Kois31 has coined three categories of biologic width based on sulcus depth and total attachment width. Referring to the bone level, he called these normal crest, high crest, and low crest. Crest refers to the facial height of bone as detected by a periodontal probe sounding to the bone through the sulcus. A normal crest is defined as 3 mm from the free gingival margin to the bone crest on the facial aspect of the tooth and 3.0 to 4.5 mm at the interproximal areas. A lesser number indicates a high crest, suggesting that bone is closer to the CEJ than normal. A low crest is farther away from the free gingival margin, indicating a larger total width of the dentogingival complex and the possibility of resecting gingiva without encroaching on a normal biologic width. Later Kois32 described preparation guidelines related to respecting the biologic width. For the normal crest dentogingival complex, the finish line on the facial aspect should be placed 0.5 to 1.0 mm below the free gingival margin.
When bone is lost in an uncontrolled fashion, the periodontal damage may result in either increased pocket depth or gingival recession. Because satisfactory esthetics requires a healthy and adequately contoured gingival frame surrounding the restoration, the stability of bone and attachment levels is essential. Just as bone supports the soft tissue to create the attractive, scalloped appearance of healthy gingiva, lost bone will typically translate to negative esthetic gingival changes.
Biologic width management and correction
If the restoration margin infringes on the biologic width, the natural width can be reestablished only by creating adequate distance between the free gingival margin and the bone crest. Such an infringement may be prevented by keeping the finish line of the tooth preparation and subsequently the margin of the restoration more coronal during tooth preparation. However, when it is necessary to extend the finish line apically, one of two courses of treatment may be selected. The first and most common choice is crown lengthening osseous surgery—resecting bone to restore a proper biologic width and positioning tissue in a manner that will maintain health and viable esthetics. The alternative is to consider orthodontic extrusion of the tooth, thus moving the margin in a coronal direction. Bone tends to follow the tooth movement, resulting in no net change in the attachment width; to prevent bone from following, fiberotomy is used during orthodontics,33–35 or limited crown lengthening surgery can be performed once orthodontics is complete. The authors concur with Berglundh et al36 that fiberotomy may not yield the complete desired lengthening, because the tissue continues to follow the tooth movement but to a lesser degree than without fiberotomy. In such cases, extrusion should be followed by additional surgery to establish biologic width and balance the esthetics.
The gingival attachment repairs itself after injury. With a clean injury, as in surgery, if all the tissue components remain, the connective tissue will reattach, and the epithelium will re-form its hemidesmosomal junction coronal to that connective tissue attachment. In primate models, this repair takes over 6 weeks.37 In humans, repair and remodeling can go on for much longer, ranging from 6 to 12 months.38 Lanning et al39 found that a normal biologic width and gingival dimension was restored after 6 months of healing. This was referenced to the new, more apical bone crest. Ganji et al40 found that biologic width is reestablished by 3 months after either osseous resective surgery or gingivectomy, although the osseous procedure was more effective for stability of clinical crown lengthening. To avoid confusion, the term osseous resective crown lengthening should be used.41
Gingivectomy addresses only the soft tissue component of the dentogingival complex. Because it does not change the level of bone and thus cannot relocate the level of the biologic attachment, gingivectomy risks encroachment on the healthy biologic width. As mentioned above, the periodontal probe extends partially into the attachment, resulting in a perception that the sulcus is deeper than it is biologically.24 Gingivectomy should only be considered if the tissue depth from the proposed free gingival margin to the level of the attachment is at least 3.0 mm, allowing for biologic width without bone resection. Regardless of choice of instrumentation, a residual sulcus of at least 1.5 mm should remain after soft tissue resection, or an osseous resective crown lengthening surgery should be performed.
When the soft tissue is placed apically to expose more coronal tooth structure, the tissue may remain stable where apically positioned, or it may rebound coronally, covering some of the previously exposed tooth structure and increasing the subgingival location of the crown margin. This too can be explained by the concept of biologic width. Flaps placed at the bone crest may not have room apically for a normal width. They may proliferate coronally until a normal width has occurred, as evidenced from greater rebound when positioned at the crest.42 This coronal migration is also more prevalent in patients with a thicker tissue type.41 Six months would be prudent to allow stable healing after osseous resective crown lengthening surgery, recognizing that minor further changes may occur for up to 12 months.43 Prior to commencing or continuing with definitive restorative procedures, clinicians should wait at least 3 months for healing after minor gingivectomy procedures and 6 to 12 months after osseous resective crown lengthening surgery.
Impact of restorations on gingival attachment
Both the restorative process and the resulting restorations have an impact on the gingival tissues. Preparation, provisionalization procedures, retraction and impression procedures, and delivery (conventional luting and adhesive cementation) procedures all irritate the tissue. Epithelium is typically disrupted or even removed by the aforementioned routine procedures. Emphasis should be placed on trying to accomplish the treatment with minimal irritation to the tissue and then allowing repair to begin (Fig 1-3). Cumulative irritation from repeated attempts to perform such procedures may result in longer duration of inflammation and greater remodeling of the attachment level.
Fig 1-3 (a and b) Facial views of teeth prepared for zirconia-based ceramic crowns with minimal trauma to the soft tissue. (c and d) Facial views of the zirconia-based ceramic crowns 1 year after delivery, demonstrating that the trauma to the soft tissue has been reversible. (e) Facial view of the crowns 4 years after delivery, demonstrating soft tissue stability around the crowns. (Ceramics: Andreas Saltzer.)
Marginal adaptation, cement line exposure, and restorative contours all influence future tissue health. Any contours or gaps that foster plaque accumulation increase the likelihood of inflammation. Inadequate preparation design in terms of axial reduction and finish line width may result in an overcontoured restoration. This is especially true at the facial aspect, where adequate thickness of restorative materials is necessary to provide adequate translucency and esthetics (Fig 1-4). Such overcontoured restorations may mechanically encourage tissue change, such as recession, as well as trap plaque. In animal model studies, overcontouring was found to increase plaque retention and contributed to higher loss of clinical attachment levels compared with normally contoured controls. Crowns that are comparably contoured to the original tooth form provided the highest levels of periodontal health. Despite greater attachment loss in overcontoured groups, carefully instituted hygiene procedures mitigated the damage to only slightly worse conditions than the controls.44
Fig 1-4 Facial view of failing metal-ceramic crowns. Note