Effects of miniscrew orientation on implant stability and resistance to failure

Introduction: The purpose of this study was to determine the effect of miniscrew implant orientation on the resistance to failure at the implant-bone interface. Methods: Miniscrew implants (IMTEC, Ardmore, Okla) were placed in 9 human cadaver mandibles, oriented at either 90 degrees or 45 degrees to the bone surface, and tested to failure in pull-out (tensile) and shear tests. The line of applied force and the orientation of the implants aligned at 45 degrees were either parallel or perpendicular to the maximum axis of bone stiffness. In the shear tests, the implants aligned at 45 degrees were angled toward and opposing the axis of shear force. Results: The implants aligned at 90 degrees had the highest force at failure of all the groups (342 +/- 80.9 N; P < 0.001). In the shear tests, the implants that were angled in the same direction as the line of force were the most stable and had the highest force at failure (253 +/- 74.05 N; P < 0.001). The implants angled away from the direction of force were the least stable and had the lowest force (87 +/- 27.2 N) at failure. Conclusions: The more closely the long axis of the implant approximates the line of applied force, the greater the stability of the implant and the greater its resistance to failure. (Am J Orthod Dentofacial Orthop 2010; 137:91-9)