Associate Professor, Department of Orthodontics, Tehran University of Medical Sciences, Dental Research Center(DRC-TUMS)



Aim: Bent root forms are always a challenging point in an orthodontic treatment. The main aim of this study has been to assess the stress effects of a dilaceration in apical third of an upper central incisor in orthodontic movement.
Materials and Methods: Three FEM models of an upper central incisor were designed with cortical and spongy bone, PDL, and teeth. The only difference between 3D models was the anatomy of the apical fourth of their root. A 30-deg (the first model) and a 60-degree (the second model) dilaceration in the apical fourth of the root were designed in a labial direction. The calculation was in ANSYS Workbench Ver. 11.0. A 1.0 N labio-palatal force was applied in 45 degrees to the horizontal plane in the labial side of the crown. Von mises stress was evaluated along a path of nodes starting at the mid root area at labial moving towards the apex and continuing to reach the mid root lingual region on root surface.
Results: The apical stress did not show a dramatic increase in dilacerated form models starting from 0.11 MPa in normal model to 0.17 MPa in a 60-degree dilacerations model. Moving away from the apex, the stress findings increased which was noticeable between the normal model (0.48 MPa) and the 60-degree model (2.11 MPa).
Conclusion: Based on the findings of this FEN! study, It was shown that the increase in the stress in areas away from the apex can be interpreted as the reason to the start of the external root resorption. There may be other models of the pointed apex root forms to show an increase in the apical area stress which was not the case in this model.