Objective:The aim of this study was to investigate the features of discs of temporomandibular joints (TMJs), during the joint was in the closing and opening positions.Methods:A total of 9 male university students, 21~23 years old, withoutTMJD symp- tomswere selected for this study, and their bilateral TMJs were examined separately with Siemens 63-SP4000 super conductive MRI system (Germany). The parameters of MRI were 10 cm surface coil, proton-weighted, oblique sagittal section with 3 mm thick. Totally 166 imagineswere obtained including closing and opening positions. Both the area and circle length of the disc sec- tions were measured with the electronic ruler.Results:The disc on the oblique section showed a narrowimagine in the closing po- sition, while a dumbbell-shape in the opening position. The shape of the disc demonstrated larger in the opening position than that in the closing position (P0.05).Conclusion:The shape of the TMJ disc in normal subjects changed a lot in the oblique sagittal section from closing to opening positions, which might be related with the internal pressure changes between these two positions.
