Modification of Sagittal Split Osteotomy in Class II Asymmetry: Optimizing Bone Contact between Proximal and Distal Segments

Background: Computer-assisted surgical simulation (CASS) allows more precise orthognathic surgery. However, few studies have evaluated associations between CASS-designed bilateral sagittal split osteotomy (SSO) and bone contact surface in class II mandibular asymmetry. This study aims to evaluate the effects of using computer-assisted simulation and design modification of SSO to improve bony contact in skeletal class II asymmetry. Methods: This retrospective analysis reviewed 28 patients with class II asymmetry who underwent orthognathic surgery, including 15 with modified SSO (group CS) and 13 with conventional SSO (group C). Modified SSO was designed under CASS. Operative characteristics, postoperative outcomes, and complications were collected and compared between the two groups. Results: Bony contact was found at the distal end of the proximal segment in all group CS patients, while bone gap was noted in all group C patients (P < 0.05). Moreover, bone graft was used in four group C patients but was not used in all cases in group CS patients (P < 0.05). A trend toward lower operative time or perioperative bleeding was noted in group CS, but without statistical significance. After 1-year follow-up, inferior alveolar nerve disturbances were noted in two group CS patients and one group C patient. Palpable bone gap with uneven jaw line was noted in two group C patients 1 year after surgery and one patient received fat graft treatment. Conclusion: The simulation-based SSO modification provides appropriate contact surface and eliminates the bone gap between proximal and distal segments in class II asymmetry.