Optimized Orthodontic Palatal Miniscrew Implant Insertion Angulation: A Finite Element Analysis

There is a controversial body of evidence regarding optimal insertion angulation of an orthodontic miniscrew as a mean of skeletal anchorage.A bracket head-type 8-mm-long miniscrew (60-degree symmetrical trapezoid thread, 0.1-mm thread fillet, 0.2-mm thread height, with 0.5-mm thread pitch) was designed and monocortically inserted at 30, 45, 55, 70, 90, 110, 125, 135, and 150 degrees of inclination to the surface of bone. A bilayer cortical (1.6 mm) and cancellous (8.5 mm) bone model was constructed, adopted from a 22-year-old male patient's cone beam computed tomography (CBCT) image of his anterior hard palate area. A horizontal force of 2 N was applied parallel to the bone surface. Bone material was simulated as normal and osteoporotic bone. The maximum equivalent von Mises stress and microstrain values were separately calculated for the miniscrew, cortical bone, and cancellous bone. Deflections of the whole bone and miniscrew were also reported.A significant lower stress was found in the cancellous bone compared to the cortical bone. Osteoporotic bone displayed higher strain values. Overall, 30-degree models exhibited the lowest von Mises stress and strain values for the cortical layer and miniscrew in both normal and osteoporotic models. Meanwhile, 90-degree models displayed the lowest strain values in the osteoporotic and normal cancellous bones. Minimum bone and miniscrew deflection values were related to the model of 30-degree insertion angulation.These results showed that, within the limitations of the study, the 30-degree angulation of miniscrew insertion toward the direction of applied force could lower the cortical bone stress and strain.