Journal of Dental Research, Vol 79, 85-89, Copyright © 2000 by International & American Associations for Dental Research Online Journals
Regional differences of metabolism in human masseter muscle by two-dimensional 31P-chemical shift imaging
T. Kanayama, K. Minowa, N. Inoue, T. Yamaguchi, S. Yoshida and T. Kawasaki
Department of Prosthetic Dentistry I, School of Dentistry, Hokkaido University, Sapporo, Japan. kanayama@den.hokudai.ac.jp
Many reports have demonstrated significant region-dependent differences in
the fiber-type composition of the human masseter muscle. Therefore, it is
considered that there is intramuscular heterogeneity of metabolic activity
in the muscle. The present study was carried out, with two-dimensional
Chemical Shift Imaging, to detect differences between the deep and
superficial parts of the human masseter muscle at rest. Masseter muscle
from 11 volunteers, from 20 to 27 years old, was examined, and
characteristic spectra of the inorganic phosphate (Pi), phosphocreatine
(PCr), and alpha-, beta-, and gamma-adenosine triphosphate (ATP) from each
part of the muscles were obtained. In this study, the deep and superficial
parts of the masseter muscle were distinguished by the existence of
aponeurosis. The Pi/PCr, PCr/beta-ATP, and Pi/beta-ATP ratios as well as
the pH in the deep and superficial parts were calculated from the peak
spectra. Compared with the deep part, the Pi/PCr of the superficial part
was lower (p < 0.05) and the PCr/beta-ATP was higher (p < 0.01). The
Pi/beta-ATP and pH showed no significant differences between the two parts.
The results indicate that the superficial part of the masseter muscle
contains more PCr than the deep part, and this may be related to functional
differences between these two parts. In future examinations of the
metabolic activity of the human masseter muscle, the deep and superficial
parts must be measured separately.
