ABSTRACT
Objective To compare the stress distributions in temporomandibular joint (TMJ) for patients with bilateral anterior disc displacement with reduction (ADDwR) after wearing stabilization splints with two different thicknesses during prolonged clenching by using three-dimensional (3D) finite element methods. Methods The 3D TMJ finite element models were constructed based on CT and MRI image data when the patient was biting in maximum intercuspation (working condition 1), on 3 mm thickness splint (working condition 2) and on 5 mm thickness splint (working condition 3), respectively. The von Mises stresses in the articular cartilages ,the TMJ disc and bilaminar zone under 3 working conditions were evaluated after the maximum jaw-closing forces were applied to the mandible for 60 s. Results The von Mises stress of left TMJ was bigger than that of right TMJ under each working condition. After wearing the 3 mm thickness splint, the disc was not recaptured, the stress was concentrated at the posterior band and bilaminar zone of the disc, and the stress on bilateral TMJ was significantly increased. After wearing the 5 mm thickness splint, the right disc was recaptured, the maximum stress was located at intermediate zone of the disc, and the von Mises stresses of articular cartilages and bilaminar zone were decreased by about 40%. However, the left disc was not recaptured, and the von Mises stresses of glenoid fossa cartilage and bilaminar zone were only slightly decreased by about 6%. Conclusions Different thicknesses of occlusal splints lead to different stresses and stress distribution patterns in TMJ of patients with ADDwR. The 5 mm thickness stabilization splint can reduce the stress of glenoid fossa cartilage and bilaminar zone in ADDwR patients. Disc recapture is helpful for ADDwR patients to relieve TMJ stress. When using stabilization splints for the treatment of ADDwR patients, on the premise of comfort wearing, a thicker splint can achieve more favorable stress distributions.
ABSTRACT
Objective@# To investigate the morphology and position changes of displaced disk with reduction after treatment by modified Twin-block. @*Methods @#19 patients were diagnosed as displaced disk with reduction and they were treated with modified Twin-block from July 2015 to June 2016. 28 temporomandibular joints (TMJ) of these patients were included in the analysis. The disk length, disk-condylar distance, and disk-condylar angle were measured with MRI before and after treatment. Paired t-test was used. Disk morphology before and after treatment was also documented and analyzed by Wilcoxon signed rank test. The statistical significance was set at P<0.01.@*Results @# 28 TMJ disks were anteriorly displaced with reduction. 24 of them were repositioned while the other 4 were still anteriorly positioned after treatment. The disk length was increased significantly (P<0.01) while the disk-condylar distance and disk-condylar angle were decreased significantly after treatment (P<0.01). The disk morphology as hemiconvex (16) and bi planar (9) were the majority before treatment, while biconcave (16) and biplanar (10) were changed to the larger part after treatment. There was improvement on the disk deformation with a statistical significance (P<0.01). Larger disk-condylar distance, disk-condylar angle and severer deformation of disks were observed in the 4 disks without reposition.@*Conclusion @# Modified twin-block is an effective appliance for disk displacement with reduction by repositioning the disk and modifying the disk deformation. However the effect is not good for disks with severer deformation and displacement. Further studies with larger sample and stratified group are still needed.
ABSTRACT
Objective To investigate the clinical value of MRI in treatment choice of anterior disc displacement with reduction. Methods 1.5 T superconducting MR was used to scan bilateral temporomandibular joints in 72 consecutive patients who were diagnosed by MRI as unilateral(66 patients)/bilateral(6 patients) anterior disc displacement with reduction at closed and open mouth. MRI sequences included oblique sagittal T2 weighted image and proton density weighted image, and 78 joints' images were acquired. According to the severity of clinical symptoms, all joints were divided into severe symptom group (45 joints) and mild symptom group (33 joints). Treatment was performed in severe symptom group , while follow up was conducted in mild symptom group. Disk position(angle between posterior margin of the disc and the condyle vertical line), disk morphology(biconcave, biplanar, biconvex, rounded, folded, thick posterior band), and joint effusion (none effusion, mild effusion, moderate effusion, marked effusion) were evaluated by two radiologists. The observer agreement for image evaluation was calculated using Kappa statistics. Group difference in disk position was compared using t-test and Chi-square test was used to compare group difference in disk morphology and joint effusion. Results The Kappa value between two radiologists were 0.816 and 0.832 (P<0.01) on evaluation of disk morphology and joint effusion. Statistical results indicated that the angles between posterior margin of the disc and the condyle vertical line in severe symptom group (54.2 ± 10.9)° were larger than those in mild symptom group (46.4 ± 9.0)° (t=3.37, P<0.05). There was no significant difference in disc deformation incidence between the two groups (χ2=1.18,P=0.277). The common deformation in sever symptom group was thick posterior band (χ2=5.65, P<0.05), and in mild symptom group was biplanar (χ2=5.67, P<0.05). No statistical difference in joint effusion incidence was observed(χ2=1.02,P=0.312). Moderate and marked effusion were more common in sever symptom group than that in mild symptom group (χ2=6.55,P<0.05). Conclusions MRI is a useful tool for making treatment choice in anterior disc displacement with reduction. Treatment should be given when the following occurred on MRI:moderate anterior disc displacement, disc deformation (excepting for biplanar), moderate or marked joint effusion.