Evaluation of the effect of different condyle neck angles on the stresses in the temporomandibular joint in orthognathic surgeries with counterclockwise rotation of the upper jaw by finite element analysis

The aim of this study is to determine the effects of different condyle neck morphologies on the stresses in the temporomandibular joint in patients with class 2 skeletal deformity with a large occlusal plane angle treated with different amounts of maxillary impaction which the maxillomandibular complex is rotated counterclockwise. In our study, a total of 9 models were obtained to evaluate three different amounts of maxillary impaction (2 mm, 4 mm, 6 mm) and 3 different condyle morphologies (anterior angled, perpendicular, posterior angled). In order to simulate different amounts of maxillary impaction, jaw models were obtained with virtual planning software with DICOM data of a patient who has class 2 skeletal deformity and high occlusal plane angle. Standard Le fort I and BSSO osteotomies were simulated, and 2 mm, 4 mm and 6 mm impactions in the maxilla of the patient were simulated, respectively. Afterward, mandible models moved according to the target occlusion, the condylar segments were rotated in such a way that the lower border of the mandible was aligned, and the rotations that would occur due to the maxillary impactions were transferred to the condylar segment models. After the bite forces were simulated from the posterior region, the stress values in the condyle, disc and glenoid fossa were evaluated. The mean von Mises stress values were found to be higher in the model with posterior angled condyle and 6 mm maxillary impaction models than in the other models. The lowest von Misses stress values were observed in the models with vertical condyle morphology and 2 mm maxillary impaction. In orthognathic surgical procedures with counterclockwise rotation, as the amount of maxillary impaction increases, the amount of stress on the condyle increases. All Von Mises stress values were found to be higher in posterior angled condyle models compared to anterior angled and vertical condyle models. It should be kept in mind that in Class 2 patients with a high occlusal plane angle, stresses in the joint and surrounding tissues and related complications such as condylar resorption may be encountered more frequently with the increased amount of counterclockwise rotation and posteriorly angled condyle morphology. In these kinds of clinical situations different treatment procedures decreasing the condylar rotation should be considered.