Purpose: To illustrate the use of a method that has been developed to assess the facial bone symmetry in 3D using no landmark.

Patients and methods: The program is based on the optimal symmetry planes (OSPs), which are the median planes fitted to show the highest ratio of voxel pairing on the 2 sides of the computerized tomography images of the facial skeleton. The deviation angles (angles between the OSP of the midface and the mandible) and the deviation distances (distances between the 2 planes at the lower borders of the mandibles) were determined. Methods are illustrated with 9 normal subjects and 31 subjects with facial asymmetries and differences in measurements between the two groups of subjects were tested for statistical significance.

Results: Measurements based on the OSP were significantly different between the two groups of subjects ( p < 0.001). Low ratio of voxel pairing of the midface or mandible was associated with greater deflection of the OSP of the mandible ( p < 0.05).

Conclusions: Measurements based on the method were different in subjects with and without facial–skeletal asymmetries. This method has several special features: (1) automatic computing for planes of midface and mandible; (2) assesses all hard tissue using no landmark; (3) quantitative assessment in an understandable way; (4) results illustrated in 3D figures. The quantitative results and the illustrations obtained by the program can be useful in the diagnosis and management of the asymmetrical facial skeleton.