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Understanding the Biologic Width

A Practical Approach

The term biologic width is familiar to most clinicians, yet there still exists confusion regarding its meaning and relevance to clinical procedures.1 According to Takei et al, the term “biologic width is used to describe the junctional epithelium and connective tissue that attach to the root surface.”2 Spear and Cooney refer to biologic width as the space that the healthy gingival tissues occupy above the alveolar bone.3

Combining the two definitions indicates that the soft tissue between the alveolar crest and the gingival sulcus is the biologic width, and it is composed of connective tissue and epithelium (Figure). Several studies have investigated the dimensions of this structure, including early reports by Gottlieb,4 Sicher,5 and the well-known study by Gargiulo et al.6 The latter was conducted on human cadavers and led the authors to establish what is now considered to be the standard measurements of biologic width (ie, 1.07 mm of connective tissue and 0.97 mm of epithelium). The total of the two structures is approximately 2 mm, which is an average of the biologic width around human teeth.

More recently, Vacek et al conducted a study on the dentogingival junction on 171 tooth surfaces from 10 adult human cadaver mandibles.7 Although the average values obtained from this study were similar to the dimensions obtained by Gargiulo et al, the Vacek findings revealed that there are several variations in dimension between subjects. Additionally, even within the same person, the biologic width changes depending on the location of the tooth in the dental arch. In fact, the reported values demonstrated that some individuals had an average biologic width of 0.75 mm, whereas others had 4.3 mm. As per the Gargiulo et al study, tissue that has higher variations in dimensions is the epithelial attachment, whereas the connective tissue attachment had the least variability.

While the average values given by both studies are still the general guidelines to follow in clinical dentistry, the issue becomes how to correctly measure the biologic width for each patient and for each tooth, and how to apply the information for procedures that involve daily restorative dentistry and periodontal surgical procedures.

 

Clinical Measurement

To properly measure the height of the biologic width, the clinician must anesthetize the gingival margin of the patient and probe to reach the sound bone level. Of that measurement, approximately 1 mm represents the typical physiological height of healthy gingival sulcus. Of course, the measurements must be taken on healthy periodontal and gingival tissues.3

Why it is important to measure the biologic width? Surgical crown lengthening procedures and gingival recontouring for aesthetic purposes are procedures that clinicians perform in an effort to biologically place a dental restoration or to satisfy aesthetic requirements,8 often for the anterior maxilla. Failing to recognize, understand, and carefully manage biologic width—or to violate it—can result in treatment failure.9 More specifically, Sonick stated that “violation of the biologic width can result in recession or inflammation.”10 Thus, the dilemma for the clinician is where to place the gingival margin for proper long-term clinical success, which includes not only function, but also aesthetics.

For ease of understanding and for practical reasons, the balance of this editorial uses 3 mm as the average measurement of the biologic width—inclusive of the sulcular epithelium. This dimension has been recommended for surgical crown lengthening procedures.11 When the clinician is treating teeth with subgingival caries, tooth fracture, inadequate clinical crown length, or aesthetic requests, it is recommended that the margins of the restorations be placed slightly below the gingival margin. In such cases, removal of soft tissue and bone is recommended in order to place the margins of the alveolar crest apically and to establish a distance of 3 mm between the bone level and the free gingival margin. The study by Landing et al examined the dimensions of the biologic width prior to as well as three and six months after surgical crown lengthening.11 The initial values of biologic width were re-gained six months following the surgical procedures. Of clinical relevance is the fact that the prosthetic treatment resumed six weeks after the surgical procedure.

(Continued from page 1 )

Respecting the Biologic Width

When placing the margin of a restoration in the gingival area of the tooth, it is crucial not to impinge on the biologic width. de Waal and Castellucci state that “the margin of the final prosthesis should be placed 1 mm to 2 mm supragingivally, wherever possible. If required for aesthetic considerations, the margin can be placed at the gingival crest or at most, 0.25 mm to 0.5 mm into the gingival sulcus. This ensures that the biologic width remains healthy.”12

In case of violation of the biologic width, Maynard and Wilson described inflammation that would progress apically, down-growth of the epithelial attachment, and, ultimately, loss of connective tissue attachment.13In the author's experience8, violation of the biologic width provokes an inflammatory response that results in alveolar bone resorption. This resorption provides space for a new connective tissue attachment, which results in greater sulcus depth or a true pocket. Additionally, often noted as consequences of apical migration of the attachment apparatus are increased pocket depths and the accumulation of subgingival plaque, leading to chronic inflammation and localized periodontal breakdown in susceptible patients.14

The fact that the body responds by recreating biologic width, which is a physiological process, means that even by performing marginal soft tissue recontouring for aesthetic reasons, the body itself will recreate the violated structure. In aesthetic dentistry, this last situation occurs when the clinician eliminates marginal tissue to create an even smile line. As a consequence, the marginal inflammation will cause some discomfort to the patient, as anecdotally reported.

It is of crucial importance to recognize the role of the gingival biotype. According to Muller and Eger,15 there are two biotypes: the first one is thin and the second one is thick. It is also important to recognize the biotype--type one will be more susceptible and weak to procedures, while type two will be more able to bear the traumatic insult.

