Sonographic elastography for assessing changes in masseter muscle elasticity after low-level static contraction

Objectives The purpose of this study was to clarify, by use of sonographic elastography, the changes in elasticity of the masseter muscle after low-level continuous contraction by healthy volunteers. Methods The reproducibility of the elasticity index (EI) was verified by using a scoring phantom for elastography. The EI of the masseter muscle was measured for 10 healthy volunteers before, immediately after, and 10 min after static contraction at 20 % of the maximum force for 10 min. The masseter muscle thicknesses were also measured at these times as a surrogate index of muscle edema. Results The reproducibility of the EI measurements was sufficient for clinical use. The elasticity expressed by the EI increased after low-level contraction compared with that before contraction and changed similarly to the thickness along the time course of the experiment. Conclusions Low-level static contraction increased the elasticity and thickness of the masseter muscle. A potential relationship may exist between elasticity and edematous change in the masseter muscle.