Rotation tendency of the posteriorly displaced proximal segment after vertical ramus osteotomy.

Intraoral Vertical Ramus Osteotomy (IVRO) is one of the operative techniques used for orthognathic surgery. The aim of this study was to assess the posterior displacement of the proximal segment in patients undergoing IVRO at 1-year follow-up. In total, 52 hemimandibles from 26 patients who underwent IVRO in whom the proximal segment was posteriorly displaced without overlap with the distal segment at immediate post-operation (Imm) (30 cases, experimental group), and 26 patients in whom the proximal segment was not posteriorly displaced with overlap with the distal segment (Imm) (22 cases, control group) under three-dimensional computed tomography (3D CT) were included in the study. To analyze the movement of segments, the positions of the mid condyle point (MCP) and angle of condyle line (Con) were determined and the movement of the ramus angle (posterior edge of proximal segments) was measured at the proximal segment. Regression of the proximal segment in sagittal direction of the MCP was observed in both groups and all directions of the ramus angle in the experimental group, and only sagittal direction in the control group. In conclusion, posterior displacement of the proximal segment after IVRO showed tendency to regress its original position.