Three Parameters Impact the Perception of Smile Asymmetry in Patients with Facial Paralysis

Background: The ability to smile is impaired in patients with facial palsy, and objective parameters assessing smile symmetry to guide treatment are not well elucidated. Objective: This study seeks to identify objective facial measurements that relate smile recognition, perception of smile asymmetry, and perceived emotions from photographs of individuals with asymmetrical smiles compared with control photographs of individuals without smile asymmetry as measured by a photograph analysis application. Methods: Fifty-six photographs of smiles were categorized using objective perioral morphometric measurements (Emotrics). A photographic survey of these smiles was disseminated with queries regarding smile symmetry, smile recognition, and emotion perception. Generalized linear mixed modeling (GLMM) was performed to assess the effect of facial measurements on survey responses. Results: From 756 survey responses, smile symmetry predicted for smile recognition (F = 1084, p < 0.001) and emotion perception (F = 422, p < 0.001). Correlation analysis and GLMM identified three parameters (lower lip height, commissure position, and commissure height) that predicted smile recognition (F = 1040, p < 0.001), emotion perception (F = 976, p < 0.001), and symmetry (F = 1248, p < 0.001). Lower lip height (beta = -57.84, p < 0.001) and commissure position (beta = -29.41, p < 0.001) were the most significant drivers. Conclusions: Correcting lower lip height and commissure position represents efficacious clinical benchmarks for improving smile recognition by reducing smile asymmetry and conveying negative emotions.