Evaluation of Stresses on Temporomandibular Joint in the Use of Class II and III Orthodontic Elastics: A Three-Dimensional Finite Element Study

The purpose of the present study was to evaluate the effects of the orthodontic elastic forces used in fixed orthodontic treatment on the temporomandibular joint (TMJ) with normal and anteriorly displaced discs. Four different computer models for Class II and III malocclusion with the TMJ disc in the normal and anterior position were created. All the models were subjected to a constant force of 200g (125 N) on both sides to simulate the elastic pull force placed between the upper and lower jaw with 2 different configurations. Stresses on the TMJ were evaluated using finite element analysis. The stresses in both the condyle and the disc were greater in the Class II models than in the Class III models. Similar results were found between the groups according to the direction of the orthodontic elastics. In the Class II models, the peak value of the maximum principal stresses was located in the posterior region of the condyle in the models with disc in the normal position. The elastic forces used during fixed orthodontic treatment increases the stress on the TMJ, especially for Class II patients. If the disc is in an anterior position, the stresses could be more harmful to the retrodiscal tissue. Thus, during orthodontic treatment, the TMJ should be carefully assessed to avoid irreversible damage.