Morphological differences in lower facial third soft tissues in children with and without gingival smile: A cross-sectional comparative study.

Aim: The aim of the present study was to establish the relationship between lower facial third and smile type in silent mixed-dentition patients.

Methods: This cross-sectional study, approved by the ethics committee, was conducted in a population of 2760 children, from which a convenient sample of 198 was included: 75 with gingival smile (GS) and 123 without GS (1:1.64). Clinical examination and videos were taken. Occlusal relation, overjet (OJ), overbite (OB), superior lip length at rest, superior lip length while smiling (SLLS), lower facial third height (LFTH), mid-facial third height (MFTH), clinical crown length, and lip lift ability (LLA) were measured by two calibrated examiners (intraclass correlation coefficient: ≥.95). A normality test and demographic and bivariate analyses were undertaken. A non-paired Student's t test was carried out in order to observe statistically-significant differences between variables.

Results: There were no differences between sexes or associations between LFTH and GS. Statistically-significant differences (P < .05) in MFTH, SLLS, LLA, OJ, and OB were found. A logistic regression model showed that the sum of LLA (odds ratio [OR]: .65, 95% confidence intervals [CI]: .50,.83]) and OB (OR: .88, 95% CI: .82, .93]) were GS predictive factors in 81.3% of cases.

Conclusions: OB and LLA are GS predictive factors in prepubertal participants. There is no relation between LFTH and GS.