The influence of bilateral sagittal split ramus osteotomy on the stress distributions in the temporomandibular joints of the patients with facial asymmetry under symmetric occlusions

Abstract

The aim of this study is to compare the differences in the stress distributions in the temporomandibular joints (TMJs) of the patients with facial asymmetry before and after bilateral sagittal split ramus osteotomy (BSSRO) under the symmetric occlusions using the three-dimensional (3D) finite element method.Ten facial asymmetry patients (Preoperative group, age 24.6 ± 4.8 years) and 10 asymptomatic subjects (Control group, age 26.8 ± 4.9 years) were recruited. After the patients underwent BSSRO, they were further assigned as the Postoperative group. 3D geometries of the finite element models of the mandible, disc, maxilla, and teeth were reconstructed according to cone-beam computed tomography (CBCT) image data. Contact elements were used to simulate the interaction of the disc-condyle, disc-temporal bone, and upper-lower dentition. The muscle forces and boundary conditions corresponding to the central and anterior occlusions were applied on the models of the 3 groups. The finite element models were validated with experimental data showing the accuracy of the simulation results.The simulation predicted preoperative significant differences of stresses between non-deviated sides and deviated sides were disappeared after the surgery under the central and anterior occlusions (P < .05). Almost all stresses in the patient models had significantly decreased after BSSRO, leveling it to the stress values of the normal subjects. Moreover, the simulation results coincided with the clinical cases which showed that BSSRO had helped to release or remove the signs and symptoms of temporomandibular disorders (TMD).In conclusion, BSSRO could correct the asymmetric stress distributions of TMJs and decrease the magnitude of the stresses for the patients with facial asymmetry. Those decreases also associated with the recovery of TMD.

Effect of sagittal split ramus osteotomy on morphologic parameters of temporomandibular joint in patients with mandibular prognathism

“…The magnitudes of SRAL, MJSL, LJSR, and SJS of patients with facial asymmetry were significantly different between the Pre and Post groups. [29,30] Because of the good facial symmetry of MP patients in this study, the effect of SSRO on TMJ morphology parameters of MP patients was not as obvious as that on patients with facial asymmetry. SSRO corrected TMD symptoms of 57% of patients without introducing postoperative symptoms.…”

“…Further research is necessary to answer this question. However, the reduction of joint spaces could lead to squeezing of articular disc in TMJ, [29] which can increase the load on TMJ and lead to osteoarthritis. [30] This in turn may cause pain in the joint and other symptoms of TMD.…”

“…Compared with the previous research, the condylar and ramus angles and joint spaces of facial asymmetry patients were more significantly different from normal people than those of MP patients, [30] which suggested that facial symmetry had a huge influence on the TMJ morphology parameters. In addition, the prevalence of preoperative TMD in facial asymmetry patients (70%) [29] was higher than that in MP patients (29%). Therefore, it could be concluded that TMJ morphology parameters are closely related to the TMD symptoms.…”

“…SSRO corrected TMD symptoms of 57% of patients without introducing postoperative symptoms. [29] The cure rate of TMD of facial symmetry MP patients was 60%, but appeared a patient with postoperative symptoms. Consequently, the therapeutic effect of SSRO might be related to the type of deformity that causes TMD.…”

Biomechanical behaviour of temporomandibular joints during opening and closing of the mouth: A 3D finite element analysis

“…16,17,20 The reference position was near the relaxed position, with less loads both in the TMJ and dentition compared with the ICP. 45 Also, the bilateral condyles were connected by the mandible as they affect each other during oral functions. Unlike previous studies, the bony structures were inhomogeneous and deformable in our study.…”