Distance from symmetry: a three-dimensional evaluation of facial asymmetry

Abstract

Purpose: A new method for the quantification of facial asymmetry has been developed and applied to a group of 80 young, healthy, white adults with no craniofacial, dental, or mandibular disorders. The method calculates an asymmetry vector (distance from the symmetry) that allows both the quantification of the absolute degree of asymmetry and its three-dimensional direction and verse.

Methods: For each subject, the three-dimensional coordinates of 16 standardized soft-tissue facial landmarks (trichion, nasion, pronasale, subnasale, B point, pogonion, eye lateral canthi, nasal ala, labial commissure, tragus, gonion) were automatically collected using a noninvasive instrument. The coordinates underwent a four-step analysis: 1) calculation of the plane of symmetry, the facial centers of gravity, and the asymmetry vector in each subject; 2) calculation of the mean absolute asymmetry in each sample; 3) calculation of the mean asymmetry vector (resultant vector) in the population; and 4) calculation of the separate contributions of the single facial structures to the facial asymmetry.

Results: A certain degree of soft-tissue facial asymmetry was found both in the individuals and in the global population, and it was evident especially in the middle (tragus) and lower (gonion) thirds of the face. The right side of face was larger than the left side.