DISTANCE FROM SYMMETRY - A 3-DIMENSIONAL EVALUATION OF FACIAL ASYMMETRY

Purpose: A new method for the quantification of facial asymmetry has b een developed and applied to a group of 80 young, healthy, white adult s with no craniofacial, dental, or mandibular disorders. The method ca lculates an asymmetry vector (distance from the symmetry) that allows both the quantification of the absolute degree of asymmetry and its th ree-dimensional direction and verse. Methods: For each subject, the th ree-dimensional coordinates of 16 standardized soft-tissue facial land marks (trichion, nasion, pronasale, subnasale, B point, pogonion, eye lateral canthi, nasal ala, labial commissure, tragus, gonion) were aut omatically collected using a noninvasive instrument. The coordinates u nderwent a four-step analysis: 1) calculation of the plane of symmetry , the facial centers of gravity, and the asymmetry vector in each subj ect; 2) calculation of the mean absolute asymmetry in each sample; 3) calculation of the mean asymmetry vector (resultant vector) in the pop ulation; and 4) calculation of the separate contributions of the singl e 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 fac e was larger than the left side.