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INTRODUCTION: The use of surface electromyography (SEMG) is controversial in the diagnosis and subsequent treatment of temporomandibular disorders (TMD), although there is some evidence that the pattern of the masticatory muscles in TMD patients differs from controls. The aim of this study was to compare relative time of mandibular elevator muscle activation at different levels of activity and median frequency (MF) during sustained clenching. METHODS: Twenty-two women, aged between 18 and 48years, volunteered to participate in the study. The TMD group had 14 participants diagnosed as group Ia muscle disorders (RDC/TMD). The control group had eight healthy individuals. SEMG records were obtained from masseter and temporal muscles during 10s of sustained clenching. Normalized SEMG amplitudes were classified as minimal, moderate and maximal and time of activation in each level of activity was calculated and compared using two-way ANOVA (groups versus time). A slope of the linear regression line that fits MF values over time was calculated as a fatigue index for elevator muscles. RESULTS: Only the temporal muscles of the TMD group showed longer activation time at moderate and minimal activity levels compared to controls. Fatigue indexes were greater for the TMD group compared to controls. CONCLUSION: Results showed motor control strategies during sustained clenching that differentiate controls from TMD patients.

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Objetivo Avaliar a confiabilidade e responsividade do duty factor à dor provinda da desordem temporomandibular Métodos Participaram 20 voluntárias, com média de idade de 29 anos e 6 meses (±9,2), portadoras de desordem temporomandibular miogênica, segundo o critério diagnóstico para pesquisa em Desordem Temporomandibular (RDC/TMD). Foram coletados sinais eletromiográficos nas condições de repouso dos músculos mastigatórios, na presença de dor moderada a severa e na diminuição ou eliminação desta dor após aplicação de Estimulação Elétrica Nervosa Transcutânea durante 45 minutos. Os sinais eletromiográficos de repouso foram processados para obtenção dos valores do tempo de ativação muscular acima de 10% do valor da máxima força de apertamento dentário. A confiabilidade foi testada pelo coeficiente de correlação intraclasse em dados repetidos antes da analgesia. Também foi calculado o erro padrão de medida e mínima mudança detectável. A responsividade da variável foi analisada entre as coletas eletromiográficas realizadas antes e após a analgesia pelo tamanho de efeito e média de resposta padronizada. Resultados Duty factor apresentou valores de coeficiente de correlação intraclasse acima de 0,75 para todos os músculos. O erro padrão foi entre 4% e 8% e a mínima mudança detectável entre 5% e 12%. Na responsividade da variável para a dor, o tamanho de efeito obteve valores entre 0,2 e 0,5 e a média da resposta padronizada, valores acima de 0,8. Conclusão O duty factor apresentou confiabilidade excelente e responsividade à dor da desordem temporomandibular baixa para tamanho de efeito e excelente para média da resposta padronizada. .

Purpose To assess the reliability and responsiveness of the duty factor variable for assessing pain originating from temporomandibular disorders. Methods The sample comprised 20 female volunteers, mean age 29 years 6 months (± 9.2), with a diagnosis of myogenic temporomandibular dysfunction according to the Research Diagnostic Criteria for Temporomandibular Disorders. Electromyographic (EMG) signals were collected at three times: during mandibular rest; in the presence of moderate to severe pain; and when pain was reduced to mild or absent after 45 minutes of transcutaneous electrical nerve stimulation (TENS). Electromyographic signals during mandibular rest were processed to obtain values for muscle activation time greater than 10% of maximum bite force. Reliability was tested with intraclass correlation for repeated data before analgesia. Standard error of measurement (SEM) and minimum detectable change (MDC) were also computed to determine reliability. Responsiveness of duty factor was analyzed between EMG recordings, before and after analgesia, by calculating effect size (ES) and standardized response mean (SRM). Results Duty factor presented intraclass correlation coefficient above 0.75 for all muscles. Standard error of measurement ranged from 4% to 8% and minimum detectable change from 5% to 12%. Regarding the responsiveness of duty factor to pain, effect size values fell between 0.2 and 0.5 and SRM values were greater than 0.8. Conclusion Duty factor showed excellent reliability. However, responsiveness to TMD-related pain was low as expressed by effect size and excellent as expressed by standardized response mean. .

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Objetivo Comparar, entre portadoras de disfunção temporomandibular (DTM) e controles, o tempo de ativação do músculo masseter e do músculo temporal anterior, em diferentes faixas de amplitude eletromiográfica de superfície, durante a mastigação. Métodos Foram avaliadas 22 voluntárias, com idades entre 18 e 48 anos, divididas em Grupo DTM (n=14) do tipo “Ia”, de acordo com o Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TDM) e Grupo Controle (n=8), assintomáticas. Foram registrados, por meio de eletromiografia de superfície, a amplitude e o tempo de ativação dos músculos masseter e temporal anterior, durante mastigação bilateral de Parafilm M® por dez segundos. Os sinais eletromiográficos foram categorizados em três faixas percentuais, 0-39%, 40-74% e 75-100%, relativas ao valor médio de amplitude de três contrações máximas de apertamento dentário. As porcentagens dos tempos totais de ativação (duty factor), em cada uma das faixas de amplitude, foram comparadas entre os grupos pelo teste t-Student, para dados não pareados. Resultados Não houve diferenças significativas do duty factor na comparação entre os grupos controle e DTM. Conclusão A variável eletromiográfica testada não se mostrou útil como ferramenta diagnóstica na prática clínica, o que será possível apenas quando em conjunto com a história clínica e exame físico do indivíduo. .

Purpose This study aimed to compare the time of masseter and anterior temporal muscle activations, in different ranges of surface electromyographic amplitude, between controls and individuals with temporomandibular disorders (TMDs) during mastication. Methods Twenty-two female patients, aged 18-48 years, were divided into the TMD group (n=14; TMD type Ia, according to the Research Diagnostic Criteria for Temporomandibular Disorders) and the control group (n=8; non-diagnosed and asymptomatic individuals). Time and surface electromyography (SEMG) amplitudes from the anterior temporal and masseter muscles were registered during bilateral chewing of Parafilm M® for 10 s. SEMG amplitudes were categorized as 0-39%, 40-74%, and 75-100% of the mean of three maximal clenchings. The percentages of total activation times (duty factor) in each range of SEMG amplitudes were compared between groups using an unpaired Student’s t-test. Results: There were no differences in duty factor comparisons between groups. Conclusion: The activation time of the masticatory muscles was not found to be shorter in the TMD patients than in the controls. Finally, the application of the electromyographic variable proposed in this study may not be considered useful to diagnose type Ia TMD in clinical practice. However, its application may be complementary to the history and physical examination of these patients. .

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