontal attachment as a result of plaque-related inflammatory periodontal disease is a major cause of tooth loss in the adult popu1ation.l Although the exact mechanism of periodontal attachment loss is not completely understood, there is ample evidence that destruction of the periodontal attachment apparatus is preceded by inflammatory changes in the marginal gingiva.2 The primary cause of these inflammatory changes is microbial plaque.3 However, subgingival restorative margins
%linical Associate Professor, Department 10/l/29631
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
of Periodontics.
are also a major contributing factor.4 Although much has been written regarding this subject, there still appears to be controversy regarding the placement of restorative margins. This article reviews how subgingivally located restorative margins may adversly affect periodontal health and discusses guidelines designed to help the dentist prevent iatrogenic periodontal disease when completing restorative procedures. Cross-sectional and longitudinal studies alike have shown that placement of restorative margins subgingivally may result in the development of iatrogenic marginal inflammation.5W22Although there have been isolated reports of
733
REEVES
metal allergies”” and reactions to dental cements,24ls5 the infiammatory changes associated with subgingival margin placement are generally not a reaction to the dental materia1s.s” Direct tissue irritation from subgingival restorative margins has also been ruled out as a primary cause of marginal inflammation.27 Most current research points out that the subgingival margin creates a protected area that encourages more rapid plaque accumulation and is inaccessible for effective oral hygiene.s* The result is a shift in the subgingival microflora from a profile compatible with health to a profile with the potential to cause periodontal destruction.22, 2g At least four factors appear to affect adversely the degree and extent, of the inflammatory changes that are associated with subgingival margin placement. These factors include failure to maintain proper emergence profile, inability to adequately finish or close subgingival margins, placement of subgingival margins in an area with minimum to no attached gingiva, and violation of the biologic width. EMERGENCE
PROFILE
Failure to maintain proper emergence profile30 may be a result of relying on the theory of food deflection when developing crown contours, or it may be a result of failure to remove adequate tooth structure during tooth preparation. The food deflection theory advocated overbulking the gingival third of the restoration to act as a deflective contour to protect the gingival tissue from injury.“’ Lack of adequate reduction during tooth preparation for complete or partial coverage will necessitate overbulking the final restoration at the gingival margin for adequate material strength.32 This is particularly true with the porcelain-veneered metal crown that extends onto the root surface where the tooth profile is relatively vertical. In either case, if the restorative margin is extended subgingivally, these overbulked contours change the emergence profile of the tooth. This will create a protected area that encourages plaque accumulation and is more difficult to clean. Teeth with overcontoured restorations will develop marginal inflammation whereas contralateral teeth that have not been restored will remain healthy.33-35Careful attention to developing the proper emergence profile in the final restoration will help reduce plaque retentive areas and will thus reduce iatrogenic inflammation. IMPROPERLY
FINISHED
MARGINS
The second factor that contributes to gingival inflammation when a restoration is extended subgingivally is the improperly finished margin. Whether it is a direct or indirect technique, a margin placed subgingivally is difficult to finish and will inevitably be a plaque-retentive area. Christensen3” found that in an ideal environment the acceptable mean opening of subgingivally placed margins of cast restorations that were not visually accessible was almost 3.5 times the acceptable mean opening of supragingival margins that were visually accessible.