A study conducted on 66 anterior subgingivally placed crowns in humans clearly demonstrated that the closer the margins of the crowns were to the biologic width, the greater was the likelihood or recording gingival inflammation.16 An experimental study was conducted on an animal model, in which the restorative margins were placed at different distances from the bone level.17 When the margins were at the bone level, 5 mm of bone loss were recorded; minimal or no resorption was noted when the margins were placed 4 mm above the bone level. It is important to note that bone resorption was more prominent in thinner cortical bone. In another animal study, Class V amalgam restorations were placed at the alveolar bone level after surgical exposure of the mandible.18 Biopsies were taken after approximately one year, revealing an average gingival recession of 3.15 mm and over 1 mm of bone loss; in control sites, the average recession was approximately 0.5 mm with only 0.15 mm of bone loss.

 Overall, it is important to approach the concept of biological width by examining its three-dimensional structure. This structure is composed of supracrestal fibers, connective tissue, junctional epithelium, attached gingiva, or, as defined by Schroeder and Listgarten, "the entire supra-alveolar fiber apparatus."19 The role of this entire apparatus is to protect the underlining alveolar bone and the periodontal ligament. It represents a seal between the body and the external world, and the dentist should try to keep this seal intact and healthy.

 

Conclusion

In conclusion, whether the clinician is performing surgical crown lengthening or soft tissue recontouring, the anatomical/histological presence of the biologic width has to be carefully evaluated and, regardless of the restorative and periodontal procedures, respected. Dental professionals must bear in mind that the recommended average dimension of the biologic width (ie, 3 mm) may not apply to all patients and all teeth. The clinician must carefully evaluate the biologic width of the adjacent teeth to properly complete the treatment, ensuring functional and aesthetic success.

 

*Professor, Department of Periodontics, Loma Linda University, School of Dentistry, Loma Linda, CA; Clinical Assistant Professor, Departments of Periodontics and Endodontics, State University of New York at Buffalo, School of Dental Medicine, Buffalo, NY; Manager, Applied Testing Center, Ivoclar Vivadent Inc, Amherst, NY.

 

References

 

  1. Padbury A Jr, Eber R, Wang HL. Interactions between the gingiva and the margin of restorations. J Clin Periodontol 2003;30(5):379-385.
  2. Takei HH, Azzi RA, Han TJ. Preparation of the periodontium for restorative dentistry. In Newman MG, Takei HH, Carranza FA, eds. Carranza’s Clinical Periodontology. 9th ed. Philadelphia, PA: W.B. Saunders; 2002:943-948.
  3. Spear FM, Cooney JP. Periodontal-restorative interrelationships. 949-964. In Newman MG, Takei HH, Carranza FA, eds. Carranza’s Clinical Periodontology. 9th ed. Philadelphia, PA: WB Saunders; 2002:943-948.
  4. Gottlieb B. Der Epithelansatz am Zahne. Deutsche Monatsschrift fur Zahnheilkunde 1921;5:142-144.
  5. Sicher H. Changing concepts of the supporting dental structures. Oral Surg Oral Med Oral Pathol 1959;12(1):31-35.
  6. Gargiulo AW, Wentz FM, Orban B. Dimensions and relations of the dentogingival junction humans. J Periodontol 1961:32:261-267.
  7. Vacek JS, Gher ME, Assad DA, et al. The dimensions of the human dentogingival junction. Int J Periodont Rest Dent 1994;14(2):154-165.
  8. Yeh S, Andreana S. Crown lengthening: Basic principles, indications, techniques and clinical case reports. NY State Dent J 2004;70(8):30-36.
  9. Schluger S, Youdelis R, Page RC, Johnson RH. Pre-prosthetic periodontal surgery. In Schluger S, Youdelis R, Page RC, Johnson RH, eds. Periodontal Diseases. 2nd ed. Philadelphia, PA: Lea & Febiger; 1990.
  10. Sonick M. Esthetic crown lengthening for maxillary anterior teeth. Compend Contin Educ Dent 1997;18(8):807-819.
  11. Lanning SK, Waldrop TC, Gunsolley JC, Maynard JG. Surgical crown lengthening: Evaluation of the biological width. J Periodontol 2003;74(4):468-474.
  12. de Waal H, Castellucci G. The importance of restorative margin placement to the biologic width and periodontal health. Part II. Int J Periodont Rest Dent 1994;14(1):70-83.
  13. Maynard JG Jr, Wilson RD. Physiologic dimensions of the periodontium significant to the restorative dentist. J Periodontol 1979;50(4):170-174.
  14. Allen EP. Mucogingival surgical procedures to enhance esthetics. Dent Clin North Am 1988;32(2):307-331.
  15. Muller HP, Eger T. Masticatory mucosa and periodontal phenotype: a review. Int J Periodont Rest Dent 2002;22(2):173-183.
  16. Newcomb GM. The relationship between the location of subgingival crown margins and gingival inflammation. J Periodontol 1974;45(3):151-154.
  17. Pama-Benfenati S, Fugazzotto PA, Ferreira PM, et al. The effect of restorative margins on the postsurgical development and nature of the periodontium. Part II. Anatomical considerations. Int J Periodont Rest Dent 1986;6(1):64-75.
  18. Tal H, Soldinger M, Dreiangel A, Pitaru S. Periodontal response to long-term abuse of the gingival attachment by supracrestal amalgam restorations. J Clin Periodontol 1989;16(10):654-659.
  19. Schroeder HE, Listgarten MA. The gingival tissues: The architecture of periodontal protection. Periodontol 2000 1997;13:91-120.

 

 

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