title: Relaxation rate in the assessment of masseter muscle fatigue.
abstract: The aim of this study was to assess a simple method of measuring relaxation rate in the jaw-closing system for the purpose of quantifying jaw muscle fatigue. A summary of the various different methods of measuring relaxation rate is also provided. The rates of twitch contraction and relaxation were measured in 30 symptom-free subjects following bilateral direct electrical stimulation of the masseter muscles. The resulting twitch force was recorded via a force transducer placed between the anterior teeth. The transducer was held between the teeth with as little force as possible while four single stimuli were delivered at 5-s intervals. The stimulating electrodes were then removed and replaced and the experiment was repeated. The force records of the resulting twitches were averaged and the half-contraction time, twitch amplitude and half-relaxation time were measured. There was a significant difference in half-relaxation time between males and females, being faster in females (P=0.0045, independent t-test). No significant difference was found in twitch amplitude and half-contraction time between males and females. Half-relaxation time and half-contraction time were independent of twitch amplitude. This method of measuring the relaxation rate of the masseter muscles was found to be practical and the results were reproducible between sessions.
authors: University of Glasgow Dental School, Glasgow, UK. m.f.lyons@dental.gla.ac.uk
authors: M F
authors: MF
authors: Lyons
authors: A
authors: A
authors: Aggarwal
mesh_terms: D000328:Adult; D001732:Bite Force; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012044:Regression Analysis; D015203:Reproducibility of Results; D012737:Sex Factors; D012815:Signal Processing, Computer-Assisted; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013997:Time Factors; D014159:Transducers; D014743:Videotape Recording