title: Activation time analysis and electromyographic fatigue in patients with temporomandibular disorders during clenching.
abstract: BACKGROUND
  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.
  
  
  CONCLUSIONS
  Results showed motor control strategies during sustained clenching that differentiate controls from TMD patients.
authors.affiliation: Graduate Program in Rehabilitation and Functional Performance, Ribeirão Preto Medical School, University of São Paulo - USP, Brazil.
authors.forename: Natássia Condilo
authors.initials: NC
authors.lastname: Pitta
authors.affiliation: Graduate Program in Rehabilitation and Functional Performance, Ribeirão Preto Medical School, University of São Paulo - USP, Brazil.
authors.forename: Gabriel Silva
authors.initials: GS
authors.lastname: Nitsch
authors.affiliation: Graduate Program in Rehabilitation and Functional Performance, Ribeirão Preto Medical School, University of São Paulo - USP, Brazil.
authors.forename: Mariana Barcellos
authors.initials: MB
authors.lastname: Machado
authors.affiliation: Graduate Program in Rehabilitation and Functional Performance, Ribeirão Preto Medical School, University of São Paulo - USP, Brazil. Electronic address: siriani@fmrp.usp.br.
authors.forename: Anamaria Siriani
authors.initials: AS
authors.lastname: de Oliveira
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008406:Masseter Muscle / Q000502:physiology / Q000503:physiopathology; D018763:Muscle Fatigue / Q000502:physiology; D013703:Temporal Muscle / Q000502:physiology / Q000503:physiopathology*; D013705:Temporomandibular Joint Disorders / Q000175:diagnosis* / Q000503:physiopathology*; D055815:Young Adult
keywords: Electromyography; Fatigue; Masticatory muscles; Temporomandibular joint dysfunction syndrome