Inter-arch elastics and corresponding stress on the temporomandibular joint and on the mandibular teeth : a finite element analysis study

Abstract

Introduction: Orthodontic elastics are key auxiliaries used between the maxillary and mandibular arches for occlusal correction and interarch coordination during the treatment of malocclusions. Side effects have been described on neighboring teeth (e.g. altering the occlusal plane) and temporomandibular joints (TMJ; e.g. pain and discomfort). A comprehensive study of the simultaneous effects of interarch elastics on these components was warranted. Aims: 1.Investigate the effects of orthodontic interarch elastics on the TMJ complex and the mandibular teeth under a new scheme of Finite Element Analysis (FEA) that would reflect human individual variation. 2.Compare the different stress generation and displacement potential among and between 3 types of interach elastics: a- Class II elastics applied from maxillary canines to the mandibular 1st molars; b- Class II elastics applied from maxillary canines to the mandibular 2nd molars; and c- Class III elastics from the mandibular canine to the maxillary 1st molar on the TMJ and the mandibular arch. 3.Determine the associations among the responses of TMJ and teeth to the various elastics. Methods: A CBCT scan of an adult female was used to develop a 3D model of the maxilla and mandible (teeth, PDL, condyle, cortical and trabecular bone). The TMJ apparatus included the condylar head, articular disk and temporal fossa. Material properties were designated to each component based on corresponding determinations in earlier cadaver studies (Schwartz-Dabney and Dechow, 2003). The initial model was modified to reflect the variations in thickness and stiffness found in these studies. The obtained reproductions were then subjected to three types of interarch elastics: Class II from the mandibular 1st molars, Class II from the mandibular 2nd molars, and Class III from the mandibular canines. The applied force in each scenario was set at 1N. The resulting Von Mises stresses were recorded at different TMJ levels (condyle, disk, glenoid fossa) and at the mandibular 2nd molars, 1st