Abstract: Temporomandibular dysfunction (TMD) affects muscles and bones and is frequently associated with the presence of para-functional habits. Frequent signs and symptoms include limited mandibular movements, noise, masticatory and speaking difficulty, headaches, facial and cervical pain, and muscle pain in temporomandibular articulation (TMA). Pain is a common experience, and although it is not always present, the understanding of its physiological mechanisms has grown. The aim of clinical research is to gain knowledge and develop new technologies, including the elaboration of models for evaluation and diagnosis. In the evaluation of muscle function, surface electromyography (EMG) is considered a useful and sensitive tool. Twenty-one volunteers participated in the present study, whose ages ranged from 18 to 30 years. They were divided into 3 groups, the Control (with no dysfunction and with no pain), the TMD (with dysfunction, but no pain) and the PAIN (with dysfunction and with pain), in a manner that followed the sequential steps of the diagnostic protocol. TMD and pain were confirmed using the Research Diagnostic Criteria (RDC) and Fonseca questionnaires, dental examination and anamnesis. Bilateral EMG of the masseter muscles and the anterior portion of the temporal muscles was performed according to the protocol of the EMG Laboratory of FOP-UNICAMP. The signal was captured in three situations and at three times: isometric and isotonic contractions and regular chewing. This way, it was possible to demonstrate the complete absence of joint noise in the control group but its presence in the TMD (33.33% and PAIN (66.66%) groups during protrusion. It was also noted that for all the volunteers there were differences in the answers given at the beginning compared to the end of the RDC, suggesting a certain influence of some questions. During isometry in the control group, there was a functional inversion among the muscles on the right side. In the TMD group, functional inversion was seen also on the right side, along with masseter hyperfunction and a decrease in muscle electrical activity. The PAIN group showed functional inversion, points of muscle failure and a converging profile, indicating muscle fatigue. In isotony, the control group showed uniform masticatory cycles, a wide contraction period and normality period. However, the TMD group showed intensified electrical activity between contractions, while in the PAIN group electrical activity was constant among the muscles, besides the functional inversion among the muscles studied. For the PAIN group, there was notable electrical activity between the contractions and functional inversions. The results of median frequency (means) and RMS (means) in isometry, isotony and regular chewing for the muscles studied were evaluated by statistical analyses. The results do not demonstrate statistically significant differences among the three groups, thereby suggesting that the frequency of motor unit recruitment is similar and that there is no increasing or decreasing… Advisors/Committee Members: UNIVERSIDADE ESTADUAL DE CAMPINAS (CRUESP), Bérzin, Fausto, 1940- (advisor), Universidade Estadual de Campinas. Faculdade de Odontologia de Piracicaba (institution), Programa de Pós-Graduação em Biologia Buco-Dental (nameofprogram), Santos, Lucineia dos (committee member), Sakai, Eduardo (committee member), Pedroni, Cristiane Rodrigues (committee member), Tosello, Darcy de Oliveira (committee member).