731
In most cases, overhangs or large open margins are probably left because of the inability of the clinician to obtain an adequate impression and/or properly finish the margin when the restoration is completed in a subgingival location. The deeper the margin is extended subgingivally, the less likely will the margin be properly finished. Open margins and overhangs associated with subgingival margins are protected areas where large numbers of pathologic organisms accumulate. Access to these areas for effective oral hygiene is extremely limited, and thus they are generally associated with a chronic inflammatory response and greater attachment 10ss.~~-~~ Care in impression making and in finishing the restoration will help reduce open margins and overhangs. However, any subgingivally located margin has the potential to be less ideal than a supragingivally located margin. INADEQUATE
ZONE
OF GINGIVA
A third factor that may contribute to marginal inflammation associated with subgingivally placed restorative margins is the lack of an adequate band of firmly bound or attached gingiva. Many patients have marginal gingiva that is described as thin and scalloped,40 or they may have marginal tissue that consists purely of mucosal tissue. In either case, the tissue is thin and delicate and may be more susceptable to injury than marginal tissue that consists primarily of a wide band of dense attached gingiva. Even though it is well documented that thin marginal tissue can be maintained in a state of health over a long period of time,41, 42 introduction of a restorative margin subgingivally with this type of tissue will have an adverse impact on periodontal health. The result will be a significant amount of marginal inflammation, followed by subsequent attachment loss and gingival recession.43 At this time there is limited information regarding the minimum width of attached gingiva that should be present to minimize the adverse impact of a subgingivally placed restorative margin. Maynard and W ilson suggested that a band of attached gingiva at least 3 m m wide should be present before subgingival margin placement is considered.44However, there is little research to support this recommendation. In any event, in patients with little or no attached gingiva, subgingival restorative margins are contraindicated without a preliminary gingival augmentation procedure. VIOLATION
OF THE
BIOLOGIC
W IDTH
Violation of the biologic width is the fourth factor that contributes to the inflammatory reaction when a margin is placed subgingivally.45 The biologic width consists of attached epithelial cells (junctional epithelium) and connective tissue attachment (dentogingival fibers embedded in cementum). These two zones form a biologic seal around the neck of the tooth that acts as a barrier to help prevent migration of microorganisms and their products into the underlying gingival connective tissue and supporting alve-
DECEMBER
1991
VOLUME
66
NUMBER
6
RESTORATIVE
MARGIN
PLACEMENT
olar bone. Each zone is approximately 1 m m wide46 and together they extend from the base of the gingival crevice to the osseous crest. Technically, a restorative margin can be extended to the base of the gingival crevice (as long as the contours are contained within the confines of the original tooth profile and the margin is well finished) without undue sequelae. However, extension apical to the base of the histologic crevice will violate the biologic width and will disrupt the biologic seal. This extension will allow bacteria and their products to penetrate the underlying connective tissue with resultant inflammation. The result is loss of connective tissue attachment and apical migration of the marginal attachment apparatus. This pathologic remodeling may occur as rapidly as 2 weeks after placement of the subgingival margin.47 Unfortunately, determining the histologic base of the gingival crevice and the coronal border of the biologic width is not possible clinically. If the marginal gingiva has been brought to a state of optimum health, the histologic crevice depth is probably slightly more than 0.5 m m deep.46The crevice depth measured by clinical probing will always be deeper than the histologic crevice depth because of the limited resistence of the junctional epithelium to even light probing forces. 48As marginal inflammation develops, probe tip penetration increases as the result of a decrease in epithelial cell adhesion and loss of collagen fibers in the gingival connective tissue. 4g,50 Thus, clinical probing depths cannot accurately determine the base of the gingival crevice and the coronal border of the biologic width, particularly in the presence of a preexisting marginal inflammation. Current standards of care dictate that the gingiva should be brought to a state of health before any restorative procedure is initiated. Once a healthy gingival environment has been established, the best rule is to assume that any margin placed more than 0.5 m m subgingivally will violate the biologic width and will result in an inflammatory marginal lesion that will eventually lead to marginal attachment loss. CONCLUSION Placement of restorative margins subgingivally generally results in the development of an iatrogenic marginal inflammation. A recent study indicated that even when crown margins are placed level with the gingival margin, the clinical and microbiologic parameters of periodontal health will be significantly worse than with margins in the supragingival location. Indeed, some of the parameters for the marginal location did not differ significantly from the subgingivally located margin.22 A poorly fitted and contoured restorative margin is unacceptable at any position, but even a perfectly fitted and contoured margin that extends more than 0.5 m m below the marginal gingiva in a healthy environment will violate the biologic width and will result in a marginal inflamma-
