Three-dimensional soft tissue and cephalometric analysis for Class II malocclusion with Twin-Block appliance treatment

Background To evaluate the dentoskeletal and 3D soft tissue changes induced by Twin-Block appliances in adolescents with Class II Division 1 malocclusion, and to assess short-term treatment stability via 3D facial scanning. Materials and Methods Fifty-six patients with Class II division 1 malocclusion (mean age: 9.60 ± 1.16 years) undergoing Twin-Block treatment at University Stomatological Hospital from November 2023 to March 2025. After diagnosis and analysis, patients who needed Twin-Block orthopedic treatment underwent three-dimensional facial scanning (Artec Space Spider) and cephalometric lateral radiography. Pre-treatment (T0), post-treatment (T1), 3-month (T2), and 6-month (T3) data were collected using 3D facial scanning (Artec Space Spider) and lateral cephalography. Soft tissue and skeletal parameters were measured, with statistical analysis performed via paired t-tests and Wilcoxon tests. Results Cephalometric analysis revealed significant post-treatment changes: SNB angle increased ( P  < 0.01), ANB angle decreased ( P  < 0.01), mandibular ramus/body lengths (Ar-Go, Go-Pog) and facial heights (ANS-Me, N-Me) increased (P < 0.01). Overjet reduced by 3.18 mm ( P  < 0.01), and upper incisor inclination (U1-SN) decreased by 3.9° ( P  < 0.01). 3D facial analysis showed statistically significant soft tissue changes at T1: alae nasi width (+ 0.43 mm, P  < 0.01), upper/lower lip lengths (+ 0.50 mm, + 0.93 mm, P  < 0.01), mentolabial angle (+ 9.89°, P  < 0.01), and reduced upper lip-chin convexity ( P  < 0.01). At 3-month follow-up, no significant soft tissue regression was observed ( P  > 0.05). At the 6-month follow-up, significant differences were observed in the upper/lower lip to chin convex angle (P < 0.01). Statistically significant differences were also found in the width of the nasal alar, the width of the nasal base, the width of the philtrum, and the mentolabial angle (P < 0.05). Overlap analysis of the three-dimensional model showed that the corresponding landmarks produced different degrees of displacement in the vertical and sagittal directions, respectively. Conclusions Twin-Block treatment effectively improves occlusal relationships, promotes mandibular growth, and enhances soft tissue aesthetics by reducing lip protrusion and optimizing chin-lip-nose harmony. 3D scanning demonstrates high reliability in quantifying soft tissue remodeling. Short-term stability (3 months and 6 months) highlight Twin-Block’s efficacy in adolescent Class II correction, with implications for early orthopedic intervention. Trial registration: This study was registered at the Chinese Clinical Trial Registry (ChiCTR2300077826) on November 21, 2023.