Balancing the Load: How Optimal Forces Shape the Longevity and Stability of Orthodontic Mini-Implants

Abstract

Objective: This study aims to investigate the mechanical behavior of titanium (Ti6Al4V) mini-implants (MIs) under varying orthodontic forces using finite element analysis (FEA) and to evaluate their performance and durability under realistic clinical conditions. Optimal orthodontic forces significantly influence the structural integrity and functional longevity of MIs while minimizing adverse effects on surrounding bone tissues. Materials and Methods: A commercially available MI (diameter: 2.0 mm, length: 12 mm) was modeled using FEA. The mandible geometry was obtained using computed tomography (CT) scanning, reconstructed in 3D using SpaceClaim software 2023.1, and discretized into 10-node tetrahedral elements in ANSYS Workbench. Material properties were assigned based on the existing literature, and the implant-bone interaction was simulated using a nonlinear frictional contact model. Orthodontic forces of 2 N and 10 N, inclined at 30°, were applied to simulate clinical loading conditions. Total displacement, von Mises stresses, equivalent strains, fatigue life, and safety factors were analyzed to assess the implant's mechanical performance. Results: At 2 N, the MI demonstrated minimal displacement (0.0328 mm) and sustained approximately 445,000 cycles under safe fatigue loading conditions, with a safety factor of 4.8369. At 10 N, the implant's lifespan was drastically reduced to 1546 cycles, with significantly elevated stress (6.468 × 10⁵ MPa) and strain concentrations, indicating heightened risks of mechanical failure and bone damage. The findings revealed the critical threshold beyond which orthodontic forces compromise implant stability and peri-implant bone health. Conclusions: This study confirms that maintaining orthodontic forces within an optimal range, approximately 2 N, is essential to prolong MI lifespan and preserve bone integrity. Excessive forces, such as 10 N, lead to a rapid decline in durability and increased risks of failure, emphasizing the need for calibrated force application in clinical practice. These insights provide valuable guidance for enhancing MI performance and optimizing orthodontic treatment outcomes.

Keywords: cortical bone; finite element method (FEM); fracture; mini-implant; orthodontic forces; stress distribution.

Figure 1

Workflow for finite element modeling of an orthodontic MI and adjacent bone structures: (a) Commercially available titanium MI, diameter 2 mm, was modeled using the finite element method; (b) Geometry of the mandible: CT scan image in STL format; (c) The global 3D geometric model discretized into finite elements (left) and the zoomed-in discretized model at the location of interest (right, MI and the adjacent orthodontic anchorage area).

Figure 2

Results for the mini-implant under 2 N loading at 30°: (a) Total deformations; (b) von Mises equivalent stresses; (c) Equivalent strains; (d) The mini-implant was fractured after removal precisely in the area where the FEM analysis indicated the maximum von Mises stress.

Figure 2

Results for the mini-implant under 2 N loading at 30°: (a) Total deformations; (b) von Mises equivalent stresses; (c) Equivalent strains; (d) The mini-implant was fractured after removal precisely in the area where the FEM analysis indicated the maximum von Mises stress.

Figure 3

Safety factors obtained for the mini-implant under an applied force of 2 N: (a) Safety factors σc/σMax; (b) Safety margin (σc/σMax) − 1; (c) Stress ratio σMax/σc.

Figure 4

Results obtained for mini-implant endurance under a force of 2 N: (a) Endurance; (b) Failure; (c) Fatigue safety factors.

Figure 5

Results obtained for mini-implant endurance under a force of 10 N: (a) Endurance; (b) Failure; (c) Fatigue safety factors.