Finite Element Analysis of TAD Screw Stability in the Mandible: Effects of Marginal Bone Loss and Bone Quality

Rajaeirad, Mohadese; Jamshidi, Nima

Abstract

This study uses finite element method (FEM) analysis to assess the impact of marginal bone loss (MBL) and bone quality (BQ) on temporary anchorage device (TAD) screw stability, placed between mandibular teeth 4 and 5 per orthodontic guidelines. A 2 N orthodontic force was applied, with micromotion as the stability metric. Five BQ groups were modeled—very strong, strong, normal, weak, and very weak —with Young’s modulus varied by ±15% per group and Poisson’s ratio fixed at 0.3. Five MBL groups were simulated with cortical bone thickness at 1, 1.5, 2, 2.5, and 3 mm. Simulations revealed that reducing cortical thickness from 3 mm to 1 mm increased micromotion by 40% (from 8 µm to 11.2 µm). Similarly, decreasing Young’s modulus from 19.55 GPa (very strong) to 10.2 GPa (very weak) elevated micromotion by 32% (from 8 µm to 10.56 µm) under identical loads. These findings highlight cortical thickness and BQ as key predictors of TAD stability, guiding orthodontic planning. High-resolution imaging is recommended to optimize TAD placement and mitigate MBL-related complications. This FEM framework elucidates mandibular biomechanical interactions.

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