Response of the maxillary dentition to a statically determinate one-couple system with tip-back mechanics: A prospective clinical trial

Objective: To quantify the effects of tip-back mechanics on the maxillary first molars and incisors. Materials and Methods: Sixteen subjects with Class II end-on malocclusion were treated with an intrusion arch to achieve distalization of the maxillary molar through tip-back mechanics. Lateral cephalograms were taken prior to molar tip-back (T1), after molar tip-back (T2), and after molar root uprighting (T3). Data were analyzed using the Friedman's and Wilcoxon signed rank tests to evaluate differences in time points (P <= .016). Results: The maxillary first molar distalized 1.53 mm (P = .001) with 6.65 degrees (P =.001) of distal tipping and 0.86 mm (P = .001) of extrusion at T2. Minor relapse of the first molar (mesial direction) was seen at T3. The maxillary incisors flared labially 0.4 mm, and the incisor root apex moved palatally 1.19 mm (P = .005) at T2. At T3, the incisor root apex moved palatally 1.5 mm (P = .003) from T1. An angular change from T1 of 3.310 degrees (P = .008) and 3.53 (P = .014) was seen at T2 and T3, respectively, as a result of palatal root movement of the maxillary incisors. Conclusions: A significant amount of distalization of maxillary molars was attained at the crown level with tip-back mechanics. Palatal root angulation change was significant in the incisors with minimal anteroposterior movement of the incisal edge.