Aims: To evaluate the effectiveness of a prefabricated appliance and compare it to the effectiveness of a stabilization appliance in patients with temporomandibular joint (TMJ) pain. Methods: This randomized, controlled multicenter study comprised 48 patients diagnosed with TMJ arthralgia according to the Research Diagnostic Criteria for Temporomandibular Disorders. The effectiveness of a prefabricated appliance (Relax), worn by half of the patients (referred to as the R group), was compared to the effectiveness of a stabilization appliance, worn by the other half of patients (S group). 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. To analyze the differences between groups, the chi-square test and the Mann-Whitney Utest were used, while the Friedman analysis of variance (ANOVA) on ranks was used for the analyses between baseline data and follow-up measurements, all with a significance level set at P < .05. Results: There were no differences between the groups at baseline. A 30% reduction of pain intensity was reported by 62.5% of the R group and 58.3% of the S group at the 10-week follow-up; 58% and 50.3%, respectively, at the 6-month follow-up; and 41.7% in both groups at 12 months. At the 12-month follow-up, pain intensity had decreased and physical function had improved in both groups (P < .005 and P < .016, respectively), without significant group differences. Emotional function (depression and nonspecific physical symptoms) did not change. Overall improvement of "better" to "symptom-free" was observed in 67% of the R group and 58% of 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. Since the prefabricated appliance requires only one visit for construction, it is convenient for both the general practitioner and for the patient.