3D lip changes in skeletal Class III patients with premolar extraction: A prospective cohort study comparing surgery-first and orthodontics-first approaches

Objective To investigate the three-dimensional (3D) changes in lip morphology introduced by different surgical orthodontic treatment approaches in skeletal Class III patients. Methods Forty Class III patients were treated using the surgery-first approach (SFA, n = 20) or a three-stage approach (TSA, n = 20), both involving bimaxillary surgery and maxillary premolar extractions. Cephalograms and facial scans were obtained at different time points (T0–T5) throughout the treatment period. T tests and repeated measures analysis of variance were compared to 3D lip morphology between groups. Correlation analysis and stepwise linear regression were used for prediction. Results After debonding, mandibular incisors in the SFA group were positioned more lingually (L1MP: SFA 80.75 ± 5.73°, TSA 89.78 ± 5.88°, P < 0.001), and the smaller ANB values (SFA 1.04 ± 1.43°, TSA 2.19 ± 0.99°, P = 0.005). Upper vermilion length increased in both groups after debonding, while lower vermilion length decreased significantly. The lower vermillion length in the SFA group was shorter than that in the TSA group (SFA 8.66 ± 2.01 mm, TSA 10.35 ± 2.19 mm, P = 0.015). ΔU1-AP, ΔANB, and ΔWits were significantly correlated with 3D lip morphology changes. Conclusions Both methods significantly improved the aesthetics of lip morphology in skeletal Class III patients. When the extraction space was closed, the lip shape was nearly stable in the SFA; TSA was stabilized 6 months post-surgery. The lips exhibited a compensatory response to differences in hard tissue and showed a moderate association with changes in dental and skeletal measurements.