Determination of masseter and temporal muscle thickness and reference values of muscle strength by shear wave elastography in HEALTHY adults

The performance of the masticatory system mainly depends on the forces produced by the masseter and temporal muscles. The thickness and stiffness of these muscles is a critical determinant of muscle performance and strength. Therefore, in vivo evaluation of muscle thickness and stiffness can help to understand and improve muscle function. In this thesis study; It was aimed to establish the reference values for the thickness and stiffness of the masseter and temporal muscles at rest and in contraction in healthy adults and to evaluate these values according to age, gender, side and body mass index. In the study, a total of 320 masseter and temporal muscles of 160 (80 female, 80 male) healthy individuals aged between 18-59 were examined by ultrasonography and Shear Wave Elastography. Mean masseter muscle thickness at rest was 1.09±0.21 cm; It was found to be 1.40±0.25 cm in contraction. Temporal muscle thickness at rest was 0.88±0.11 cm; It was found to be 0.98±0.12 cm in contraction. Masseter and temporal muscle thicknesses increased with age at rest and during contraction, but this finding was not significant for temporal muscle. Masseter and temporal muscle thicknesses at rest and during contraction were found to be higher in males than females (p<0.001). While there was a significant difference between the right and left masseter muscle thicknesses at rest and contraction, it was not found in the temporal muscle. Masseter and temporal muscle thickness increased with increasing age and body mass index at rest and in contraction, but these findings were not significant for temporal muscle. Masseter muscle stiffness was evaluated with the transducer in 2 different positions, and these two conditions were compared with each other. Masseter muscle stiffness (ISWE-T) 6.91±1.22 kPa when the transducer masseter muscle was positioned transversely at rest; When the transducer masseter muscle was positioned longitudinally at rest, the stiffness of the masseter muscle (ISWE-L) was found to be 8.49±1.25 kPa. When the transducer masseter muscle is positioned transversely during contraction (KSWE-T) 31.40±7.03 kPa; It was found to be 35.65±7.45 kPa when the transducer masseter muscle was positioned longitudinally during contraction (KSWE-L). Significant differences were found between measurements made with transverse and longitudinal methods, in which masseter muscle stiffness was evaluated both at rest and during contraction. Temporal muscle stiffness at rest 8.84 kPa; It was found to be 20.43 kPa at contraction. Masseter and temporal muscle stiffness at rest and contraction were more common in males than females (p<0.001). There was no significant difference between right and left masseter and temporal muscle stiffness at rest and contraction. Masseter and temporal muscle stiffness decreased with increasing age and body mass index at rest and during contraction, but the decrease in masseter muscle stiffness during contraction was not significant. In conclusion, ultrasonography and SWE can be used as an effective method in the evaluation of chewing muscle thickness and stiffness. Keywords: Masseter muscle, Shear Wave Elastography, Temporal muscle,Ultrasonography.