歯科矯正用アンカースクリュー埋入時の安定性に関する生体力学的研究

Objective: The purpose of this study was to evaluate the influence of placement angle and force direction on the primary stability of orthodontic miniscrews by analyzing a novel threedimensional finite element model (FEM) approximating the interface between the screw and surrounding bone.
Materials and Methods: Three-dimensional finite element models were made with 6-mm-long miniscrews in diameters of 1.2 mm. Four insertion angles ranging from 0̊ (perpendicular to the bone surface) to 45̊ were examined. A load with 2 N was applied to the center of the screw head in four directions (upward, downward and on the right and left sides).
Results: For miniscrews at the same insertion angle, the stress was the highest (or lowest) under the downward (or upward) force condition. The stress increased as the insertion angle increased, except under the upward force condition. An analysis of the stress distribution in the surrounding bone showed that the most of the stress was absorbed in the cortical bone.
Conclusions: The stress distribution around the miniscrew and surrounding bone during the application of orthodontic force is closely related to the force direction, and insertion angle.