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Perception of facial asymmetry and a computational tool for its objective assessment Heda, Kiran


Background: Facial asymmetries have been reported with a prevalence range of 6% - 34% of the population. Unfortunately, there is no gold standard method for assessing facial asymmetry. Computational tools which utilize 3D-data to objectively quantify facial asymmetry, are needed. Purpose: Evaluate the reliability of examiners to assess facial asymmetry in set of 3D images of normal orthodontic population. Use an image-based computational tool - Dense Correspondence Analysis (DeCA), to objectively score facial asymmetry, and study its distribution in the different region of the face. Research Design: Facial surfaces were captured from CBCT records of 178 Orthodontic patients and 21 soft tissue landmarks were annotated. 12 subjects were selected which represented a range of facial asymmetry. 30 examiners belonging to 3 groups (laypersons, dental students, and orthodontists) were asked to rank the 12 subjects from most symmetric to asymmetric twice to calculate intra-rater and inter-rater reliability. The DeCA tool was used to calculate asymmetry scores in the overall facial surface and regional areas of the nose, upper lip, zygomatic region, and mandible. Descriptive statistics were performed to analyze distribution patterns of asymmetry. Results: Intra-examiner reliability was strong and Inter-examiner reliability was moderate for laypersons (0.36) and DMD students (0.44), but strong for the Orthodontist group (0.78). Quantification of asymmetry using DeCA indicated strong asymmetry in the zygomatic and mandibular regions, which were strongly correlated to each other (0.79), and to the overall facial asymmetry scores (r=0.92 and 0.93 respectively). No covariance between asymmetry scores and patients’ age or Angle’s Classification of malocclusion were noted. However, increased facial asymmetry was found in males compared to female subjects in the overall, zygomatic, and facial regions. There was weak-moderate concordance between the DeCA scores and averaged scores of the Orthodontist Group. Conclusion: Individual examiners are consistent at assessing facial asymmetry. There is poor agreement between examiners (except for the Orthodontist group) indicating a high degree of subjectivity in the assessment of this facial feature. The computational tool used here (DeCA) provides robust visualization of facial asymmetry in both the local and global regions of the face and allows for objective quantification.

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