Ultrasonographic assessment of segmental masseter muscle thickness and muscle tenderness in individuals with angle class I occlusion and temporomandibular symptoms

OBJECTIVE: To assess bilateral masseter dimensions and palpation tenderness in young adults with Angle Class I occlusion and temporomandibular joint (TMJ) symptoms. METHODS: Forty-nine individuals (37 females, 12 males; aged 20-30 years) underwent clinical assessment of joint sounds, muscle tenderness, mandibular range of motion, deviation/deflection, and associated symptoms. Bilateral ultrasonography measured upper, middle, and lower masseter dimensions at rest and during maximum voluntary clenching. RESULTS: Headache (32.7%), joint sounds (26.5%), and ear pain (8.2%) were reported. Tenderness occurred only in females (right 13.5%; left 10.8%), without significant sex differences. Lower-segment mediolateral thickness differed bilaterally during clenching (p = .049). Segmental thickness changes were significant (p < .05). After multiple-testing correction, GEE showed no significant thickness-tenderness association. CONCLUSION: Masseter dimensions varied by segment and side, with greater thickness changes in lower and middle segments. Ultrasonographic dimensions were not associated with palpation tenderness in this symptomatic cohort.