Longitudinal observation of mandibular motion pattern in patients with skeletal Class III malocclusion subsequent to orthognathic surgery.

PURPOSE: The aims of the present study were to delineate the characteristic patterns of 3-dimensional (3D) mandibular movement in patients with skeletal Class III malocclusion compared with normal individuals and to investigate the longitudinal changes in mandible and condylar motion after orthognathic surgery (OGS).

PATIENTS AND METHODS: The subjects in the present prospective study consisted of 2 groups. The OGS group included 24 patients with skeletal Class III who underwent OGS. The control group consisted of 25 patients who underwent orthodontic treatment only. The patient records included demographic data, lateral and posteroanterior cephalometric radiographs before treatment, and serial mandibular motion data. In the OGS group, the mandibular motion data were obtained before OGS (T1), 1 month after OGS (T2), and at least 6 months after OGS (T3). The differences in cephalometric measurements and mandibular movements between the 2 groups were compared. The Pearson correlation test was performed to assess the relationship between the cephalometric measurements and the mandibular movements. Serial changes in mandibular movement in the OGS group were also compared.

RESULTS: The skeletal pattern in the OGS group demonstrated retrusive maxilla and a protrusive mandible, with a larger mandibular plane angle. For the incisal range of motion, the OGS group's maximal mouth opening was larger than the control group's by 6.9 mm. In the OGS group, the condylar range of motion in retrusion and the Bennett angle were asymmetric. Skeletal Class III patients tended to have a smaller range of condylar retrusion. At 1 month after OGS, the maximal incisal range of motion decreased from 57.23 to 25.61 mm. Other variables, including laterotrusion, movement velocity, and angle and distance of condylar movement in protrusion, reduced significantly. The Bennett angle demonstrated increased symmetry on both sides. Six months after OGS, the condylar motion in opening demonstrated improvements, but to a lesser extent than at T1. The condylar motion in retrusion recovered totally. The maximum incisal range of motion reduced slightly, but remained similar in value to that of the control group. The variables, including laterotrusion, movement velocity, and angle and distance of condylar movement in protrusion, demonstrated total recovery. The mandibular movement variables at T3 were not significantly different from those of the control group.

CONCLUSIONS: Skeletal Class III patients demonstrated a larger maximal mouth opening than did the controls, along with similar laterotrusion, but with a smaller retrusive condylar range of movement. The range of incisor motion and condylar movement did not correlate. The deterioration in mandibular motion after OGS can recover totally within 6 months. At T3, the mandibular movement remained consistent with the amount in normal subjects.