Facial symmetry is a key determinant of aesthetics, and facial asymmetry can significantly affect self-confidence and social interactions (Botezatu et al., 2024). Among various types of facial asymmetry, lower facial asymmetry is the most prevalent and often stems from skeletal discrepancies, particularly in skeletal class III malocclusion (Severt and Proffit, 1997). Chew et al. reported that 48 % of skeletal class III patients present with asymmetric mandibular prognathism, contributing to lower facial asymmetry (Chew, 2006). To correct mandibular protrusion and restore facial symmetry, orthognathic procedures such as bilateral sagittal split ramus osteotomy (BSSRO) are commonly employed (Li et al., 2017). Immediately after surgery, facial symmetry improves as the deviated distal segment is repositioned along the facial midline (Liu and Li, 2022). However, two critical questions remain unanswered: (1) To what extent does BSRRO enhances mandibular symmetry? (2) Do the surgically unaltered, asymmetric proximal segments undergo postoperative remodeling?

We hypothesize that mandibular symmetry improvement after BSSRO occurs in two distinct stages: Stage 1 (surgical correction), initial symmetry enhancement is achieved by repositioning the deviated distal segment, reducing positional discrepancies. Stage 2 (spontaneous remodeling), further symmetry refinement occurs through postoperative bony remodeling of mandibular body and ramus, correcting their pre-existing morphological asymmetry. To test these hypotheses, we analyzed positional and volumetric parameters of mandible at three time points: T0 (preoperative), T1 (immediate postoperative), T2 (≥6 months postoperative). By tracking these changes, we aim to elucidate the dynamic process of the mandibular symmetry transformation following BSSRO.