An evaluation on the effect of the MIR appliance on the force resistance and stability of mini screws of different lengths and diameters

The present study aims to investigate the effect of the mini-implant ring (MIR) appliance on force resistance and stabilization when used in vitro with mini screws of different lengths and diameters. A total of 120 TM (Trimed, Ankara, Turkey) mini screws, including 20 pieces of 1.4 mm diameter and 6 mm length, 20 pieces of 1.4 mm diameter and 8 mm length, 20 pieces of 1.6 mm diameter and 6 mm length, 20 pieces of 1.6 mm diameter and 8 mm length, 20 pieces of 1.8 mm diameter and 6 mm length, and 20 pieces of 1.8 mm diameter and 8 mm length were used for the study. Titanium TM mini screws with a conical structure and "self-drilling" feature were preferred in the study. The other group in which the MIR was not applied was used as the control group. Mini screws were applied to samples obtained from bovine hip bones, in the laboratory using a torque screwdriver (N2DPSK, Nakamura MFG Co Ltd, Tokyo, Japan) and maximum application torque (MAT) values were measured. Then, by applying force perpendicular to the long axis of the mini screw with an Instron tester, the resistance values of the mini screws up to a 0.6 mm displacement were recorded. Following the evaluation of the mobility of the force-tested mini screws, the mini screws were removed from the bone by measuring their maximum extraction torques (MET) with a torque meter screwdriver. The statistical analysis showed that application torques increased in mini screws to which the MIR appliance was applied, and this increase did not exceed desired levels. A nonsignificant increase in extraction torques was also recorded. These results show that the MIR apparatus is effective in increasing the force resistance and stability particularly of smaller diameter mini screws to a certain extent. As a result of the research, the MIR apparatus is recommended as a good option, especially in cases where the cortical bone is thin or a smaller diameter mini screw is preferred, since it increases the primary stability and force resistance of the mini screw. Keywords: Mini screw, MIR appliance, stability, force resistance, screw diameter, screw length