title: Variation in masticatory muscle activity during subsequent, submaximal clenching efforts.
abstract: In previous studies to the relative contribution of the jaw closing muscles to the maintenance of submaximal clenching levels, a considerable variation in the electromyography (EMG) activities of these muscles during subsequent efforts was found. In this study, it was examined to what extent this variation could be explained by coincidental variations in mandibular positioning. From seven healthy individuals, a total of 90 EMG sweeps was recorded: three conditions (intercuspal position and two types of stabilization appliances) x three clenching levels (10, 30 and 50% of maximum voluntary contraction level) x 10 repetitions. Mandibular position was monitored with a six degrees of freedom opto-electronic jaw movement recording system. Variations in mandibular positioning during subsequent, submaximal clenching efforts explained up to 25% of the variance in the indices that quantify the relative contribution of the jaw closing muscles to the total clenching effort (P=0.000; ANOVA). Only a weak dependency of positioning upon clenching condition was found whereas during higher clenching levels, the positioning effect tended to be smaller than during lower levels. In conclusion small, coincidental variations in mandibular positioning during subsequent clenching efforts partly explain the variance in EMG activity of jaw closing muscles, especially at lower clenching levels.
authors.affiliation: Department of Oral Function, Section Craniomandibular Disorders, Academic Centre for Dentistry Amsterdam (ACTA), The Netherlands. f.lobbezoo@acta.nl
authors.forename: F
authors.initials: F
authors.lastname: Lobbezoo
authors.forename: J J R
authors.initials: JJ
authors.lastname: Huddleston Slater
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016302:Centric Relation; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000502:physiology; D008406:Masseter Muscle / Q000502:physiology*; D009068:Movement; D009119:Muscle Contraction / Q000502:physiology*; D013703:Temporal Muscle / Q000502:physiology*