An exploratory patient-specific finite element study of temporomandibular joint stress distribution following mandibular setback surgery in two distinct clinical scenarios

Mandibular setback surgery is commonly performed to correct skeletal Class III malocclusion, but its effects on temporomandibular joint (TMJ) biomechanics remain unclear, particularly regarding different setback configurations. This pilot study aimed to explore patterns of TMJ stress distribution using two patient-specific finite element models representing distinct clinical scenarios of mandibular setback surgery. Preoperative and six-month postoperative cone-beam computed tomography (CBCT) scans from two female Class III patients undergoing either unilateral (6 mm) or bilateral (3 mm) mandibular setback were used to construct finite element models of the TMJ. Preoperative CBCT scans were obtained in maximum intercuspation before surgery, whereas postoperative CBCT scans were obtained six months after surgery in postoperative maximum intercuspation. Stress distributions in the mandibular condyle, articular disc, and glenoid fossa were analysed under standardised loading conditions. Maximum and minimum principal stresses were evaluated for osseous structures, while von Mises stress was assessed for the articular disc. Both patients exhibited a postoperative reduction in stress magnitudes across TMJ components. Tensile and compressive stresses decreased variably among condyles and fossae, with von Mises stress reductions noted in articular discs, particularly in non-operated sides. Stress concentration regions differed between sides and patients, reflecting anatomical and surgical variability. This patient-specific finite-element study offers preliminary insights into the distribution of stress in the temporomandibular joint (TMJ) following mandibular setback surgery, examined across two distinct clinical scenarios. The results indicate that TMJ biomechanical responses may differ according to individual anatomical characteristics, surgical conditions, and the actual preoperative and postoperative occlusal relationships recorded on CBCT, including posterior open-bite characteristics in the postoperative models. Consequently, the observed stress changes should not be interpreted as representing the isolated biomechanical effects of mandibular setback surgery. Larger studies using validated models are required before broader clinical conclusions can be drawn.