Effect of Change Angulation and Material of Mini-screw Inserted in Retromolar Pad Area on Stress Distribution: A Finite Element Simulation Study

This study evaluated the influence of angulation and material composition on the stress distribution and displacement of mini-screws placed in the retromolar pad area using finite element analysis; these mini-screws inserted in the retromolar pad area were referred to as MRM. A 3D mandible model was generated from CT scan data using Mimics and 3-Matic software, while the mini-screw was modelled in AutoCAD. Finite element analysis was performed with Inventor Professional software. A 2 N force, parallel to the occlusal reference line (ORL), was applied to MRM at insertion angles of 0°, 15°, 30°, 45°, and 60° relative to the ORL. Three MRM materials were analysed: stainless steel (SS), titanium alloy (Ti-6Al-4V), and pure titanium (Ti). Results revealed that the lowest Von Mises stresses occurred at a 0° insertion angle, while the highest stresses were observed at 60°. Stress levels were comparable across materials at 0°, 15°, and 30°, but SS MRM generated higher stresses than titanium materials at 45° and 60°. Displacement analysis indicated that SS MRM had the lowest displacement, while Ti MRM exhibited the highest across all angles. Importantly, all stress values remained below the bone’s yield strength, and displacements were clinically insignificant. For optimal stability, a 0° insertion angle is recommended, with 15° and 30° serving as viable alternatives. These findings provide guidance on selecting mini-screw angulation and materials for effective orthodontic anchorage in the retromolar pad area.