Free gingival groove as a landmark for anatomical crown length in altered passive eruption

Identifying the cementoenamel junction (CEJ) in patients with altered passive eruption (APE) can be challenging during esthetic crown lengthening. The free gingival groove (FGG) may serve as a useful landmark for estimating CEJ position. This study evaluated the agreement between FGG and surgically identified CEJ, and explored additional photographic variables for CEJ prediction when FGG was not clearly identifiable.

This retrospective study analyzed presurgical and flap-reflected intraoral photographs of teeth 13-23 from 48 patients with APE who underwent esthetic crown lengthening at a university periodontal clinic. Proportion-based measurements were obtained in ImageJ by a calibrated examiner. The percentage of crown width to the distance from the incisal edge to the FGG (%WIFR) was measured on presurgical photographs, and the percentage of crown width to anatomical crown length (%WALR) was measured on flap-reflected photographs as the reference for CEJ position.

%WIFR showed strong agreement with %WALR across all teeth (R ² = 0.941, P < 0.001). The association was weakest in lateral incisors compared with central incisors and canines. Type I subgroup B showed evidence of effect modification of the %WIFR-%WALR relationship. When FGG was not clearly identifiable, a stepwise regression model incorporating other photographic variables provided a prediction of %WALR (R ² = 0.824, P < 0.001).

Standardized intraoral photographs can support clinically applicable CEJ estimation in APE, using the FGG as the primary landmark and a proportion-based prediction model as an alternative approach.