The determinants of successful distraction osteogenesis of the mandible in hemifacial microsomia from longitudinal results.

The purpose of this study was to investigate sagittal, vertical, asymmetric skeletal characteristics that could determine successful distraction osteogenesis (DO) of the mandible in patients with hemifacial microsomia using longitudinal follow-up data. Lateral and posteroanterior cephalometric radiographs before DO (T0), after DO (T1), and after retention (T2) were analyzed to investigate initial skeletal characteristics, DO effect, and retention. From the measurements at T2, patients were classified into group 1 (good retention results, N = 10) and group 2 (poor results, N = 9). Sagittal, vertical, dental, and asymmetric variables were measured. The differences at each stage and during T0-T1 and T1-T2 between two groups were compared by Mann-Whitney u test, Wilcoxon signed rank test and ANOVA test. Pruzansky type significantly influenced the success or failure of DO. At T0, group 2 showed more retrognathic mandible, smaller ramus height, larger gonial angle, more inward ramus inclination of the affected side, and more chin point deviation to the affected side than did group 1. The major effects of DO on group 1 were lengthening of the ramus height, forward positioning of the mandible, increase of gonial angle, counterclockwise rotation caused by a decrease of the articular angle, increase of ramus inclination of the affected side, and improvement of occlusal canting and chin point deviation. However, by DO, group 2 showed clockwise rotation of the mandible, and less increase of the ramus height than did group 1. After retention, group 2 showed counterclockwise rotation of the mandible and little growth of the ramus height. Group 1 showed reverse tendency. These factors could contribute to the difference in long-term results between two groups.