Journal of Dental Research, Vol 74, 642-648, Copyright © 1995 by International & American Associations for Dental Research Online Journals
Weakness in mouse masticatory muscles by repetitive contractions with forced lengthening
M. O. Hutchins, H. S. Skjonsby, G. A. Brazeau, U. K. Parikh and R. M. Jenkins
Department of Basic Sciences, University of Texas Health Science Center at Houston Dental Branch 77225, USA.
The etiology of myofascial tenderness and pain of masticatory muscles in
humans is difficult to understand. Parafunctional oral habits such as tooth
grinding or vigorous chewing are thought to be factors. The objective of
this study was to determine if masticatory muscles are susceptible to
weakness and injury induced by repetitive, dynamic, forced-lengthening
contractions. Results would support the hypothesis that contraction-induced
injuries could occur in hyperactive masticatory muscles of humans in
response to parafunctional oral habits. Mice were anesthetized and randomly
assigned to three groups: non-treated controls, treated by repetitive
passive jaw opening, or treated by repetitive isometric tetanic
contractions with lengthening by jaw opening. In each treatment group,
masticatory muscle injury was evaluated by contractile tension, plasma
creatine kinase, and muscle glycogen. Contractile tension was determined at
different stimulation frequencies and was significantly decreased 5 min, 4
h, and 72 h after repetitive contraction/lengthening. Plasma creatine
kinase was significantly elevated at 4 but not at 72 h post-treatment in
mice subjected to repetitive contraction/lengthening. Masticatory muscle
glycogen was not significantly different in any groups at 4 or 72 h
post-treatment. These results indicate that contraction injuries can be
induced in masticatory muscle of mice by forced lengthening contractions
which simulate eccentric contractions.
