Temporomandibular joint(TMJ) disorders have characteristic clinical findings such as pain, joint sound, and abnormal jaw function. With the rapid progress in TMJ imaging techniques, magnetic resonance imaging(MRI) especially provides the clinician and researcher with the ability to evaluate TMJ disorders(effusion, anterior disk displacement) and the hard and soft tissue of the TMJ. In order to manage the internal derangement of TMJ such as anterior disk displacement, the so-called appliance therapy is commonly used. This technique became the treatment of choice before surgical intervention by many practitioners. The purpose of the present study was to evaluate and determine the efficacy of anterior repositioning splint by means of the change of the position of the disk through pre- and post-treatment MRI. MRI and clinical symptom were carefully recorded in TMJ disorder patients. The relationship between TMJ symptoms such as pain, clicking sound, and disk displacement and effusion in MRI were analyzed. Then, splint therapy was applied for 3 months according to our protocol; at day 1, patients should wear 24 hours, in order to accomodate the splint and then, wearing time is reduced to 12 hours per day for one month. During next 2 months, it is tapered to 8 hours per day according to the evaluation of the clinical symptoms. Post-treatment MRI was obtained after 3 month protocol. This treatment strategy improved the clinical symptoms of TMJ disorder, and effusion and articular disk position showed a significant change. In conclusion, a treatment modality using an anterior repositioning splint therapy is an appropriate method for temporomandibular disorder patients.