The comparison of insertion torque and stability values of four different orthodontic mini-screws

The purposes of this in-vitro study were to analyze and to compare the insertion torque and stability values of four different sizes of orthodontic mini-screws with two different insertion angles. In this study, a total of 160 mini-screws, including 20 mini-screws in each group, with four different sizes (1.6x8, 1.6x10, 2.0x8, 2.0x10) and two different insertion angles (70 and 90 degree) were inserted into the ilium bone segments of bovine. During placement, maximum insertion torque values of all mini-screws were measured with the use of a torque screw driver (Checkline TSD 50, USA). Then, mini-screws placed at two different angles of 70 degree and 90 degree to force applications in two different directions through a lateral displacement of 1.5 mm of the mini-screw using the Testometric (M500, 25kN; Testometric, Rochdale, Lancashire, England) test machine and force resistance values were measured and recorded until 1.5 mm displacement occured. The maximum insertion torque and force resistance values of all groups were recorded and compared. The data were analyzed with SPSS 17 program. Maximum insertion torque and force resistance values of mini-screws inserted at the angle of 70 degree were significantly higher than maximum insertion torque and force resistance values of mini-screws inserted at the angle of 90 degree (p˂0.001). The results of this study revealed that, the diameter, length and insertion angle of mini-screws have significant effect on the maximum insertion torque and force resistance values. The effects of diameter and angle on the stability of mini-screws are greater than the effects of the length