Sex-related differences in skeletal relapse after bimaxillary orthognathic surgery: A retrospective case-control study.

Postoperative skeletal relapse remains a significant challenge following orthognathic surgery. While several risk factors, such as the magnitude of surgical movements and high preoperative mandibular plane angle, have been identified, the influence of biological sex on postoperative skeletal stability has not been well established. This study aimed to investigate sex-related differences in skeletal relapse after bimaxillary surgery with mandibular advancement. A matched retrospective case-control study was conducted in 70 patients (35 males, 35 females) who underwent bimaxillary orthognathic surgery at AZ Monica Antwerp (2018-2024). Patients were matched by age, mandibular advancement magnitude, and 1-year follow-up duration. Skeletal changes were assessed using 3D CBCT superimposition at three time points: preoperative (T0), immediate postoperative (T1), and 1-year follow-up (T2). (Clinically significant) mandibular relapse in all three directions at one year was low and did not differ significantly between males and females in any direction. The magnitude of intraoperative mandibular advancement was the strongest predictor of sagittal relapse (β = 0.28 mm per mm), and increasing patient age was associated with a modest reduction in relapse. Adding an interaction term between age and sex did not change the estimates. These findings confirm bimaxillary advancement surgery as a stable procedure regardless of sex.