Association of Masseter Muscle Shear Modulus and Thickness with Y-Balance Test Performance Among Healthy Adults

The relationship between the stomatognathic system and balance remains poorly understood. This cross-sectional observational study aimed to evaluate associations between ultrasound-assessed masseter muscle shear modulus and thickness and Y-Balance Test performance in healthy adults. Forty-seven individuals were initially recruited, of whom 35 were included in the final analysis (17 women and 18 men; mean age: 22.4 ± 3.3 years). Masseter muscle shear modulus and thickness were assessed bilaterally using ultrasound. Y-Balance Test performance was analysed in the anterior, posteromedial, and posterolateral directions, as well as by composite score and side-to-side asymmetry. For the main analyses based on mean values, Pearson’s correlation showed that higher masseter muscle shear modulus was associated with a lower reach distance in the posterolateral direction (r = −0.495, p = 0.003) and the posteromedial direction (r = −0.414, p = 0.013), and with a lower composite score (r = −0.501, p = 0.002). No statistically significant correlations were found between masseter muscle thickness and Y-Balance Test outcomes. No statistically significant associations remained between masseter muscle shear modulus asymmetry and Y-Balance Test asymmetry after FDR correction. These results suggest a possible association between masseter muscle shear modulus, but not thickness, and Y-Balance Test performance among healthy adults.