Ultrasound Findings of the Masseter Muscle in Patients with Bruxism

Background: Bruxism is a common parafunctional activity that causes destructive effects on the teeth, periodontal tissue, and temporomandibular joint, leading to hypertrophy and myositis of the masseter muscle. This study aimed to evaluate the sonography findings of masseter muscle among women with bruxism and compare them with those among healthy females. Methods: The statistical population of this study consisted of 45 female volunteers, including 23 patients with bruxism and 22 healthy subjects, referring to the Prosthodontics Department. Masseter muscles were evaluated by sonography in each group bilaterally, at rest and maximum contraction positions, and in longitudinal and transverse planes in terms of thickness. It was also examined in terms of the pattern (type I, II, and III), echogenicity (hypo, intermediate, and hyper), internal structure (homogeneous and heterogeneous), and muscle fiber limits (well-defined, poorly-defined, and ill-defined). Results: In the study of three variables of echogenicity, internal structure, and boundaries of muscle in patients with bruxism, less echogenicity (P≤0.011), heterogeneous structure (P≤0.003), and indeterminate boundaries (P=0.000) were predominant, and there was a significant relationship between the two groups. Moreover, the examination of the difference in muscle thickness between the two groups showed that only the thickness of the left masseter muscle in the longitudinal plane and at rest position was significant between the healthy and bruxism groups (P=0.040). Conclusion: There were marked sonographic changes in the masseter muscle in women with bruxism, indicating that the bruxism may affect the masseter muscle.