Epidemiological surveys have reported that the prevalence rate for temporomandibular disorders (TMDs) is over 12% of the population. Despite the description of TMDs over 6 decades ago and the prevalence, these conditions remain confusing. This is little agreement as to the features of the diagnoses included in the generic category of TMDs. No therapeutic modalities have proven to be uniformly effective. Recently, an attempt was made to develop a classification system of TMDs based on a set of research diagnostic criteria (RDC). The RDC is comprised of two axes, one based on physical signs and symptoms and one on psychological factors. Although the RDC holds promise, before any diagnostic system is adopted its reliability, validity, and clinical utility need to be established. Only preliminary evidence has been reported supporting the reliability of the physical axis of the RDC. The validity or the clinical utility of the RDC have not been reported. The primary aims of the proposed research are to: (a) validate a classification system comprised of empirically-derived profiles (EDPs) of TMDs based on RDC Axis I, and (b) evaluate the clinical utility of the empirically-derived diagnostic system. Validation the Axis I EDPs requires objective evaluation of bite force and masticatory muscle fatigue, temporomandibular joint (TMJ) sounds, dynamic motion analysis of jaw movements, and jaw imaging. Protocols based on applications from biomedical engineering, kinematics, and electromyography that have been used with other types of chronic pain syndromes have been adapted for this proposal. A critical feature of any diagnostic system is clinical utility. Do subjects in the Axis I EDPs respond to treatments designed to meet the features that describe them? In order to evaluate the utility of the Axis I EDPs, the efficacy of 3 specific treatments will be examined. These treatments (flurbiprofen, EMG biofeedback, and physical exercises) have been customized to match the factors believed to underlie each EDP. To establish the differential utility of the treatments, process measures evaluating the rapidity of response and outcome measures evaluating maintenance of treatment effects will be used.