Temporomandibular disorders (TMDs) are musculoskeletal conditions affecting the TMJ. Myofascial pain, a common condition associated with TMD, accounts for 45.3% of cases, often involving the masseter muscle, characterized by trigger points and muscle stiffness. Manual palpation assesses muscle hardness but relies on the examiner's skill and experience. The primary objective was to evaluate and compare the stiffness of the masseter muscles using the Muscle Hardness Meter and Ultrasound elastography in patients with TMDs and healthy adult volunteers.

Materials and Methods

This case-control study included 80 patients with myofascial pain and 80 healthy volunteers. Diagnostic criteria for temporomandibular disorders were analyzed in cases within the pain group. A portable muscle hardness meter (Neutones TDM) was used to measure muscle stiffness on both sides. Strain wave elastography was performed using a LOGIQ P9 with a transducer. The thickness and elasticity index of the masseter muscle were evaluated bilaterally.

Results

The study involved 160 patients, with 80 cases and 80 controls, with an average age of 32.9 years. Mean pain was 8.34, mouth opening 30.95 mm, both significantly different from controls (p<0.001). Bruxism was present in 50% of myofascial pain patients, showing a strong link (p<0.001). Muscle hardness and elasticity were higher in cases, with significant differences on both sides, especially in areas with complaints, indicating stiffness. ROC analysis demonstrated high diagnostic accuracy (hardness meter: 0.941, elasticity index: 0.877). Principal component analysis identified three TMD subtypes: (0) high stiffness, pain, limited opening; (1) moderate stiffness, often linked to parafunctions; (2) low stiffness, minimal pain, near-normal functions.

Conclusion

SWE revealed increased stiffness associated with TMD, consistent with global research findings. The muscle hardness meter provides an affordable, non-invasive, chairside tool for assessing muscle stiffness, particularly where elastography isn't available. Principal component analysis grouped patients based on pain and stiffness, aiding in personalized treatment, reducing pain, and improving quality of life.