# Biomechanical Influence of Placement Angle and Loading Direction of Orthodontic Miniscrews on Orthotropic Mandible

## TL;DR

This study examines how the angle and direction of orthodontic miniscrew placement affect their stability in bone with directional mechanical properties.

## Contribution

The study introduces orthotropic bone modeling to better understand miniscrew biomechanics, revealing limitations of isotropic assumptions.

## Key findings

- Orthotropic modeling shows higher displacement and instability compared to isotropic modeling.
- Oblique insertion at 60° increases strain and reduces osseointegration potential.
- Stress and strain distributions are symmetric, allowing prediction of biomechanical responses from partial data.

## Abstract

FEA of orthodontic miniscrews has predominantly assumed isotropic, homogeneous bone, neglecting directional variations in mechanical properties. This study investigated the biomechanical behavior of miniscrews under different insertion angles and loading directions using both isotropic and orthotropic mandibular bone models. The results indicated that isotropic modeling may underestimate miniscrew displacement and associated instability, whereas orthotropic material properties better reflect the true mechanical response of bone. Oblique insertion at 60° (U60°) led to higher strain and greater variability, which may compromise osseointegration; aligning the loading direction parallel to the insertion plane is therefore recommended when oblique placement is unavoidable. Screw thread design had minimal influence on displacement, von Mises stress, or bone strain during vertical insertion. Stress and strain distributions exhibited symmetry, suggesting that analyzing partial loading directions can predict the overall biomechanical response. All predicted values remained below bone and material strength limits, confirming the mechanical safety of the current miniscrew design under a 2 N load. Implant failure is likely attributable to poor osseointegration or inflammation rather than structural limitations.