• M K A van Selms, K Wang, F Lobbezoo, P Svensson, L Arendt-Nielsen, and M Naeije.
• Department of Oral Function, Academic Centre for Dentistry Amsterdam, Louwesweg 1, 1066 EA Amsterdam, The Netherlands.
• Clin Neurophysiol. 2005 Jun 1; 116 (6): 1415-23.

ObjectiveTo examine the effects of experimentally evoked masticatory muscle fatigue, without and with experimental muscle pain, on the short-latency jaw-stretch reflex, using a randomised crossover design.MethodsReflexes were evoked in both the masseter and temporalis muscles in 15 men and 13 women. The study was performed in two blocks, both containing 3 experimental conditions (before, directly after, and 15 min after provocation). Provocation consisted of a fatiguing chewing test, followed by an intramuscular injection of either isotonic saline (IS; non-painful) or hypertonic saline (HS; painful).ResultsNo significant effects of the experimental condition 'fatigue+IS' were found for any of the reflex outcome variables. For each muscle, the 'fatigue+HS' condition yielded significantly higher normalized reflex amplitudes than the other conditions. Several muscles displayed gender differences regarding both onset latency and normalized reflex amplitude.ConclusionsExperimentally evoked mild-to-moderate muscle fatigue does not modulate the human jaw-stretch reflex. On the other hand, experimental muscle pain, evoked after the performance of a fatiguing chewing test, does yield a facilitation of this reflex. The gender differences found in both onset latency and peak-to-peak amplitude stress the need to take gender into consideration in future jaw reflex studies.SignificanceThe sensitivity of the human jaw-stretch reflex can be modulated by HS-induced muscle pain; not by muscle fatigue that is provoked by intense chewing.

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