Effects on loads in temporomandibular joints for patients with mandibular asymmetry before and after orthognathic surgeries under the unilateral molar clenching

Orthognathic surgery is a useful treatment for the correction of mandibular deformity. Different from other occlusions, unilateral occlusion is frequently used in mastication and influences functions of temporomandibular joints (TMJs). However, stress distributions in TMJ before and after orthognathic surgeries are not under consideration in treatments, crucial to pre- and postoperative temporomandibular disorders (TMDs). The study aims to analyze stress distributions in TMJs for patients with mandibular asymmetry before and after orthognathic surgeries under the unilateral molar clenching. Ten asymptomatic subjects (control group) and 10 patients with mandibular asymmetry were recruited for the study. All patients underwent orthognathic surgeries and were grouped as preoperative and postoperative for the purpose of comparing stress variation in TMJ before and after surgery. Finite element models corresponding to the unilateral molar clenching were constructed. The contact stresses at the ipsilateral side for asymptomatic subjects were significantly greater than those at the contralateral side, while the third principal stresses at the contralateral side were significantly greater than those at the ipsilateral side. No significant difference of stress distribution in TMJ between two sides appeared for the preoperative group. After surgeries, the stress distributions were close to the normal states. The stress of the preoperative group was found to be significantly higher than those of the control and postoperative groups. The variations in stresses before and after the surgery were consistent with the signs and symptoms or recoveries of TMD. Orthognathic surgery could alleviate the high level of stresses caused by mandibular asymmetry and is helpful for the recovery of TMD.