Design Modifications of the Twin-Block Appliance: Facial and Dentoalveolar Outcomes in Class II Individuals

Abstract

Objective: This study aimed to evaluate and compare the sagittal and vertical cephalometric changes observed in growing patients with Class II malocclusion and permanent dentition treated with a Modified Twin Block (TBM) with those observed in a historical control group of untreated individuals. Materials and Methods: An observational, comparative, longitudinal, retrospective study was conducted using 240 lateral cephalometric radiographs from 120 individuals with Class II malocclusion and mandibular retrusion relative to the maxilla. The treatment group (TG) comprised 60 patients previously treated with the Modified Twin Block (TBM), aged 11.5–14 years at the initial assessment (T1), whereas the control group (CG) comprised 60 untreated individuals retrospectively selected from historical records in the AAOF Craniofacial Growth Legacy Collection. Two cephalometric records were analysed for each individual (T1 and T2). Eleven cephalometric variables representing the sagittal, vertical, and angular dimensions included in Areas 1, 2, and 5 of the cephalometric protocol were evaluated. Changes were calculated as T2 − T1 and compared between groups for the overall sample and after stratification by sex. The p values for the 33 comparisons were adjusted using the Benjamini–Hochberg procedure to control the false discovery rate. Between-group mean differences, 95% confidence intervals, and effect sizes using Hedges’ g were also calculated. As a sensitivity analysis, linear regression models were fitted adjusting for the corresponding baseline cephalometric value, age at T1, sex, and the duration of the T1–T2 interval, with HC3 robust standard errors. Results: No statistically significant age differences were observed between groups at T1 or T2. However, the T1–T2 observation interval was significantly longer in the control group than in the treatment group (1.80 ± 0.31 vs. 1.65 ± 0.26 years; p = 0.004). After Benjamini–Hochberg correction of the 33 comparisons, statistically significant between-group differences remained for seven variables in the overall sample. In the multivariable sensitivity analysis, after adjustment for the baseline cephalometric value, age at T1, sex, and observation-interval duration, followed by correction for multiple comparisons, differences remained significant for A-N, S-Go, A-Me, N-Me, and ANB. Adjusted TG − CG differences were −1.70 for A-N (95% CI: −2.36 to −1.04), +2.29 for S-Go (95% CI: 1.04 to 3.53), +1.50 for A-Me (95% CI: 0.53 to 2.47), +3.49 for N-Me (95% CI: 2.01 to 4.96), and −1.04° for ANB (95% CI: −1.46 to −0.62). No significant differences were observed in functional occlusal plane inclination. Interaction analyses provided no statistically significant evidence of differences between males and females in treatment-group-associated changes. Conclusions: In growing patients with Class II malocclusion and permanent dentition, TBM treatment was associated with differences in sagittal and vertical cephalometric changes compared with the historical control group. The most consistent findings involved A-N, S-Go, A-Me, N-Me, and ANB and remained significant after multivariable adjustment and correction for multiple comparisons. These results should be interpreted in light of the retrospective, non-randomised design, the use of historical controls, the absence of a homogeneous indicator of skeletal maturation, and the lack of long-term follow-up.