INTRODUCTION
In recent years, 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. When muscle fibers are damaged, muscles show shortening and hardening.[1 , 2 , 3 , 4 1 , 2 5 , 6 , 7 , 8
The types of sonoelastography include strain-type sonoelastography and shear-wave sonoelastography.[9 10 , 11 , 12 , 13 , 14 , 15 16 , 17 , 18 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27
MATERIALS AND METHODS
Subjects
This study was approved by the ethics committee of our institution (ECNG-R-400). All volunteers provided written informed consent. 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 at our university hospital from November 2020 to February 2021. The volunteers were our student doctor with healthy and had no missing teeth without wisdom tooth and had no severe medical history or symptoms.
Shear-wave elastography
A conventional ultrasonography examination (grayscale and power Doppler ultrasonography) and shear-wave elastography were performed using a 14-MHz loner transducer (Aplio300, Cannon Medicals Systems, Otawara, Japan) by two oral and maxillofacial radiologists, following our institutional protocol.[28 Figures 1 and 2 ]. The thickness of masseter muscles (mm) using ultrasonography was measured at masseter muscles and maximum diameter at during rest and maximum force contraction, respectively. The volunteer's set position is sitting position on dental unit. The location for measurements is center of vertical length and front-back width. Shear elastic modulus data and thickness were average of measurements three times.
Figure 1: Masseter muscles at during rest with shear-wave elastography
Figure 2: Masseter muscle at contraction with shear-wave elastography
Statistical analysis
The coefficient of determination (R 2 ) from the analyses was calculated to evaluate the relationship between thickness contraction and during rest of masseter muscle. The shear elastic modulus and thickness of masseter muscles were compared between during rest and contraction and between men and women using the Mann–Whitney U -test. The statistical analysis of the relationships between contraction and during rest was compared using the Wilcoxon signed-rank sum test. All analyses were performed with IBM SPSS Statistics Statistical Package version 26 (IBM Japan, Tokyo, Japan). P < 0.05 represented statistical significance.
RESULTS
Table 1 shows the shear elastic modulus data and thickness of masseter muscles at during rest and contraction. Shear elastic modulus data of masseter muscles at contraction (147.6 ± 25.3 kPa) were significantly higher than those at during rest (27.2 ± 12.6 kPa, P < 0.001). The thickness of masseter muscles at contraction (13.1 ± 2.5 mm) was significantly higher than those at during rest (9.9 ± 2.7 mm, P < 0.001).
Table 1: The shear elastic modulus data and thickness of masseter muscles at during rest and contraction
Table 2 shows those at shear elastic modulus data and thickness of masseter muscles at during rest and contraction in men and women. 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). However, the thickness of masseter muscles at during rest of men (11.2 ± 2.6 mm) was significantly higher than those of women (8.4 ± 2.0 mm, P = 0.001). Furthermore, the thickness of masseter muscles at contraction of men (14.5 ± 2.2 mm) was significantly higher than those of women (11.5 ± 1.8 mm, P < 0.001).
Table 2: Shear elastic modulus data and thickness of masseter muscles at during rest and contraction on comparison between men and women in young adults
We plotted during rest (X) against contraction (Y) and observed no significant correlation at shear elastic modulus data (Y = [FIGURE DASH]0.161X + 152.029 [R 2 = 0.007, P = 0.633]; [Figure 3 ]). Similarly, we plotted during rest (X) against contraction (Y) and observed a significant correlation at thickness of masseter muscles (Y = 0.781X + 5.403 [R 2 = 0.687, P < 0.001]; Figure 4 ).
Figure 3: Relationships between contraction and during rest at shear elastic modulus data of masseter muscles
Figure 4: Relationships between contraction and during rest at thickness of masseter muscles
DISCUSSION
Shear-wave sonoelastography is inexpensive, easy to use, noninvasive, takes a short time, and has no adverse effects compared to other prominent methods of medical imaging. This study demonstrated the effectiveness of shear-wave elastography of the masseter muscles.
Ariji et al .[9 P < 0.001). Furthermore, shear elastic modulus data at during rest and contraction were no significant differences between men and women. Arda et al .[29
Hara et al .[30 P = 0.001) and masseter muscle thickness during forceful biting (P = 0.001). In this study, thickness at contraction (13.1 ± 2.5 mm) was significantly higher than during rest (9.9 ± 2.7 mm, P < 0.001). Our study was a significant difference in thickness of masseter muscles depend on sex, but no significant difference in shear elastic modulus data depends on sex. We infer that muscle function influences the thickness of masseter muscles and muscle mass influence shear elastic modulus data.
CONCLUSION
There are several limitations to our study. In future, it will be necessary to increase the number of cases and to examine the relationship masseter muscle thickness, shear-wave sonoelastography maximum bite force, masticatory function, and aging. In conclusion, we analyzed masseter muscle hardness with shear-wave elastography, especially a comparison between during rest and contraction in young adults. The results of the present study indicate that shear-wave elastography could be an effective tool for the quantitative analysis of masseter muscle hardness.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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