Abstract: PURPOSE: This study was aimed to evaluate the changes of temporomandibular joint (TMJ) space after treatment of disc displacement with reduction (DDWR) for Class Ⅱ malocclusions. METHODS: Disc repositioning was obtained with functional appliance for 42 adolescent patients diagnosed as unilateral DDWR. MRI scans were used before treatment (T1), at the start of treatment (T2) and after functional treatment (T3). Comparing with the normal joint, the change of joint space index (JSI) was calculated between T1 and T3. The anterior, posterior, and superior joint spaces were analyzed on the largest sagittal plane among T1, T2 and T3. Student's t test was performed using SPSS 16.0 software package for data analysis. RESULTS: The average treatment duration was 9 months. Short duration was seen in younger patients. During the phase of T1, the value of JSI of DDWR was significantly higher than that of the control (P<0.05). This indicated the anterior space was larger than the posterior space for DDWR. There was a decrease in the anterior space (P<0.01) and an increase in the post-superior space at T2 (P<0.01). A significant increase in the anterior space (P=0.01) and a remarkable reduction in the post-superior space (P<0.01) were observed at T3 compared with T2. There was a significant increase in the post-superior space and no significant decrease in the anterior space at T3 compared with T1 for DDWR. CONCLUSIONS: This study indicates that the TMJ space is well-distributed after functional treatment and disc repositioning for DDWR. Supported by Research Fund for Young College and University Teachers of Shanghai Municipal Education Commission (jdy11027), Research Fund of Shanghai Municipal Health Bureau (20134Y061) and Scientific Research Fund of Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine (2012-12).

Key words: Disc displacement with reduction, Functional appliance, Disk repositioning, MRI, Temporomandibular joint space