A Retrospective Study on the Cephalometric Markers That Predict the Treatment Outcomes of Twin Block Functional Appliance

Background: Despite the widespread use of functional appliances, broad variations are reported on the treatment response. This retrospective study aims to investigate the pre-treatment cephalometric predictors on the treatment outcome of Twin block in growing patients with class II malocclusion Methods After screening, a total of 90 patients treated by Twin block were included in the study. The treatment outcome was the advancement of the chin position, assessed by the distance of skeletal pogonion to the vertical reference plane perpendicular to Frankfurt plane (△Pog-VRP). Moreover, △Pog-VRP is adjusted by facial growth evaluated by △N-Ba to minimize the growth discrepancy among individuals (adj△Pog-VRP). The pre-treatment cephalometric measurements were compared with independent t -test. Stepwise multivariate regression analysis was performed to determine the pre-treatment cephalometric predictors for the treatment outcome. Results Patients were equally divided into good response group (GRG/adjGRG, N = 45) and poor response group (PRG/adjPRG, N = 45) respectively based on the median value of △Pog-VRP/adj△Pog-VRP. Patients with greater chin advancement had a significantly reduced cephalometric measurements in the vertical dimensions including ∠Na-Go-Me, ∠MP-OP and sum of angels ( P  < 0.05). And such differences increased after adjustments in comparison between adjGRG and adjPRG. Importantly, ∠Na-Go-Me was found to be independent predicter on Pog advancement before (β=-0.26, 95%CI, -0.06 to -0.01, P  = 0.01) and after adjustments (β=-0.29,95%CI -0.06, -0.01, P < 0.01). Conclusion With the limitation of the study, we provide evidence that patients with a smaller Na-Go-Me angle are more likely to experience a greater chin advancement following Twin block treatment.