The effect of multiple processing and re-use on orthodontic mini-screw torque values

BACKGROUND: Reusing orthodontic mini-screws would reduce treatment cost and lead to more use of mini-screws and improvement of orthodontic treatments. This study has assessed the effects of reprocessing and reusing the titanium mini-screws on their maximum insertion, removal and fracture torque (FT). MATERIALS AND METHODS: In this experimental study, 20 titanium mini-screws (1.6-mm × 8-mm) were randomly divided into two equal groups. In the test group, the screws were first sterilized by autoclave and then their FT was assessed. In the control group, FT was assessed after 5 times of insertion, cleaning, processing (37% phosphoric acid for 10 min, 5.25% sodium hypochlorite for 30 min) and sterilizing with autoclave. The maximum insertion and removal torque values were compared using the repeated measure ANOVA and the FT data were analyzed by the t-test. The data were analyzed using the SPSS software (version 13.0) and the significance was set on 0.05. RESULTS: The paired t-test for maximum insertion torque (MIT) showed that MIT(1) was significantly lower than other MIT values (P = 0.02) and also MIT(2) was significantly higher than MIT5 (P = 0.01), but other MIT values had no significant differences. The paired t-test for maximum removal torque (MRT) showed that only MRT(2) was significantly higher than other MRT values (except MRT(1)) (P = 0.046). Regarding FT, the t-test showed that there was no significant difference between FT(0) and FT(5) (P = 0.485). CONCLUSION: Within limitations of this study, five time insertion, cleaning, processing and steam sterilization had no significant negative effect on insertion, removal and FT of the mini-screws.