title: Experimentally induced masseter-pain changes masseter but not sternocleidomastoid muscle-related activity during mastication.
abstract: The aim of this study was to verify the effects of induced masseter-muscle pain on the amplitude of muscle activation, symmetry and coactivation of jaw- and neck-muscles during mastication. Twenty-eight male volunteers, mean age±SD 20.6±2.0years, participated in this study. Surface electromyography of the masseter and sternocleidomastoid (SCM) muscles was performed bilaterally during mastication of a gummy candy before and after injections of monosodium glutamate solution and isotonic saline solution. As a result, we observed a decrease in the amplitude of activation of the masseter muscle on the working side (p=0.009; d=0.34) and a reduction in the asymmetry between the working and the balancing side during mastication (p=0.007; d=0.38). No changes were observed either on the craniocervical electromyographic variables. In conclusion, experimentally induced pain reduced the masseter muscle activation on the working side, thereby reducing the physiological masseters' recruitment asymmetry between the two sides during mastication. No effects on SCM activity were detected. These results may partly explain the initial maladaptative changes underlying TMD conditions.
authors.affiliation: Graduate Program of Human Communication Diseases, Federal University of Santa Maria, Santa Maria, RS, Brazil. Electronic address: fepasinato@gmail.com.
authors.forename: Fernanda
authors.initials: F
authors.lastname: Pasinato
authors.affiliation: Graduate Program in Health Science and Technology, University of Brasília, Brasília, DF, Brazil.
authors.forename: Clarissa C
authors.initials: CC
authors.lastname: Santos-Couto-Paz
authors.affiliation: Graduate Program in Health Science and Technology, University of Brasília, Brasília, DF, Brazil.
authors.forename: Jorge Luis Lopes
authors.initials: JL
authors.lastname: Zeredo
authors.affiliation: Department of Dentistry, Faculty of Health Sciences, University of Brasília, DF, Brazil.
authors.forename: Sergio Bruzadelli
authors.initials: SB
authors.lastname: Macedo
authors.affiliation: Graduate Program of Human Communication Diseases, Federal University of Santa Maria, Santa Maria, RS, Brazil; Department of Physical Therapy, Federal University of Santa Maria, Santa Maria, RS, Brazil.
authors.forename: Eliane C R
authors.initials: EC
authors.lastname: Corrêa
mesh_terms: D018698:Glutamic Acid / Q000008:administration & dosage / Q000633:toxicity; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D008409:Mastication; D009119:Muscle Contraction; D063806:Myalgia / Q000209:etiology / Q000503:physiopathology*; D009334:Neck Muscles / Q000503:physiopathology*; D055815:Young Adult
chemical_list: D018698:Glutamic Acid
keywords: Experimental jaw-muscle pain; Mastication; Masticatory muscles; Neck muscles; Surface electromyography