Skeletal stability and occlusal plane changes in Class III orthognathic surgery: Comparison of clockwise and...

Occlusal plane (OP) rotation is frequently required during bimaxillary correction of skeletal Class III deformity, but its independent contribution to stability remains uncertain.

This prospective cohort study included adults with skeletal Class III deformity who completed presurgical orthodontic treatment and underwent bimaxillary orthognathic surgery. Patients were classified according to the change in OP angle from preoperative imaging (T0) to imaging obtained 1-2 days postoperatively (T1) as having an increased OP angle (clockwise rotation) or a decreased OP angle (counterclockwise rotation). Cone-beam computed tomography (CBCT) was performed at T0, T1, and 24 months postoperatively (T2). CBCT-derived lateral cephalometric measurements were used to quantify OP relapse and sagittal and vertical relapse at points A and B.

Eighty patients were analyzed (increased OP angle, n = 40; decreased OP angle, n = 40). Mean surgical OP change was 3.85 ± 0.89° in the increased-OP group and -3.60 ± 0.67° in the decreased-OP group. OP relapse was greater after decreased than increased OP rotation (1.10 ± 0.44° vs 0.77 ± 0.57°; P = .006). Sagittal relapse at point B was also greater in the decreased-OP group (0.70 ± 0.56 mm vs 0.30 ± 0.46 mm; P = .001), whereas maxillary relapse did not differ significantly. In the multivariable analyses, OP change was associated primarily with OP relapse, whereas linear skeletal relapse was associated mainly with the magnitude and direction of the initial jaw displacement. Most mean linear relapse values were approximately 1 mm or less, and all were below 2 mm.

OP direction was associated with rotational relapse but was not a stand-alone determinant of linear skeletal relapse. Although some between-group differences were statistically significant, their absolute magnitude was small and of limited clinical importance. OP rotation should therefore be incorporated into three-dimensional planning without being overinterpreted as a predictor of clinically important instability.