The Effect of Time on Orthodontic Mini-Screw Implants Stability (An experimental study)

Background: Mini-screw implants have become an accepted and reliable method for providing orthodontic anchorage. The present study aimed to measure the primary and secondary stability of mini-screw implants using the removal torque value as indictor for the stability and comparing between four different periods of mini-screw implants removal (Immediate, 2 weeks, 4 weeks and 6 weeks). Materials and Methods: Forty mini-screw implants, all of the same manufacture, length (7 mm), diameter (1.4 mm) and of cylinder type, were implanted in the tibia bone of two sheep (ten in each tibia) after anesthesia and flap reflection using drilling burs. The insertion torque were standardized and equalized for all mini-screws. Mini-screw implants were removed after different periods of time (immediately, 2 weeks, 4 weeks and 6 weeks) using digital torque screw driver (DID-4). One-way ANOVA test was used to compare among the groups. Results: The results showed that mini-screw implants stability significantly decreased during the first two weeks then started to increase during the four and six weeks. Conclusions: It was concluded from this study that mini-screw implants stability is affected by the period of implantation, decreased during the first two weeks and then started to increase.