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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 pa⁃ tients 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 docu⁃ mented 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 posi⁃ tioned 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 af⁃ ter treatment. There was improvement on the disk deformation with a statistical significance (P＜0.01). Larger disk⁃con⁃ dylar 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 displace⁃ ment. Further studies with larger sample and stratified group are still needed.