Abstract
Abstract 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 (p = 0.5300); therefore, the male and female data were pooled. Mean overall facial asymmetry scores for maximal (0.91 ± 0.16) and natural smile (0.88 ± 0.18) were higher than at rest (0.80 ± 0.17) (p < 0.0001) and were reproducible across (T1–T2) sessions (p = 0.3204). 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.
Highlights
Resting facial asymmetry exists in clinically symmetrical faces.[1]
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 with no history of orthodontic treatment
There were no statistically significant differences in mean overall facial asymmetry scores between sessions (p = 0.8547), facial asymmetry was reproducible for all expressions
Summary
Static facial asymmetry has been assessed using facial photographs, facial plaster casts and postero-anterior (PA) cephalograms. The reported studies have included children referred for orthodontic treatment[4] and Australian Orthodontic Journal Volume 31 No 2 November 2015 orthodontically-untreated adolescents and adults.[5,6] Facial asymmetry assessment has invariably used the mid-sagittal plane based on a variety of landmarks[3] or with 3D technology and geometric morphometrics.[5,6,7] Using stereophotogrammetry, a three-dimensional evaluation of facial asymmetry can be undertaken using statistical shape analysis of a combination of midline and bilateral landmarks.[7] This has been shown to be a valid and more robust approach compared with using a mid-sagittal facial plane.[8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
