Finite element analysis of the stress state produced by an orthodontic skeletal anchorage system based on miniscrews

Aims: The aim of this work is to produce detailed analysis and quantitative results of the stress state induced in an inferior first molar tooth by an orthodontic mesialization system based on a mini-screw, a bracket, and a rubber elastic string. Materials and Methods: The implant was modeled as a non-osteointegrated Ti-6Al-4V standard mini-screw, implanted in the anterior-buccal region of human jaw. 3D realistic models were constructed using data based on micro-computed tomography scans of human teeth as found in the literature. A couple of self-balanced forces of 4 N was applied and finite element method analysis was run and produced an approximate solution, which allowed to display stress distribution over the whole model. Materials' behavior was assumed elastic and linear. This approximation applies to the 1 st stage of the orthodontic treatments. Results: A detailed qualitative and quantitative analysis of the stress state is presented through images. Results in terms of stresses and displacements were studied to exclude any possibility of bracket debonding, bone failure, and loss of stability of the screw. Results were compared to the ultimate strengths of the bio-materials involved using engineering failure criteria. The actual stress state was found to be lower than the critical values. Conclusion: Results allows to qualitatively see the amount of bone, surronding the mini-screw, and the tooth, that undergoes stress. Furthermore, quantitative analysis of stress could exclude failure in alveolar bone and detachment at the enamel-bracket interface. The applied force and devices were proved to be safe to use for this kind of orthodontic facilities.