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
tion, particularly if there is little to no attached gingiva present. The more supragingivally a restorative margin can be placed, the less chance that the margin will contribute to gingival inflammation. In addition, a supragingival margin can be finished better and can be more easily evaluated for recurrent caries or marginal deterioration at periodic supportive maintenance recall visits. If a restorative margin must be extended below the gingival margin, it is critical that (1) proper emergence profile is maintained, (2) the margin is closed and properly finished, (3) an adequate band of attached gingiva is present, and (4) the margin does not violate the biologic width. If these criteria are followed, the impact of the subgingivally located restorative margin will be significantly reduced. REFERENCES 1. American Dental Association, Bureau of Economic Research and Statistics Survey of needs for dental care. 1965, II Dental needs according to age and sex of patients. J A m Dent Assoc 1965;73:1355-65. 2. Kornman K. The role of supragingival plaquein the preventionand treatment of periodontal diseases.J Periodont Res, 1986 Suppl16;21:522. 3. Slots J. Suhgingival microflora and periodontal disease. J Clin Periodonto1 1979;6:351-82. 4. Sheiham A. Prevention and control of periodontal disease: International Conference in Research in the Biology of Periodontal Disease. Urbana: University of Illinois, 1977;336. 5. Trivedi SC, Talim ST. The response of human gingiva to restorative materials. J PROSTHETDENT 19’73;29:73-80. 6. L6e H. Reactions of marginal periodontal tissues to restorative procedures. Int Dent J 1986;18:759-78. I. Arneberg P, Silness J, Nordbo H. Marginal fit and cervical extent of Class II amalgam restorations related to periodontal conditions. J Periodont Res 1980;15:669-77. 8. Gorse I, Newman HN, Strahan JD. Amalgam restorations, plaque removal and periodontal health. J Clin Periodontol 1979;6:98-105. 9. Mormann W , Regolati B, Renggli HH. Gingival reaction to well-fitted subgingival proximal gold inlays. J Clin Periodontol 1974;1:120-5. 10. Orkin DA, Reddy J, Bradshaw D. The relationship of the position of crown margins to gingival health. J PROSTHETDENT 1987;57:421-4. 11. SilnessJ. Fixed prosthodontics and periodontal health. Dent Clin North A m 1980;24:317-29. 12. SilnessJ. Periodontal conditions in patients treated with dental bridges. J Periodont Res 1970;5:60-8. 13. Silness J. Periodontal conditions in patients treated with dental bridges. Part II. J Periodont Res 1970;5:219-24. 14. SilnessJ. Periodontal conditions in patients treated with dental bridges. Part III. J Periodont Res 1970;5:225-9. 15. Renggli HH, Rengolati B. Gingival inflammation and plaque accumulation by well-adapted supragingival and subgingival proximal restoration. Helv Odontol Acta 1972;16:99-101. 16. Karlsen K. Gingival reactions to dental restorations. Acta Odontol Stand 1970;28:895-904. 17. Richter W , Ueno H. Relationship of crown margin placement to gingival inflammation. J PROSTHETDENT 1973;30:156-61. 18 Muller HP. The effect of artificial crown margins at the gingival margin on the periodontal conditions in a group of periodontally supervised patients treated with fixed bridges. J Clii Periodontol1986;13:97-102. 19. Bergman B, Hugson A, Olson CO. Periodontal and prosthetic conditions in patients treated with removable partial dentures and artificial crowns. Acta Odontol Stand 1971;29:621-38. 20. Valderhaug J, Birkeland JM. Periodontal conditions in patient five years following insertion of fixed prostheses. J Oral Rehabil1976;3:23743. 21. Newcomb G. The relationship between the location of subgingival crown margins and inflammation. J Periodontol 1974;45:151-4.
135
22. Fkm+bk&y
L, &@og+os
&rg$$ foo(it;loli @..ueand !&or Dent’ w-206. 23.
24. 25. 26. 27.
Gf2, Cimcio S. The effect of cmwn periodontal
health. Int J Pericdont
Re-
%#@a~,~~-~~l~~~
of niekle based dental alloys. CDAJ 1984; 1245-51. ZwderHA; E&et of silicate cement and amalgam on the gingiva. J Am Dent Asaoe~196~;65:11-5. Waerhaag J.-&$Xectofzinc phosphate cement fillings on gingival tissues. J P&&n&l l&%$7:284-91. Leon AR. The periodontium and restorative procedures. A critical review. J Oral R&tbil 1977;4:104-7. Waerhaugh J. Effect of rough surfaces upon gingival tissue. J Dent Res
1%6;35:823-5. 28. Sotres LS, Van Huysen G, Gilmore HW. A histologic study of gingival
$i&uerespCnse to amalgam, silicate, and resin restorations. J Periodonto1 1969;4&548-6. 29. Lang NP,Kiel -$U, Anderbalden K. Clinical and microbiological effects of ~~~~~~ions with overhanging or clinically perfect margips. J f.?l.&Pericdontol 1983;10:563-78. 30. St.& RE; Kuwata M. A dentist and a dental technologist analyze current cermo-metal procedures. Dent Clin North Am 1977;21:729-49. 31. Wheeler RC. Complete crown form and the periodontium. J PROSTHET DENT 1961;11:722-34.
