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Background: The effects of jaw movement pattern on masticatory activity during chewing remains unclear in chronic temporomandibular joint disorders individuals. Objective: to assess the effect of habitual and non-habitual mastication patterns based upon the activation of the masseter and temporalis muscles in individuals with or without temporomandibular joint disorder (TMJD). Methods: Fifty-four participants (age: 18–44 years) were divided into two groups: the TMJD (n=27) and control (n=27) groups. TMJD was identified using the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). Electromyographic activity of the masticatory muscles was measured during 2 tasks: habitual mastication with parafilm (HM) and non-habitual mastication with parafilm (NHM). MATLAB software was used to process electromyography (EMG) signals. The root mean square, symmetry index (SI%), anteroposterior coefficient (APC%) and torque coefficient (TC%) were determined from the processed EMG signal. Results: Reduced right masseter activation was observed for the TMJD group (p<0.05) during jaw agonist phase. During the jaw agonist phase, all muscles presented with more activation during NHM. Symmetry of temporalis (ST%) and APC% were the lowest for HM. TC% was increased for HM. Conclusion: Habitual and non-habitual mastication differ in masticatory activity during jaw agonist and antagonist phase and TMJD individuals presented a different way to recruit muscles under these circumstances. Non-habitual mastication has a more coordinating and stable motor pattern in masticatory activity and has less variability than habitual mastication to assess masticatory activity.

BACKGROUND AND OBJECTIVES:Assessing the possible interactions between the activity of masticatory muscles and quality of life and severity of the temporomandibular disorder can help clarify how changes in muscle activity can be associated with a chronic temporomandibular disorder in women. This study aimed to investigate the correlations between masticatory electrical activity during mandibular resting, maximum voluntary contraction, the severity of the temporomandibular disorder, and quality of life in women with chronic temporomandibular disorder and to compare these parameters with healthy asymptomatic controls. METHODS: Sixty women, 30 with temporomandibular disorder and 30 asymptomatic, participated in this case-control observational study. Diagnostic Criteria for Temporomandibular Disorder was used to identify the presence or absence of temporomandibular disorder. The SF-36 questionnaire was used to assess the quality of life in participants, and ProTMDmulti-part-II was applied to assess the severity of signs and symptoms of temporomandibular disorder. RESULTS: During jaw clenching, the masticatory activity of the right temporal and left masseter muscles, the symmetry of the masseter muscles, and anteroposterior coefficient were significantly smaller in the temporomandibular disorder group than in the asymptomatic group. Masticatory activity at rest, signs and symptoms of chronic temporomandibular disorder, and impairment of the quality of life were correlated using Spearman coefficient (p<0.05). CONCLUSION: Our results contribute to findings on the associations between the masticatory activity in chronic signs and symptoms of the temporomandibular disorder, impairment in quality Correlations between masticatory muscle activity, quality of life, and dysfunction severity in women with chronic temporomandibular disorderRelação entre atividade elétrica mastigatória, qualidade de vida e gravidade da disfunção em mulheres com disfunção temporomandibular crônica