Smile Reproducibility and Its Relationship to Self-Perceived Smile Attractiveness

SIMPLE SUMMARY: The smile plays an important role in personal, professional, and romantic relationships among humans. A smile may be posed or spontaneous, based on the external stimulus, and is characterised by a combination of facial movements that form the “smiling face”. Although the reproducibility of facial expressions, including the smile, has been studied before there are no reports on the reproducibility of the lip morphology upon smiling. Here, we assess a group of young adults who volunteered to pose for a social smile at two time points, four weeks apart. At the same visit they were also asked to assess the attractiveness of their own smile. Our results show that lip morphology during smiling is highly consistent among young adults. Females presented higher consistency in the shape of the smile, including lip morphology, compared to males. Self-perceived smile attractiveness was not associated to smile consistency. ABSTRACT: The reproducibility of facial expressions has been previously explored, however, there is no detailed information regarding the reproducibility of lip morphology forming a social smile. In this study, we recruited 93 young adults, aged 21–35 years old, who agreed to participate in two consecutive study visits four weeks apart. On each visit, they were asked to perform a social smile, which was captured on a 3D facial image acquired using the 3dMD camera system. Assessments of self-perceived smile attractiveness were also performed using a VAS scale. Lip morphology, including smile shape, was described using 62 landmarks and semi-landmarks. A Procrustes superimposition of each set of smiling configurations (first and second visit) was performed and the Euclidean distance between each landmark set was calculated. A linear regression model was used to test the association between smile consistency and self-perceived smile attractiveness. The results show that the average landmark distance between sessions did not exceed 1.5 mm, indicating high repeatability, and that females presented approximately 15% higher smile consistecy than males (p < 0.05). There was no statistically significant association between smile consistency and self-perceived smile attractiveness (η(2) = 0.015; p = 0.252), when controlling for the effect of sex and age.