Assessment of Variations of Pressure Sensitivity Within and Between Chronic Painful Jaw Muscles—A Case–Control Clinical Study

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Abstract
Background: Orofacial myofascial pain shows variable muscle sensitivity, referred pain, and complex spatiotemporal pressure processing profiles. Methods: This participant‐, examiner‐ and data analyst‐blinded case–control study compared masticatory muscle sensitivity and entropy patterns between 28 chronic myofascial TMD pain patients and 28 age‐ and sex‐matched controls, introducing a comprehensive approach for ‘topoalgesia’ assessment. Mechanical pain sensitivity (MPS) was assessed at nine sites on the masseter and temporalis muscles bilaterally using a palpometer with 0.5, 1.0 and 2.0 kgf for 2 s. Participants rated MPS on a 0–50–100 numeric rating scale after each palpation and reported referred sensations. Entropy and center of gravity (COG) were analysed. Results: Chronic myofascial TMD pain patients reported significantly greater MPS scores than controls across all force levels and muscles ( p < 0.05). Both groups showed increased MPS with higher applied forces. TMD patients exhibited significantly greater entropy in the masseter muscle at 0.5 and 1.0 kgf, and in the temporalis muscle at 2.0 kgf ( p < 0.001). TMD patients also reported more referred sensations than controls across all force levels ( p < 0.001). COG analysis showed myofascial TMD patients presented more centrally located COG within the masseter muscle than controls particularly at lower forces. Conclusions: Results suggest that chronic myofascial TMD patients present greater muscle sensitivity, differing entropy profiles across muscles and force levels, and distinct spatiotemporal patterns compared to controls, associated with more frequent referred sensations. These findings contribute to understanding chronic muscle pain manifestations, and topoalgesia may help better track disease progression or remission over time. Significance Statement: Quantification of spatial variation in pressure sensitivity (topoalgesia) showed that chronic myofascial TMD patients diverge from healthy controls at 0.5 kg and 2.0 kg palpation forces, but not at 1.0 kg, identifying force‐specific parameters that could sharpen diagnostic sensitivity for orofacial pain.

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