Experimental model of temporomandibular joint arthritis: Evaluation of contralateral joint and masticatory muscles

Objective: To investigate morphological and biochemical changes in an experimental model of temporomandibular joint (TMJ) arthritis, as well as examine contralateral joint involvement and morphometric aspects of masticatory muscles in affected animals. Design: Forty Wistar rats were allocated into three groups, as follows: a healthy control group (HG); and a group with arthritis induced in the left TMJ (IG); and a contralateral group with noninflamed right TMJ (CG). Arthritis was induced by intra-articular injection of 50 mu L of Complete Freund's Adjuvant (CFA). Morphological analysis was performed using histological sections of TMJs stained with hematoxylin-eosin, picrosirius and toluidine blue. In addition, histomorphometric analyses of the articular cartilage, articular disc and masticatory muscles, were performed. Biochemical analysis of TMJ tissues included dosage of sulfated glycosaminoglycans (GAGs), zymography of the Matrix Metalloproteinases (MMPs) 2 and 9 and ELISA for the cytokines IL-6, TNF-alpha and IL-1 beta. The data were analyzed by paired and unpaired t-tests, with a p < 0.05. Results: IG animals presented morphological and biochemical changes in their TMJ, including synovial membrane hyperplasia; chronic inflammatory infiltrate; collagen fiber disorganization in the disc; reduced proteoglycans in the cartilage; greater disc thickness; lower cartilage thickness; lower feed intake; higher activity of MMP-9 and MMP-2, and higher concentration of IL-6, TNF-alpha, and IL-1 beta, as compared to HG. CG animals showed posterior disc thickening; reduced proteoglycans in the cartilage; lower collagen fiber organization of the disc; active MMP-9, and higher concentration of IL-6 and TNF-alpha compared to HG animals. Articular inflammation reduced the area and diameter of fibers of the temporal (right), medial pterygoid (left), and lateral pterygoid (right and left) muscles as compared to HG animals. Conclusion: TMJ arthritis reduced the area and diameter of masticatory muscle fibers and caused morphological and molecular changes in the contralateral joint.