This observational study investigated the relationship between malocclusion and smiling.
Adolescents and young adults (n = 72; aged 16-25 years) were identified according to their Dental Aesthetic Index (DAI) and allocated to 3 groups: (1) malocclusion group (n = 24; DAI ≥31), (2) retention group (n = 24; pretreatment DAI ≥31) with a prior malocclusion that had been corrected by orthodontic treatment, (3) control group with no-to-minor malocclusion (n = 24; DAI ≤25). Participants were requested to watch an amusing video. Based on the Facial Action Coding System, automated pattern recognition was used to detect smile episodes and assess their frequency, duration, genuineness, intensity, and extent of tooth show. Demographics, Big Five personality dimensions, and self-perceived smile esthetics-related quality of life were collected from all participants via questionnaires. Data were analyzed by mixed-model analysis and adjusted for possible confounders.
Patients from the malocclusion and retention groups smiled significantly less than participants from the control group, with the duration of smiles and smiling time being around half those of control subjects. Smile genuineness, smile intensity, and teeth shown did not differ across groups. Personality traits did not differ significantly among the 3 groups, whereas the malocclusion group scored around 30% less for dental self-confidence than the other 2 groups.
Patients with severe malocclusion tend to smile less, but the features of their smiles are similar to those without malocclusion. A lower propensity to smile in patients with a corrected malocclusion may persist after orthodontic treatment.

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