Mechanical properties of self-drilling orthodontic micro-implants with different diameters

Objective: The hypothesis to be tested is that peak-insertion torque of self-drilling micro-implants of an appropriate diameter correlates with peak-removal torque mechanically. Materials and Methods: A total of 360 self-drilling micro-implants composed of five different types were used. They (24 of each group) were inserted in three types of artificial bone with the use of a driving torque tester at a speed of 15 rpm. Insertion torque was measured during the placement, while the removal torque was measured within 3 days after insertion. Results: Most of the micro-implants in type A sheared before they were completely inserted in 40 pounds per cubic foot bone. The implants in other types were successfully inserted without implant breakage and bone fracture in all bone densities. There was a statistically significant correlation between insertion torque and removal torque (r >= 0.43543, P = .0001). There were significant differences in insertion and removal torque among the diameters of implants and bone densities with an increasing tendency. The torque loss rates reduced as the diameter of the implant and bone density increased. Conclusions: Micro-implants with a diameter of less than 1.3 mm are unsuitable for insertion into a bone with a density greater than 40 pounds per cubic foot mechanically when one is using a self-drilling technique. (Angle Orthod. 2010;80:821-827.)