title: Antero-posterior activity changes in the superficial masseter muscle after exposure to experimental pain.
abstract: The aim of this randomized, controlled, double-blind study was to examine how the activation pattern of the masseter muscle changes during natural function when experimental pain is induced in a discrete anterior area of the muscle. In 20 subjects, three bipolar surface electrodes and three intramuscular fine-wire electrodes (antero-posterior mapping) were simultaneously attached above and in the right masseter muscle to record the electromyographic (EMG) activity during unilateral chewing before and after infusion of a 0.9% isotonic and 5% hypertonic saline bolus in the anterior area of the muscle. The activity of the contralateral masseter muscle was registered by surface electrodes. In addition, the development of pain intensity was quantitatively measured with a numerical rating scale (NRS). While both saline concentrations caused pain, the hypertonic solution evoked stronger pain. The experiments also provided evidence of a significant although differential activity reduction of the ipsilateral masseter muscle in the antero-posterior direction. The activity reduction decreased with increasing distance from the location of the infusion. The results support the idea that the strategy of differential activation protects the injured muscle while simultaneously maintaining optimal function.
authors.affiliation: Department of Prosthodontics, Dental School, University of Freiburg, Germany. tuerp@zmk2.ukl.uni-freiburg.de
authors.forename: Jens C
authors.initials: JC
authors.lastname: Türp
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Schindler
authors.forename: Maria
authors.initials: M
authors.lastname: Pritsch
authors.forename: Qiguo
authors.initials: Q
authors.lastname: Rong
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004576:Electromyography; D005157:Facial Pain / Q000139:chemically induced* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D006982:Hypertonic Solutions; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D008409:Mastication / Q000502:physiology*; D010147:Pain Measurement; D011897:Random Allocation
chemical_list: D006982:Hypertonic Solutions