Evaluation of therapeutic effect of virtual design for correcting facial asymmetry of skeletal Class Ⅲ deformity

Abstract

Objective: To establish a computer-aided surgical simulation procedure based on the natural head position(NHP) for orthognathic surgery and to access the effect for correcting facial asymmetry for skeletal Class Ⅲ deformity. Methods: Thirty-five patients(male: 14 and female: 21, mean age: [21.5±2.3] years) of skeletal Class Ⅲ deformity with facial asymmetry were included and divided into virtual group (16 patients) and control group(19 patients). The computer-aided surgical simulation procedure was used in the virtual group and the intermediate and final splints were fabricated using the rapid protyping technique. The traditional model surgery based on plaster casts was used in control group, and the splints were handmade. To evaluate the symmetry, three-dimensional(3D) photos were taken for all the patients before operation and 6 months after operation using the 3dMD face imaging system. Coordinate system was built based on mirror-original alignment method on the 3D photo. Thirteen soft tissue landmarks were marked on each 3D photo. The asymmetry index(AI) of those soft tissue landmarks was calculated. Results: There was no significant difference in the AI values between the two groups before surgery. Sixth month after operation, the mean AI values in the virtual group were (0.81±0.50) mm for subnasale, (1.01±0.80) mm for labiale superius, (1.94±1.30) mm for crista philtri, (1.60±1.20) mm for pogonion and (5.68±2.25) mm for gonion. The mean AI values in the control group were (1.49±1.10) mm for subnasale, (1.79±1.33) mm for labiale superius, (3.52±2.50) mm for crista philtri, (2.79±2.08) mm for pogonion and (8.43±3.94) mm for gonion and those indexes were significantly different between the two groups(P<0.05). There was no significant difference in the AI values of the pronasale, alare, labiale inferius and cheilion between the two groups sixth month after operation. Conclusions: The introduced procedure of the virtual design based on the estimated NHP could more effectively correct the asymmetry deformity for the skeletal Class Ⅲ patients.