Lower incisor stability following orthodontic treatment using a fixed spring induced appliance (FSIA)
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Objective: To evaluate the position of the lower incisors in subjects with different facial patterns following use of a fixed spring induced appliance (FSIA) and full fixed multi-banded/bonded orthodontic therapy (FMB treatment). Materials and Methods: A retrospective sample of 115 subjects exhibiting class II malocclusions was used. Subjects were categorized into three growth types according to pre-treatment cephalometric variables (MP-SN and Y-axis), which yielded 28 brachycephalic, 54 mesocephalic, and 31 dolichocephalic subjects. An ANOVA test statistic was used to investigate the differences between the three facial groups. Lateral cephalograms were taken at initial treatment (T0), post-FSIA treatment (T1) & end of active FMB treatment (T2). Results: Dental changes induced by the FSIA & FMB treatment (T2-T0) included: retroclination of the lower incisors (L1-MP: 1.7°±0.9, L1-APo: 3.4°±0.8, L1-NB: 2.2°±0.9), retrusion of the lower incisors (L1-APo: 1.7mm±0.3, L1-NB: 0.2mm±0.06), reduction in the overjet (4mm±0.2) and the overbite (2.8mm±0.3). Facial patterns were not significantly influenced by the FSIA and FMB treatment (MP-SN: 1.8°±0.6; Y-Axis: 0.9°±0.5). Reduction of the skeletal Class II relationship was represented by a significant decrease (p<0.05) of the Wits value (2.3mm±0.2) in all three groups. Lower incisor angular and linear changes at T2 were all proclined and protruded to the initial values at T0. Conclusions: The lower incisors at the end of treatment (T2) remained within normal cephalometric values. The overall change in the position of the lower incisors was proclination and protrusion at T2-T0 and retroclination and retrusion at T2-T1. When T2-T0 was compared, the lower incisors were proclined and protruded to their original position. Facial growth pattern appeared to be unrelated to the amount of dental movement and there was a trend for more pronounced dental retroclination and retrusion of the lower incisors in brachycephalic patients.