Ultrasonographic assessment of the effects of unilateral mastication on the temporal and masseter muscles.

Statement of problem: Unilateral mastication is a complex problem affecting the masticatory muscles. Quantitative evaluation of the contraction efficiency of the muscles to determine what effect unilateral mastication has on them is lacking.

Purpose: The purpose of this clinical study was to investigate the differences in masseter and anterior temporal muscle thickness and elastography values between the masticatory and nonmasticatory sides in patients with unilateral mastication habits using ultrasonographic evaluation.

Material and methods: Twenty-five individuals with unilateral mastication habits were included in the study. The anterior temporal and masseter muscles of the participants were evaluated using ultrasonography at rest and during maximal voluntary contraction. Muscle thickness measurements were performed in the transverse plane, and shear wave elastography values were recorded in kilopascals. Differences between the 2 groups were determined by analyzing the obtained data with the paired samples t test (α=.05).

Results: The mean thicknesses of the masseter muscle on the masticatory side at rest and during maximal contraction were 12.2 ±1.9 mm and 14.6 ±2.0 mm, respectively, whereas on the nonmasticatory side, these values were 11.3 ±2.0 mm and 13.6 ±2.2 mm (P<.05). Similarly, the thicknesses of the anterior temporal muscle at rest and during maximum voluntary contraction also showed significant differences between the masticatory and nonmasticatory sides (P<.05). Elastography measurements revealed significantly higher elasticity values on the masticatory side.

Conclusions: In individuals with unilateral mastication, both the masseter and anterior temporal muscles on the masticatory side had significantly higher thickness and elastography values. These ultrasonographic evaluations can help understand the adaptive mechanisms of the masticatory muscles.