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

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). 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 fi rst 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 signifi cance was set on 0.05. The paired t-test for maximum insertion torque (MIT) showed that MIT1 was signifi cantly lower than other MIT values (P = 0.02) and also MIT2 was signifi cantly higher than MIT5 (P = 0.01), but other MIT values had no signifi cant differences. The paired t-test for maximum removal torque (MRT) showed that only MRT2 was signifi cantly higher than other MRT values (except MRT1) (P = 0.046). Regarding FT, the t-test showed that there was no signifi cant difference between FT0 and FT5 (P = 0.485). Within limitations of this study, fi ve time insertion, cleaning, processing and steam sterilization had no signifi cant negative effect on insertion, removal and FT of the mini screws.