Postsurgical Rotational Flare Between the Proximal and Distal Segments of the Mandible Following Mandibular Setback Surgery

OBJECTIVE: To investigate postsurgical rotational flare between the proximal and distal segments of the mandible following mandibular setback surgery using three-dimensional analysis. MATERIALS AND METHODS: Cone-beam computed tomography scans from 30 patients who underwent bilateral sagittal split ramus osteotomy were analysed. To minimise the influence of bone remodelling, the proximal segment (PS) at T1 (post-surgery) was superimposed onto the T2 (post-treatment) PS using stable reference areas, excluding the osteotomy sites, condyle, and gonial angle, to generate a modified T2 model. The T1 and modified T2 were then superimposed on the distal segment (DS), which served as the reference. Displacements of the medial and lateral condylar poles, coronion, and gonion were measured with respect to the DS. RESULTS: When assessed using the DS as reference, the medial pole, lateral pole, and coronion showed significant posterior displacements (1.21, 1.57, and 1.24 mm; p < 0.001). Coronion also moved superiorly (0.74 mm, p < 0.001) and laterally (0.43 mm, p = 0.004), while gonion moved medially (0.65 mm, p < 0.001) without significant anteroposterior change (p = 0.468). No significant correlation was found with setback amount, vertical bony step, or its resolution. CONCLUSION: The PS exhibited counterclockwise rotational flare and anterior-outward/posterior-inward yawing in relation to the DS. Incorporating surgical compensation for anticipated rotational flare-related relapse may enhance the predictability of mandibular setback outcomes.