Three-dimensional perception of facial asymmetry.

In orthodontic diagnosis, facial symmetry is important. The aim of the present study was to analyse the perception of various degrees of facial asymmetry exhibited by carefully designed virtual three-dimensional (3D) material. Three groups of raters (30 orthodontists, 30 maxillofacial surgeons, and 30 laymen) rated, using a six-point scale, the degree of asymmetry of eight randomly presented 3D faces exhibiting incremental soft tissue alterations. The faces were created by gradually transforming the nose or chin in increments of 2 mm away from the computed symmetry plane. Differences between the groups in analysis of facial asymmetry, the rating of facial stimulus, and right and left facial asymmetry were determined using a t-test. The results demonstrated that raters' profession did not influence the point at which they identified asymmetry. Even laymen were able to detect asymmetries when located near the midline of 3D faces. All raters identified asymmetries of the nose as more negative than those of the same degree of the chin. A left-sided deviation of the nose along the facial symmetry plane lead to a more negative rating of facial appearance, whereas a right-sided deviation of the chin was rated as less attractive. Nasal architecture plays a crucial role in the perception of symmetry. These findings provide clinicians with a greater understanding of how faces are perceived, a process which is of particular interest in treating orthognathic patients, and those with congenital anomalies.