Publications

Myoton Clarification Note: A Guide to Interpreting the Inverse Relationship Between Logarithmic Decrement and Tissue Elasticity

Background: Bruxism is a complex condition with a multidimensional aetiology, wherein it is cross-sectionally associated with dysfunction of the autonomic nervous system (ANS); however, the relationships among ANS activity, muscle biomechanics, and pain remain unclear.

Objective: This study examined links among ANS activity, masticatory biomechanics, and pain in clinically based bruxism using quantitative methods.

Methods: This observational case-control study included 44 individuals with clinically based bruxism and 45 controls. Pain intensity (at rest and during chewing via Numeric Pain Scale), ANS activity (heart rate variability, heart rate, and respiratory rate via Polar H10), and masticatory muscle properties (tone, stiffness, and elasticity via MyotonPRO) were measured.

Results: Compared to controls, the bruxism group showed impaired sympathovagal balance (LF/HF ratio: p < .001), reduced parasympathetic activity (HF power: p = .014), and altered muscle biomechanics (increased tone and stiffness, decreased elasticity; all p < .001). Correlation analyses found that lower HF power was negatively correlated with masseter stiffness (r = –.373, p = .043) and pain intensity (rest: r = –.387, p = .039; chewing: r = –.572, p = .018). Increased muscle tone and stiffness were positively correlated with pain intensity (p < .05).

Conclusion: This exploratory study suggests a significant relationship among ANS dysfunction (specifically reduced parasympathetic activity), impaired muscle biomechanics, and pain in clinically based bruxism. These findings may provide a conceptual basis for multidisciplinary treatment strategies targeting ANS regulation in bruxism management.

Keywords: bruxism, autonomic nervous system, masseter, tone, stiffness

This exploratory study suggests that individuals with clinically based bruxism may present with a complex profile characterised by autonomic imbalance and changes in the biomechanical properties of the masticatory muscles. Our research indicates that diminished vagal tone is significantly associated with increased masseter muscle stiffness and pain intensity in bruxism. These results may support the presence of an interaction between the ANS and the musculoskeletal system in individuals with clinically based bruxism. From a clinical perspective, these results emphasise the importance of incorporating holistic, multidisciplinary approaches that target autonomic regulation into treatment strategies for bruxism management, alongside traditional methods.