Effects of placement angle and direction of orthopedic force application on the stability of orthodontic miniscrews.

OBJECTIVES: To evaluate the influence of placement angle and direction of orthopedic force application on the stability of miniscrews. MATERIALS AND METHODS: Finite element analysis was performed using miniscrews inserted into supporting bone at angles of 90 degrees , 60 degrees , and 30 degrees (P90 degrees , P60 degrees , and P30 degrees ). An orthopedic heavy force of 800 gf was applied to the heads of the miniscrews in four upward (U0 degrees , U30 degrees , U60 degrees , U90 degrees ) or lateral (L0 degrees , L30 degrees , L60 degrees , L90 degrees ) directions. In addition, pull-out strength of the miniscrews was measured with various force directions and cortical bone thicknesses. RESULTS: Miniscrews with a placement angle of 30 degrees (P30 degrees ) and 60 degrees (P60 degrees ) showed a significant increase in maximum von Mises stress following the increase in lateral force vectors (U30 degrees , U60 degrees , U90 degrees ) compared to those with a placement angle of 90 degrees (P90 degrees ). In accordance, the pull-out strength was higher with the axial upward force when compared to the upward force with lateral vectors. Maximum von Mises stress and displacement of the miniscrew increased as the angle of lateral force increased (L30 degrees , L60 degrees , L90 degrees ). However, a more dramatic increase in maximum von Mises stress was noted in P30 degrees than in P60 degrees and P90 degrees . CONCLUSION: Placement of the miniscrew perpendicular to the cortical bone is advantageous in terms of biomechanical stability. Placement angles of less than 60 degrees can reduce the stability of miniscrews when orthopedic forces are applied in various directions.