Objectives: To study the effectiveness of a prefabricated appliance (Relax™), referred to as the R-group, compared to a stabilization appliance (S-group) in patients with temporomandibular joint (TMJ) pain, when used during sleep. Methods: This randomized, controlled multicenter study comprised forty-eight patients diagnosed with TMJ arthralgia according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). Treatment outcome was assessed according to the recommendations by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) on an intent-to-treat basis. Results: There were no differences between groups at baseline. A 30 % reduction of pain intensity was reported by 63 % in the R-group and 58 % in the S-group at the 10-weeks follow-up, and 42 % in both groups at 12months. At the 12-month follow-up, pain intensity had decreased and physical function improved in both groups (Ps < 0.005 and Ps < 0.016, respectively), without significant group differences. Emotional function (depression and non-specific physical symptoms) did not change. Overall improvement “better” to “symptom-free” was observed in 67% in the R-group and 58% in the S-group. No side effects occurred. Conclusion: The effectiveness of the prefabricated appliance seems to be similar to that of the stabilization appliance in alleviating TMJ pain. The prefabricated appliance is handy for the general practitioner and convenient for the patient and can be recommended for the treatment of patients suffering from TMJ pain, when used only during sleep.