fibrin and Muscle-Weakness

To evaluate the influence of impaired masseter function during growth on the development of temporomandibular synovitis.. Sixteen 3-week-old male Wistar rats were classified into four groups. The first group served as control; and in the second group, jaw opening was forced for 3 hours when the rats were 9 weeks old. In the third and fourth groups, the masseter muscles were bilaterally resected at 3 weeks of age, and the rats in the fourth group were additionally forced to open their jaw at 9 weeks of age. All rats were sacrificed at 9 weeks. Temporomandibular joint (TMJ) tissue samples were processed for histology, and evaluated for cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expressions by immunohistochemistry to examine the inflammatory changes in the synovial membrane.. The control group showed noninflammatory changes. In the jaw-opening group, vascular dilation and weak COX-2 immunoreactivity were induced by jaw opening in the synovium. In the masseter-resection group, the masseter-resected rats exhibited moderate synovial changes while in the resection with opening group, the masseter-resected rats revealed more significant inflammatory changes including synovial hyperplasia, dilated vasculature, fibrin deposits, and intense immunoreactivity for COX-2 and iNOS, all caused by jaw opening.. These results suggest that masseter activity in the growth period is an important factor in the induction of temporomandibular synovitis.

Topics: Animals; Cyclooxygenase 2; Dilatation, Pathologic; Fibrin; Hyperplasia; Immunohistochemistry; Male; Masseter Muscle; Muscle Weakness; Nitric Oxide Synthase Type II; Range of Motion, Articular; Rats; Rats, Wistar; Stress, Mechanical; Synovial Membrane; Synovitis; Temporomandibular Joint; Temporomandibular Joint Disorders; Vascular Diseases