Hard and Soft Tissue Factors Associated With Changes in the Buccal Corridor Area Ratio After Orthognathic Surgery

BackgroundThe smile is a complex composite phenotype of hard tissue and perioral soft tissue characteristics.However, the factors associated with postoperative changes in the buccal corridor area ratio (BCAR), which standardizes the buccal corridor area relative to the total smile area enclosed by the inner borders of the lips, remain unclear.Therefore, this study explores the hard tissue and soft tissue factors associated with changes in the BCAR after orthognathic surgery. Materials and methodsThis single-center, retrospective, observational study evaluated 27 patients who underwent orthognathic surgery.Smile-related, skeletal, dental, and soft tissue parameters were measured using standardized frontal posed-smile photographs, lateral cephalometric radiographs, and cone-beam computed tomography (CBCT) images obtained immediately before surgery (T0) and approximately six months postoperatively (T1) to calculate the pre-to-postoperative changes (Δ= T1 -T0).Univariable correlation analysis and stepwise multiple linear regression analysis were performed, with the change in BCAR (ΔBCAR) designated as the dependent variable. ResultsΔBCAR was 0.0030 ± 0.0170.In Model 1, the ΔSmile Index was significantly associated with ΔBCAR (B = 0.004, β = 0.539, p = 0.004; R² = 0.291, adjusted R² = 0.262).In the final stepwise regression model, the ΔSmile Index (B = 0.004, β = 0.510, p = 0.001) and change in point A-nasion-point B angle (ΔANB; B = -0.002,β = -0.479,p = 0.003) were selected as variables statistically associated with ΔBCAR (R² = 0.519, adjusted R² = 0.479).The variance inflation factor (VIF) for both variables was 1.004. ConclusionsPostoperative changes in BCAR were statistically associated with changes in the Smile Index and ANB angle in this exploratory cohort.However, the association involving the Smile Index may partly reflect changes in vertical smile opening and their influence on TSA, the denominator of BCAR.These findings do not establish an independent biological relationship, causality, or individual predictive ability and should be interpreted as hypothesis-generating.