Torque Analysis of Self-drilling Mini-screws placed with and without a Pilot Drill: A Canine Study

Purpose: The use of temporary anchorage devices (TADs), such as mini-screws, palatal implants and mini-plates, has become a popular treatment option in orthodontics. The objectives of this study were: (1) to compare the success rates of self-drilling mini-screws placed with or without use of a pilot drill, (2) to evaluate the implant placement torque (IPT) of self-drilling miniscrews and (3) to measure the removal torque of self-drilling mini-screws. materials and methods: Six American foxhounds served as subjects in this study. Three OsteoMed self-drilling mini-screws (1.6 mm diameter and 8 mm length) were planned to be placed in each side of the mandible between the roots of the teeth canine/premolar 1 (PM1), PM2/PM3 and PM3/PM4. The sites were allocated randomly in: (1) control group—mini-screws placed with pilot drill and (2) test group—mini-screws placed without pilot drill (self-drilling). The implant placement torque (IPT) and the number of turns performed by the mini-screws during placement were measured. After a healing period of 6 weeks, the mini-screws were removed, and the removal torque was measured. Results: A total of 33 mini-screws were placed in six animals. After 6 weeks, the success rate for the control and test groups were 46.7 and 80% respectively (difference not statistically significant). There was no statistically significant difference in the terminal mean IPT values and the mean number of turns for failed and successful mini-screws. The difference between the mean IPT values at the 3rd turn during mini-screw placement in the successful and failed mini-screws (5.56 and 14.03 Ncm respectively) was statistically significant (p < 0.01). Conclusion: There was no statistically significant difference in the success rate between self-drilling mini-screws that did or did not have osteotomies (46 vs 80% respectively). However, the IPT at the third revolution for successful mini-screws averaged 5.56 Ncm (p < 0.01).