Translational and rotational accuracy of the mandibular proximal segment after virtual surgical planning-guided bilateral sagittal split ramus osteotomy in skeletal Class III patients.

Abstract

Previous studies on proximal segment accuracy after bilateral sagittal split ramus osteotomy have mainly focused on condylar position. This retrospective cohort study evaluated landmark-specific and direction-sensitive proximal segment discrepancies relative to the virtual surgical plan in 108 skeletal Class III patients who underwent virtual surgical planning-guided orthognathic surgery with bilateral sagittal split ramus osteotomy. Postoperative cone-beam computed tomography data obtained within 1 week after surgery were superimposed on the planned dataset. Five landmarks were evaluated on each proximal segment: condyle, coronoid process, anterior ramus, posterior ramus, and cutting edge. Translational discrepancies were assessed using signed X-, Y-, and Z-axis differences and three-dimensional (3D) discrepancies, and signed angular discrepancies in pitch, roll, and yaw were analyzed. Condylar landmarks showed relatively small 3D discrepancies, whereas larger discrepancies were observed at the posterior ramus and cutting edge landmarks, resulting in an overall 3D discrepancy of 1.94 ± 0.54 mm. Landmark-specific signed analysis demonstrated medial convergence of the coronoid processes, lateral deviation of the posterior ramus landmarks, and anterior deviation of the anterior ramus, posterior ramus, and cutting edge landmarks. These findings suggest that condylar accuracy alone may underestimate residual proximal segment discrepancy and support careful intraoperative assessment of passive proximal segment seating when proximal-distal segment interference is suspected.