Effect of mini-screw maximum insertion torque on skeletal orthodontic anchorage

Objective. The primary objective of this study was to examine the effect that maximum insertion torque has on force resistance and stability of titanium screws in cadaver maxillae and mandibles.Materials and Methods. Forty-eight cadaver maxillary and mandibular jaw quadrants were obtained Two titanium mini-screws were placed in each jaw quadrant and maximum insertion torque was measured. Each mini-screw was subjected to tangential force application oriented perpendicular to placement of the mini-screw and parallel to the occlusal plane. The force applied at each deflection was measured up to 1.5mm, but only the first 0.60mm of movement was investigated. This amount of displacement was selected to represent the amount of movement that would result in a clinically mobile mini-screw and potential failure.Results. The post-hoc Tukey-Kramer's test showed that mean anchorage resistance for screws placed with maximum insertion torque of less than 5Ncm was significantly lower than those observed for 5-10Ncm and greater than 10Ncm. No significant difference was found between 5-10Ncm and greater than 10Ncm.Conclusions. In vitro, mean anchorage resistance for screws placed with maximum insertion torque of less than 5Ncm was significantly lower than those placed with maximum insertion torque between 5Ncm and 10Ncm at deflections ranging from 0.12mm to 0.60mm. In terms of maximizing anchorage resistance, we recommend placement of orthodontic mini-screws with maximum insertion torque of greater than 5Ncm.