Three-dimensional analysis of condylar displacement and mandibular segment positions following bilateral sagittal split osteotomy advancement surgery planned with virtual surgical planning: a prospective cohort study

The bilateral sagittal split osteotomy (BSSO) is commonly used for mandibular advancement. This study assessed the three-dimensional accuracy of the virtual surgical planning (VSP) in predicting postoperative mandibular segment positions. Furthermore, the impact of surgical manoeuvres on these positions and their correlation with cephalometric measures were explored. Twenty patients undergoing BSSO advancement (in single- or two-jaw procedures) were treated based on VSP by an experienced surgeon using inter-occlusal wafers. Rigid-wise voxel-based registration was used to superimpose pre-surgical (T0) and post-surgical (T1) cone beam computed tomography images in three distinct regions. Results showed that VSP underestimated the posterior movement of the proximal segment by 0.98 mm (95% CI 1.63 mm to 0.33 mm) and its anterior pitch by 1.08° (95% CI 0.37-1.78°). Greater distal segment advancements correlated with increased anterior pitch (β = 0.33, 95% CI 0.17-0.49) and outward torque (yaw) (β = 0.81, 95% CI 0.57-1.05) of proximal segments, while superior displacement and anterior pitch correlated with lateral (β = 0.34, 95% CI 0.18-0.49) and medial (β = -0.44, 95% CI -0.62 to -0.25) movements, respectively. Certain cephalometric measures, particularly changes in mandibular width, correlated with translational and rotational movements. In conclusion, current VSP is not fully accurate in predicting postoperative mandibular segment positions. These findings highlight the need for incorporating dynamic segment behaviour into VSP protocols to improve surgical planning accuracy and postoperative outcomes.