Comparative Analysis of Postoperative Relapse in Asymmetric and Symmetric Mandibles Following BSSRO for Class III Malocclusion.

Background: Bilateral sagittal split ramus osteotomy (BSSRO) is the gold-standard surgical treatment for mandibular prognathism and facial symmetry restoration in class III malocclusion. However, it remains unclear whether asymmetric and symmetric mandibles exhibit differential relapse patterns that impact both functional stability and aesthetic outcomes. This study aims to compare intraoperative displacement and postoperative skeletal relapse between asymmetric and symmetric mandibles following BSSRO.

Methods: This retrospective cohort study analyzed class III malocclusion patients who underwent BSSRO between January 2018 and December 2023. Three-dimensional CBCT datasets were obtained at three time points: preoperative (T0), immediately postoperative (T1), and at least 6 months postoperative (T2). Translational and rotational changes in mandibular segments (distal and proximal) were quantitatively assessed during surgical correction (T0-T1) and relapse (T1-T2).

Results: Intraoperatively, the asymmetric group (AG) exhibited greater displacement toward the non-deviated side of the distal segment (P=0.001) and movement of the non-deviated proximal segment toward the deviated side (P=0.044) compared to the symmetric group (SG). Rotational analysis revealed increased clockwise yaw in AG's distal segment (P=0.009) and enhanced clockwise roll in the non-deviated proximal segment (P=0.021). Postoperatively, AG demonstrated significant relapse toward the deviated side in both proximal segments (non-deviated side: P<0.001; deviated side: P=0.027), counterclockwise yaw in the distal segment (P=0.020), and a counterclockwise rolling tendency in the non-deviated proximal segment (P=0.050).

Conclusions: Asymmetric and symmetric mandibles exhibit distinct relapse patterns following BSSRO, involving both translational and rotational movements across all segments. These findings highlight the importance of individualized surgical planning and postoperative management in asymmetric cases. Further validation through prospective multicenter studies with long-term follow-up is recommended.

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