Effects of force magnitude on torque control in the correction of bimaxillary protrusion with mass retraction.

Abstract

OBJECTIVES:This study was designed to explore whether force magnitude would influence incisor torque control and the overall outcome in patients with bimaxillary protrusion who need mass incisor retraction.MATERIALS AND METHODS:Forty-one female patients (aged > 15 years) with bimaxillary protrusion requiring mass incisor retraction were selected. Two sliding mechanics were utilized, with the elastic group receiving a light force of ~100 g by wearing elastics and the power chain group receiving a moderate force of ~250 g by power chain. Lateral cephalograms obtained before and after treatment were traced and measured.RESULTS:Patients in both groups displayed maxillary protrusion with a similar skeletal class II tendency. A longer treatment time was found in the elastic group. No difference in the distance of incisor tip movement was observed between the two groups; however, a larger inclination of upper incisors was found in the elastic group, indicating less loss of torque. In addition, larger reduction in Sella-Nasion-A and A-Nasion-B angle was observed in the elastic group, which was accompanied by a larger ratio of upper lip retraction to upper incisor retraction as well as more upper lip retraction.CONCLUSIONS:Sliding mechanics with elastics to generate light forces can achieve better torque control with more reduction in skeletal and soft tissue protrusion.