An Evaluation of Facial Asymmetry Using Three-Dimensional Cone-Beam Computed Tomography

Aims: In the fields of orthodontics and dentofacial orthodpedics, oral and maxillofacial surgery, and craniofacial anomalies, a method to precisely identify, quantify, and diagnose facial asymmetries would be invaluable in the treatment and outcome of individuals with marked asymmetries. To date no studies have been published on asymmetry in living subjects using CBCT as an assessment tool. The aims of this study were to identify quantifiable differences between subjects with and without clinical asymmetry, to develop a practical, reproducible, user-friendly method of analyzing patients' symmetry in three dimensions using cone beam computed tomography and Dolphin 3D imaging software, and to quantify the amount of asymmetry in clinically symmetric patients. Materials and Methods: The cone beam computed tomography three dimensional scans of subjects presenting to the University of California San Francisco graduate orthodontic clinic were evaluated using traditional and novel points to study mandibular asymmetry. Thirty three individuals with no clinical asymmetry or midline deviation were selected as the control group and nineteen individuals with a chin point deviation were included in the asymmetry group. The scans were oriented in a novel, standardized method, then sixteen landmarks and twelve linear and angular measurements were studied. The average three dimensional difference between the right and left sides was calculated and graphically represented as an asymmetry index for the control group. Individual asymmetric subject's data was compared to this graphical norm to determine the specific location of asymmetry.Results: Error associated with the orientation method ranged from 0.83-2.09mm. In the control group, asymmetry ranged from 0.74mm for nasal height to 3.49mm for gonion. In the asymmetry group, asymmetry ranged from 0.71mm for ANS to 5.97mm for mandibular foramen. Conclusion: Substantial error, both in the orientation method and landmark identification, is associated with this method of three dimensional analysis. Statistical differences were found between mandibular points in two study groups. Although the analysis needs refinement, it can be used to identify the location of asymmetry in subjects with chin deviation and will be useful in the proper diagnosis, understanding, and treatment of individuals with these asymmetries