Biologic Width – The New Magic Number is Here!
New research casts light, reveals surprising facts, and provides practical evidence-based recommendations.
Posted: September 22, 2015
When restorative dentistry enters the subgingival zone, respecting the biologic width (BW) is a key factor for maintaining periodontal health. Transient minor damage and inflammation often occurs during subgingival instrumentation procedures including tooth preparation and hygiene instrumentation. Fortunately this can usually resolve, especially in sites not afflicted by gingivitis; chronic periodontitis; and/or delicate, fragile or thin gingival tissue. However, major damage to the BW and/or permanently invading it with a restoration increases the risk for clinical attachment loss (increased probing depth and/or tissue recession).
Knowing the actual dimension of the BW would be very helpful, especially before placing restorations subgingivally where they may encroach on the BW. For several decades, authorities have recommended specific BW dimension numerical criteria for dentists to use in case planning and during clinical procedures. However, a recently published evidence-based systematic review sheds more light on this important clinical issue. Biologic width dimensions – a systematic review (Journal of Clinical Periodontology 2013; 40: 493-504) reveals startling news for those who want to rely on preset BW dimension numerical criteria: There are none. The authors determined that, “A magic number for the biologic width as a treatment objective cannot be recommended…” As stated in the conclusion, “No universal dimension of the biologic width appears to exist.”
In this study, BW was defined as, “the junctional epithelium and supracrestal connective tissue attachment surrounding every tooth”. Utilizing PRISMA (Preferred Reporting Items for Systematic Review and Meta-analyses) criteria, 615 papers (1924-2012) were evaluated, from which 14 were found to meet the systematic review criteria of which 6 were suitable for meta-analyses. Mean values of the BW dimension obtained from two meta-analyses ranged from 2.15 to 2.30mm but large intra- and inter-individual variances (0.2 -6.73mm) were observed. Furthermore, the authors noted substantial heterogeneity among studies existed with respect to methods and outcome measures.
Some of the underlying studies observed situations which potentially could alter the BW dimension. For example: BW dimension may decrease with increased probing depth; BW dimension may decrease with increased attachment loss; and BW dimension may increase from anterior to posterior. However, these observations have not yet been validated with sound research and as such, applying them to individual patients does not seem justified at present.
Nevertheless, this study provided six clinically useful tips:
- No universal dimension of the biologic width appears to exist. Although BW dimension mean values only ranged from 2.15 to 2.30mm, large intra- and inter-individual variances (0.2 -6.73mm) were observed. Accordingly, the investigators warned against using mean values for individual patients as they can mask the actual clinical situation.
- Before trying to estimate the BW dimension by periodontal and transgingival probing, the site should always be free of clinically detectable inflammation. Periodontal and transgingival probing are useful clinical methods to estimate BW dimension. However, periodontal probing accuracy is associated with the inflammatory state of the probed tissues. In the presence of inflammation the probe tip can penetrate the junctional epithelium portion of the BW and stop at the most coronal part of the non-inflamed connective tissue. Therefore, in the presence of inflammation, the BW appears to be less than it is at non-inflamed sites. An important conclusion of the study was that periodontal health should be established prior to assessing the BW dimension for restorative dentistry procedures.
- More accurate probing depth is achieved with gentle probing than with forceful probing. Gentle probing is approximately 25 gram force. Go to www.perioaccess.com and check out the Periodontal Examination Quick Reference Guide for quick and easy ways to do gentle, and more accurate probing.
- Transgingival probing depth is also influenced by probing force. This clinical method can be used to evaluate the alveolar bone level. Although it seems to be a reliable and accurate method for estimating bone level and osseous defects, the penetration depth is also affected by the amount of probing force: the more force used, the greater the penetration depth.
- To determine BW dimension for anterior teeth, a combination method also seems to produce reliable results. Performing both clinical and radiographic evaluation can help (gutta-percha points inserted into the gingival sulcus followed by two radiographs). The clinician must judge the potential benefit of radiographs versus the potential radiation risk on an individual case basis.
- Wait at least 6 months after surgical crown lengthening before assessing the BW dimension. After surgical crown lengthening it takes up to at least 6 months for the BW dimension to reestablish.
However, when crown lengthening is needed for a tooth, the clinician needs to estimate the BW dimension. Although there are likely many approaches to do so, a practical clinical approach incorporating the evidence noted above is offered below:
- Apply/incorporate clinical tips #s 2-6 noted above.
- Use the best available surrogate tooth/tooth area in the patients mouth and determine its BW dimension. For example, if crown lengthening is needed on the buccal aspect of a mandibular 2nd premolar, consider using the BW dimension data from the following:
- The lingual aspect of the same tooth if its subgingival environment, supporting tissues, arch prominence, etc. are similar to those on the buccal aspect.
- The buccal aspect of the contralateral 2nd premolar and/or adjacent 1st pre-molar (if these sites have similar supporting tissue thickness, alignment, subgingival environment, etc.).
Always use clinical judgment and the best available data derived from the individual patient when estimating the BW dimension needed for her/his tooth in question.
- When the clinical case allows it, as an additional safety buffer consider adding 0.5mm to the estimated BW dimension.
- If possible, position the gingival margin of the restoration ≥ 1mm coronal to the estimated BW dimension.
- Consider waiting at least 6 months to estimate the BW dimension after crown lengthening surgery especially for cases with esthetically critical gingival display that present with thicker, more durable/protective gingival tissue.
- Consider waiting at least 9 months to estimate the BW dimension after crown lengthening surgery especially for cases with esthetically critical gingival display that present with thinner, more fragile/delicate gingival tissue.
Although “a magic number for the biologic width as a treatment objective cannot be recommended” the paperBiologic width dimensions – a systematic review (Journal of Clinical Periodontology 2013; 40: 493-504) provides six clinically useful tips about BW dimension estimation that the clinician can immediately incorporate into her/his practice. A practical clinical approach is offered for estimating the BW dimension in the clinical setting.
George K. Merijohn, DDS
San Francisco periodontist George K. Merijohn practiced 28 years and is associate professor in postdoctoral periodontics at UC San Francisco and U Washington. He is appointed special expert to the California Dental Board; serves as a consultant to dental schools, clinicians, and the legal profession; and is on the editorial board of the Journal of Evidence-Based Dental Practice. Dr. Merijohn leads seminars and workshops at major dental conferences and is published in peer-reviewed journals with articles on mucogingival clinical decision-making, risk assessment, and the evidence-based approach. More about George >