32. W&gold AS. Tooth preparation in fixed prosthesis (Part I). Compend Co&n Educ Dent 1980;6:375-83. 33. Perel I&& k&l
c’own contours.
J PROSTHET DENT 1971;25:642-9.
34. P&iitin~CO. E&es&e crown contours facilitate endemic plaque nicl+s. J Pwnr DENT 197%35:424-g. 35. Yimdelk RA, Weaver JD, Sapkos S. Facial and lingual contours of artificial compl& crown restorations and their effects on the periodontium. J PROSTFSET DENT 1972;29:61-6. 36. Ghriste&sen GJ. Marginal fit of gold inlay castings. J PROSTHET DENT i9tqm297m5. 37. Ke&he$i G, &abo I. Intluence of class II amalgam fillings on attachment loss. J Clin Periodontol 19&L;11:81-6. 38. I-%kkarainen K, Ainamo J. Influence of overhanging posterior tooth restorations on alveolar bone height in adults. J Clin Periodontol I980;7:114-20.
1 I
i I i
Bound
volumes
available
39. Jeffcoat MK, Howell TH. Alveolar bone destruction due to overhanging amalgam in periodontal disease. J Periodontal 1984)$X:599-602. 40. Ochsenbeen C, Ross S. A concept of osseous surgery and its clinical application. Chap 13 In: Ward HL, ed. A periodontal point of vieur Springfield, Ill; Charles C. Thomas, Publ, 1973. 41. Wennstrom J, Lindhe J. Role of attached gingiva for maintenance of periodontal health. J Clin Periodontol 1983;10:206-21. 42. Dorfman HS, Kennedy JE, Bird WC. Longitudinal evaluation of free autogenous gingival grafts. J Clin Periodontol 1980;7:316-24. 43. Ericsson I, Lindhe J. Recession in sites with inadequate width of the keratinized gingiva. An experimental study in the dog. J Clin Periodonto1 1984;11:95-103. 44. Maynard JG, Wilson RD. Physiologic dimensions of the periodontium significant to the restorative dentist. J Periodontol 1979;50:170-4. 45. Ingber JS, Rose LF, Coslet JG. The “biologic width”-a concept in periodontics and restorative dentistry. Alpha Omegan 1977;70:62-5. 46. Gargiuilo AW, Wentz FM, Orban B. Dimensions and relations of the dentogingival junction in humans. J Periodontol 1961;32:261-7. 47. Tarnow D, Stab1 SS, Magner A, Zamzok J. Human gingival attachment responses to subgingival crown placement. Marginal remodelling. J Clin Periodontol 1986;13:563-9. 48. Listgarten MA. Periodontal probing: what does it mean? J Clin Periodonto1 1980;7:165-76. 49. Armitage GC, Svanberg GK, L6e H. Microscopic evaluation of clinical measurements of connective tissue attachment levels. J Clin Periodonto1 1977;4:173-90. 50. Saglie R, Johansen JR, Flotra L. The zone of completely and partially destructed periodontal fibers in pathologic pockets. J Clin Periodontol 1975;2:198-202. Reprint requests to: DR. WILLIAM G. REEVES COLLEGEOFDENTISTRY UNIVERSITY OF OKLAHOMA P.O.Box 26901 ~OO~STANTONL.YOUNG BLVD. OKLAHOMA CITY,OK 73190
to subscribers
Bound volumes of THE JOURNAL OF PROSTHETIC DENTISTRY are available to subscribers (only) for the 1991 issues from the publisher at a cost of $50.00 ($63.00 international) for Vol. 65 (January-June) and Vol. 66 (July-December). Shipping charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Volumes 63 and 64 are also available. Payment must accompany all orders. Contact Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, USA; phone (800) 325-4177, ext. 4351. Subscriptions must be in force to quakfy. Bound volumes are not available in place of a regular JOURNAL subscription.
DECEMBER
1991
VOLUME
66
NUMBER
6
