A 3D evaluation of facial asymmetry in mandibular prognathism subjects

Objectives: To evaluate the facial asymmetry in patients with mandibular prognathism using a three-dimensional method. Methods: The sample consisted of 32 subjects with previously taken CT scans, and mandibular prognathism (ANB<0°). The control group consisted of 11 subjects (7 females) with average age of 22.2 years ±2.3 and menton deviation of 2 degrees or less. The asymmetric group consisted of 21 subjects (8 females) averaging 22.3 years ±3.5, and menton deviation of 4 degrees or more. The x, y, and z coordinates of 23 landmarks (7 midline, and 8 bilateral) were collected for each subject. The bilateral landmarks' coordinates were compared to the contralateral side (deviated side minus contralateral) creating a dx, dy, dz set of coordinates for each group. These differences were compared between groups using the Hotelling's t2 test. Independent t-tests were used for the inter-group midline landmarks comparison, while paired t-tests were used for the intra-group deviated side versus contralateral comparison. Results: The control group had a mean ANB of -3.6±2.4 and mental deviation of 1±0.7, while the asymmetric group had -3.5±3 and 7.6±2.9, respectively. For the inter-group comparison, the midfacial landmarks of the lower jaw (Lower Incisor, B Point, Pogonion, Menton) and the bilateral landmarks of Gonion and Gonion Posterior showed significant difference (p<0.05). In the asymmetric group, Gonion, Gonion Lateralis, Gonion Posterior and Gonion Inferior showed significant difference between the deviated and the contralateral side (p<0.05). The symmetric group showed no significant difference between deviated and contralateral sides. Conclusions: Data suggests that when comparing symmetric and asymmetric mandibular prognathic subjects, only some landmarks in the mandible show a significant difference. The intra-group comparison showed a difference only in the asymmetric group.