Smile shape and self-perceived smile attractiveness

To assess the effect of smile shape on self-perceived smile attractiveness in young adults.

The study included 601 participants (393 females, 208 males). Three-dimensional smiling facial images were captured using the 3dMD stereophotogrammetry system (3dMD, Atlanta, USA). Participants rated their smile attractiveness using a visual analogue scale (0-100). Smile shape was described with 62 landmarks, which were aligned using Generalized Procrustes Superimposition to extract shape coordinates. Principal component analysis (PCA) was used to reduce dimensionality and derive shape PCs. The association between smile shape and self-perceived smile attractiveness was examined using multivariate regression models, performed separately for females and males. Allometric effects were assessed using standardized residuals of shape PCs. Statistical significance was set at P < .05.

In males, no statistically significant association was found between smile shape and self-perceived smile attractiveness (P = .6; η2 = 0.065). In females, a significant association was observed (P = .001; η2 = 0.093), with more attractive smiles displaying greater width, height, and curvature. Allometric analysis revealed a strong effect of size on shape (η2 = 0.468; P < .001). After controlling for this effect, the association in females was no longer statistically significant (P = .08), although a moderate effect size persisted (η2 = 0.069), indicating that the effect remained but was statistically less robust.

Smile shape significantly affects self-perceived attractiveness, particularly in females, with effects related to proportionally larger smiles. This finding highlights known sex-based differences in aesthetic self-perceptions, as well as the preference for broader smiles.