Quantitative analysis of masseter muscle hardness with shear-wave elastography

Background: Ultrasound examination is one of the widespread diagnostic imaging methods and still a developing method, which underwent an intense development for biomechanical evaluation of muscles important in temporomandibular disorders, muscle injuries, and training. Aims: This study aims to analyze masseter muscle hardness with shear-wave elastography, especially comparison between during rest and contraction in young adults. Materials and Methods: Thirty-seven volunteers (20 men and 17 women; mean age 25.0 years [age 22–43 years]) were examined by shear-wave elastography with a 14-MHz linear transducer. The shear elastic modulus and thickness of masseter muscles with ultrasonography were compared between during rest and contraction, and between men and women using Mann–Whitney U -test. The statistical analysis of the relationships between contraction and during rest was compared using Wilcoxon signed-rank sum test. P < 0.05 indicates significant differences. Results: Shear elastic modulus data of masseter muscles at contraction were significantly higher than those at during rest ( P < 0.001). The thickness of masseter muscles at contraction was significantly higher than those at during rest ( P < 0.001). Shear elastic modulus data of masseter muscles at during rest were not a significant difference between men and women ( P = 0.402). Similarly, shear elastic modulus data of masseter muscles at contraction were not a significant difference between men and women ( P = 0.223). Conclusions: Shear-wave elastography could be an effective tool for the quantitative analysis of masseter muscle hardness.