Torque ratio as a predictable factor on primary stability of orthodontic miniscrew implants.

OBJECTIVE: To evaluate the torque ratio (TR) as a predictable factor on primary stability of orthodontic miniscrews.

DESIGN: Fifty-eight orthodontic patients (17 men, 41 women; mean age, 21.9 years) with a total of 112 titanium miniscrews of 3 different diameters were subjected. Maximum insertion torque (MIT) and maximum removal torque (MRT) were measured by a digital torque checker at the screw placement. Four weeks after the placement, the stable screw was recorded as a success. Multiple logistic regression analysis was performed to estimate the influence of each clinical variable on success.

RESULTS: Success rates were 82.1% to 89.5%, and there were no significant differences in the 3 types of miniscrews. MIT and MRT showed a positive correlation but did not affect the success rates of miniscrews directly. On the contrary, TR was significantly higher in the success group than in the failure group. In multiple regression analysis, age, TR, and screw proximity had a significant influence on the miniscrew success.

CONCLUSIONS: TR might be related with the miniscrew success rates, and it can be used as a predictable factor on primary stability of orthodontic miniscrew implants. Miniscrew implants should be replaced if MRT is significantly lower than MIT at placement surgery.