Investigation of stress distribution in temporomandibular joint in symmetric and asymmetric mandibular setback cases in patients with class III dentofacial deformity using finite element analysis method

Aim: The aim of this study was to investigate the stress distributions on the mandibular condyle, articular disc and glenoid fossa as a result of the changing jaw-condyle position with bilateral sagittal split ramus osteotomy (BSSRO) after symmetric and asymmetric mandibular recession procedures in patients with class III dentofacial deformity with and without facial asymmetry and to evaluate the effects of orthognathic surgery on these anatomical structures by three-dimensional finite element analysis (FEA) method. Materials and Methods: Our study was conducted with 2 patients who underwent orthognathic surgery. The patients included in our study were divided into 2 groups according to surgical planning. The first group (Group 1) consists of patients who underwent asymmetric mandibular recession; the second group (Group 2) consists of patients who underwent symmetric mandibular recession. CBCT images of the patients were obtained before surgery and at 6 months after orthognathic surgery. These CBCT images were modeled in a computer environment using the finite element analysis method (FEA). Anatomical sections colored according to the force scale were obtained from the obtained models in order to better evaluate the stresses on the temporomandibular joint structures. The distribution of stresses on the temporomandibular joint structures and the effects of orthognathic surgery on the stress and force distributions on these anatomical structures were analyzed through the models. In our study, anatomical landmarks of TMJ were evaluated separately in both groups (Group 1 and 2) on the right and left sides (bilateral) before and after the operation. The evaluated parameters include maximum principle stress (highest tension), von misses stress and minimum principle stress (highest compression) values. Results: In both groups in our study, postoperative stresses decreased compared to preoperative stresses. This situation is observed in all stress types. The highest stress change is observed in the von misses stresses on the non-recession side articular disc of Group 1 with 55.9%. The lowest stress change is observed in the tensile stresses on the mandibular condyle of the non-recession side of Group 1 with 2%. This is followed by the tensile stresses on the glenoid fossa of the non-recession side of the same group with a value of 5.9%. Except for one stress group, it was observed that the postoperative locations of all stresses in the other groups did not change compared to their preoperative locations. It was analyzed that the tension type stresses in the mandibular condyle and glenoid fossa were located anteriorly to these structures, while the compression type stresses were located posteriorly. It was observed that the von misses stresses observed in the articular discs were concentrated in the anterior parts of the discs. The only stress group that changed its position by shifting laterally after the operation was the highest tensile stresses on the glenoid fossa of Group 1, which was not recessed. Conclusion: In conclusion, the stresses on the main structures forming the temporomandibular joint, such as the mandibular condyle, articular disc and glenoid fossa, decreased after asymmetric and symmetric mandibular recession surgeries using the BSSRO technique. It is thought that orthognathic surgery can reduce temporomandibular joint problems by alleviating high intra-articular stress levels caused by mandibular asymmetry and prognathism. The most important limiting factor of this study is the small sample group due to the cost of the finite element analysis method. The number of patients and models should be increased to reach more detailed results on the subject. Keywords: Orthognathic Surgery, Temporomandibular Joint, Mandibular Setback, Finite Element Analysis