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When a Smile No Longer Conveys Happiness: Perception of Asymmetry by the General Public
Rachel Skladman, MD1; Gary Skolnick, MBA2; Snyder-Warwick K Alison, MD3
1Washington University in St. Louis School of Medicine, St. Louis, MO; 2Washington University School of Medicine, Saint Louis, MO; 3Department of Surgery, Division of Plastic and Reconstructive Surgery, Washington University School of Medicine, Saint Louis, MO

Introduction: Facial palsy exceeds 150,000 cases per year in the U.S.. Patients with facial palsy bear an enormous psychosocial burden as facial expressions are integral to nonverbal communication. Dynamic smile reconstruction is a goal of care, with the aim of creating symmetry. Defining appropriate outcome measures is challenging, however. Statistically significant smile measurements may or may not impart clinical significance. The purpose of this project is to evaluate how much asymmetry is tolerated in smile perception and to quantify that asymmetry.
Methods: Fifty-six facial photographs were assigned into three categories based on decreasing smile symmetry. Emotrics software was used to compute 12 bilateral facial measurements. Absolute and percentage deviation were calculated for five metrics most pertinent to smile symmetry. A Qualtrics survey consisting of 56 cropped photographs showing only the mouth was created and disseminated using Amazon’s Mechanical Turk (MTurk). Each photograph was accompanied by three questions: 1) Is the person smiling? 2) What emotion is being expressed? 3) How symmetric is the facial expression from 0-100? ANOVA, chi-squared, and multivariable linear modeling were performed using SPSS.
Results: Analysis included 610 survey responses. Recognizing smile in the depicted facial expression depended on symmetry. 100%, 78%, and 33% of completely symmetric, mild-moderate, and asymmetric smiles were recognized as “smiles,” respectively (p<0.001). The emotion identified in 89% of symmetric smiles was “happy”, compared to 15% of asymmetric smiles (p<0.001). Asymmetric smiles were perceived to convey “disgust” in 26% of photos (p<0.001). If the observer initially recognized a smile, there was a 65% likelihood the emotion identified was “happy”; conversely, if the smile was not recognized initially, it was most commonly identified as disgust (p<0.001). Statistically significant, multivariable linear models using asymmetry in five mouth measurements predicted: symmetry score, smile recognition, and whether the “happy” emotion was identified (p<0.001). A 1% increase in asymmetry of lower lip height and commissure position were associated with a decrease in symmetry score of 32 and 18 points, respectively.
Conclusions: Survey respondents from the general public were unable to recognize severely asymmetric smiles as “smiles.” Severely asymmetric smiles did not produce an expression perceived as a positive emotion, but instead conveyed a strongly negative emotion—disgust. Increases in asymmetry of lip or commissure position contribute to smile asymmetry and perceived negative emotion. These results may help interpret surgical outcomes and lead to informed consent discussions with patients.


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