Teeth with external apical root resorption under orthodontic movement: an in silico analysis on stress and displacement.

Abstract

<h4>Purpose</h4>External apical root resorption is an undesirable outcome of orthodontic treatment. Patients with already existing root resorption who require orthodontic treatment should be carefully evaluated. The objective of this study was to evaluate the effect of apical root resorption and different orthodontic forces on stress and displacement in the tooth and periodontium using a three-dimensional (3D) finite element analysis method.<h4>Methods</h4>Two 3D models of an upper central incisor were constructed based on tomographic images. Two models (original tooth length and an apical resorption of 3 mm) and four types of force application (intrusion, extrusion, tipping, and translation) resulted in eight variations from the two original study factors (apical resorption and orthodontic movement). The mechanical properties, mesh, boundary conditions, and loading were added to the specific finite element analysis software (Ansys, Houston, PA, USA). Orthodontic forces (0.6 N) were applied to the brackets to simulate orthodontic movements.<h4>Results</h4>Quantitative analysis showed that the highest von Mises tension values were found in the models subjected to translational movement, regardless of the root condition. The values obtained for the displacement of the studied structures did not differ significantly. In a qualitative analysis comparing teeth with and without apical resorption, teeth with apical resorption showed higher stress concentrations in the cortical bone and periodontal ligament.<h4>Conclusion</h4>Apical resorption did not significantly influence maximum displacement of the involved structures but influenced stress in the periodontal tissues. The translational movement resulted in the highest stress values in the tooth and periodontal tissues.