The effect of smiling on facial asymmetry in adults: a 3D evaluation
Published Online: Aug 15, 2021
Page range: 132 - 137
Received: Jan 01, 2015
Accepted: Sep 01, 2015
DOI: https://doi.org/10.21307/aoj-2020-147
Keywords
© 2015 Laura J. Darby et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.
Background/aims
Mild resting facial asymmetry exists in clinically symmetrical faces, but the effect of smiling on the magnitude of overall facial asymmetry in adults has not been assessed. The aim of the present study was to use stereophotogrammetry to quantify the effect of smiling on overall facial asymmetry in Caucasian adults who presented with Class I incisor relationships and no history of orthodontic treatment.
Methods
Twenty male and 20 female Caucasians aged 18–30 years with no history of orthodontic treatment, a clinically symmetrical face and a Class I incisor relationship had 3D stereophotogrammetric images captured at rest and on natural and maximal smile (T1). The images were repeated 2–4 weeks later (T2) to assess expression reproducibility. Overall facial asymmetry scores were produced from 27 landmarks using partial Ordinary Procrustes Analysis (OPA) and assessed by an Analysis of Covariance (ANCOVA) model. A random sample of the images was re-examined two months later to calculate intraobserver landmark reproducibility.
Results
Mean landmark error was low (0.41 ± 0.07 mm). Mean overall facial asymmetry scores were not significantly gender different (
Conclusions/implications
Overall 3D facial asymmetry scores for the sampled Caucasian adults with clinically symmetrical faces increased in magnitude from rest to natural and to maximal smile. Clinicians should assess overall facial asymmetry at rest and on natural and maximal smile at baseline, during treatment and as part of a core outcome assessment, particularly for cases with unilateral posterior crossbite, unilateral cleft lip and palate or skeletal asymmetry.