Evaluation of Supracrestal Gingival Tissue After Surgical Crown Lengthening: A 6-Month Clinical Study

Background: Previous studies on crown lengthening (CL) report contradictory results regarding stability of crown length gained at the time of surgery. The "3-mm rule" has dictated the amount of alveolar bone to be removed during CL surgery for decades. With the current understanding of wide variations in supracrestal gingival tissue (SGT) dimensions, bone removal can be customized to the situation. The purpose of this study is to assess alterations in periodontal tissue levels 6 months after CL surgery and to evaluate factors that may influence stability of CL achieved over time. Methods: Sixty-four patients requiring CL surgery on 64 teeth are included in this study. Clinical parameters were recorded along six surfaces of treated tooth and neighboring teeth. Sites were labeled as treated sites, adjacent sites, and non-adjacent sites. Bone was reduced based on the minimal amount of tooth structure required for restorative purpose and SGT dimensions at each site. Patients were re-evaluated at 3 and 6 months. Results: Significant soft-tissue rebound (0.77 +/- 0.58 mm) was observed 6 months after CL surgery. This rebound was found to be significantly correlated with periodontal biotype (r = 0.325, P = 0.000) and post-suturing flap position (r = -0.601, P = 0.000). SGT was not reestablished to its preoperative dimensions by the end of 6 months (P = 0.001). Conclusions: Crown length gained during surgery significantly decreased 6 months post-surgery. Suturing the flap <= 3 mm from the osseous crest and thick-flat biotype were associated with greater tissue rebound.