Twin Block appliance with acrylic capping does not have a significant inhibitory effect on lower incisor proclination

To investigate the effect of acrylic capping, treatment duration, overjet, and lower incisor inclination on the posttreatment tooth position in patients treated with 2 Twin Block (TB) appliance versions.

Cephalograms of 56 patients with Class II malocclusion (21 boys, 35 girls; mean age before treatment [T1] = 12.5 years; standard deviation, 0.7) treated with a TB appliance with either acrylic capping or ball-ended clasps on lower incisors were retrospectively collected and traced. Lower incisor inclination (L1-GoGn, L1-GoMe, L1-MP) was measured at T1 and after TB appliance removal (T2). Regression analysis was performed to evaluate the effect on the lower incisor inclination of appliance type, overjet, lower incisor inclination at T1, and treatment duration after adjusting for baseline measurements.

Appliance design was not a significant predictor for either incisor inclination measurement (P< .05). Pretreatment lower incisor inclination was the only factor significantly associated with final tooth inclination (L1-GoGn: β = 0.57, 95% confidence interval [CI] = 0.30, 0.84, P < .001; L1-GoMe: β = 0.56, 95% CI = 0.28, 0.84, P < .001; L1-MP: β = 0.46, 95% CI = 0.17, 0.75, P = .003). There was weak evidence that treatment duration excluding L1-MP (95% CI = -1.85, -0.02; P = .045) and overjet might be associated with inclination of lower incisors at T2.

TB appliance design with acrylic capping on lower incisors appears not to significantly control incisor proclination. Pretreatment lower incisor inclination may be significantly associated with tooth inclination after active TB treatment and should be considered in treatment planning.