Osseous surgery for crown lengthening: a 6-month clinical study.

BACKGROUND

Despite the fact that surgical crown lengthening is a commonly performed treatment, little is known about the specific surgical endpoints of the procedure or the stability of the newly attained crown height over time. Recent clinical reports have ranged across a spectrum from significant tissue rebound to remarkable stability using similar surgical techniques. The purpose of this study was to assess the stability of surgical crown lengthening procedures performed by various surgeons using specific guidelines to determine surgical endpoints. Specifically, we sought to determine the following: 1) What is the immediate increase in clinical crown height following surgery? 2) How stable is the established crown length over a 6-month period? 3) How much supporting bone is removed to establish the new crown length? 4) How does the position of the flap margin relative to the alveolar bone at surgical closure relate to the stability of crown height?

METHODS

Twenty-five patients requiring crown lengthening of 43 teeth were included in this study. Clinical indices recorded at eight sites on each molar and six sites on each premolar included plaque, bleeding on probing, probing depth, and relative attachment level from a customized probing stent. Surgical measurements at the same sites included the distance from stent to alveolar bone both before and after osseous surgery and the distance from flap margin to alveolar bone after suturing. Clinical measurements were repeated at 1, 3, and 6 months after surgery. Sites were divided into three groups. All sites on teeth targeted for crown lengthening were labeled treated sites (TT). Interproximal sites on neighboring teeth were labeled adjacent (AA) if they shared a proximal surface with a treated tooth and nonadjacent (AN) if they were on the opposite side, away from the treated tooth.

RESULTS

Throughout the entire 6-month healing period, descriptive statistics revealed no significant time or group differences in plaque and bleeding scores. At treated sites, the mean gain of crown height at surgery was 2.27 +/- 1.1 mm. This was reduced to 1.91 +/- 1.08 mm at 1 month, 1.69 +/- 1.02 mm at 3 months, and 1.57 +/- 1.01 mm at 6 months. At adjacent sites, the gain of crown length was 2.18 +/- 0.98 mm, 1.61 +/- 0.98 mm, 1.43 +/- 0.96 mm, and 1.30 +/- 0.96 mm at surgery, 1, 3, and 6 months, respectively. At non-adjacent sites the crown height increased 1.06 +/- 1.07 mm, 1.00 +/- 0.93 mm, 0.84 +/- 1.00 mm, and 0.76 +/- 0.85 mm, respectively. These mean measurements were significantly different for each treatment group at each time interval and appeared not to have stabilized between 3 and 6 months. The mean osseous reduction at treated, adjacent, and non-adjacent sites was 1.13 +/- 0.90 mm, 0. 78 +/- 0.75 mm, and 0.065 +/- 0.69 mm, respectively. Frequency distribution of osseous reduction demonstrated that 23.6% of treated sites had 0 mm, 44.3% had 1 mm, 25.4% had 2 mm, 6.2% had 3 mm, and less than I % had > or = 4 mm of bone removed to establish crown height More bone removal was noted at premolar than at molar sites; however, this was not statistically significant. When tissue rebound following surgery was plotted against post-surgical flap position, it was noted that the closer the flap margin was sutured to the alveolar crest, the greater the tissue rebound during the post-surgical period. This rebound ranged from 1.33 +/- 1.02 mm when the flap was sutured < or = 1 mm from the alveolar crest, to -0.16 +/- 1.15 mm when the flap was sutured > or = 4 mm from the alveolar crest.

CONCLUSIONS

These data suggest that there is a significant tissue rebound following crown-lengthening surgery that has not fully stabilized by 6 months. The amount of tissue rebound seems related to the position of the flap relative to the alveolar crest at suturing. These findings support the premise that clinicians should establish proper crown height during surgery without overreliance on flap placement at the osseous crest.