Can maxilla and mandible bone quality explain differences in orthodontic mini-implant failures?

Area of Science:

• Orthodontics
• Biomaterials Engineering
• Finite Element Analysis

Background:

• Orthodontic mini-implants (OMIs) are crucial for anchorage in orthodontic treatment.
• Clinical success rates for OMIs are higher in the maxilla than mandible, despite the mandible's denser bone.
• Finite element analysis (FEA) can model OMI biomechanics and predict failure risks.

Purpose of the Study:

• To compare the risk of orthodontic mini-implant (OMI) failure between the maxilla and mandible using FEA.
• To investigate the influence of bone density and applied forces on OMI stability.
• To reconcile the clinical observation of higher OMI success in the maxilla with biomechanical data.

Main Methods:

• Development of four 3D finite element models simulating OMIs in low-density maxilla, control maxilla, control mandible, and high-density mandible.
• Application of horizontal forces (2N clinical, 10N overload) to simulate anterior retraction.
• Evaluation of OMI displacement and major principal bone strains to assess primary stability and resorption risk.

Main Results:

• OMI displacement remained below critical thresholds (50-100 µm) in all models, indicating sufficient primary stability.
• The maxilla demonstrated a higher susceptibility to instability under overload conditions.
• Low-density maxilla models showed bone strains exceeding the 3000 µstrain threshold for pathologic resorption during overload.

Conclusions:

• Bone quality alone does not fully explain the observed differences in OMI failure rates between the maxilla and mandible.
• Finite element analysis suggests overload conditions in the maxilla, especially in lower density bone, increase failure risk.
• Residual stress from OMI insertion, not accounted for in this FEA, may be a critical factor influencing clinical outcomes.