Proteoglycan expression in the rat temporomandibular joint in response to unilateral bite raise

The vertebrate articular tissue consists of collagen fibers embedded in a ground substance. Collagen resists tensile forces, while proteoglycans in the ground substance provide resilience and resistance to compression. It was hypothesized that unilateral bite raise would induce increasing expression of proteoglycans in TMJ articular tissues. As a test of this hypothesis, six- and nine-week-old Sprague-Dawley rats received unilateral bite-raising appliances bonded to their right upper molars for 4 wks. A group of nine-week-old rats was housed for an additional 4 wks after removal of the appliances they had worn for 4 wks. Proteoglycans that carry abundant chondroitin sulfate and keratan sulfate side-chains, most likely aggrecans, were detected by safranin O in the fibrocartilaginous zone of the condyle in parasagittal sections. A monoclonal antibody against a large chondroitin sulfate proteoglycan related to versican reacted strongly in the surface fibrous layer of the mandibular condyle and moderately in the discs of the treated specimens. Computer quantification for safranin O and anti-versican antibody staining revealed that the average intensities of the treated specimens were significantly higher than those of their corresponding sham-operated controls, and the average intensities of the treatment-reversal specimens had no significant differences from their corresponding sham-operated controls. Thus, unilateral bite raise appeared to have induced an increase in the expression of aggrecan in the condylar cartilage and a proteoglycan related to versican in the TMJ disc and the articular surface of the condyle. The elevated proteoglycan expression is interpreted to suggest that unilateral bite raise leads to an increase in the magnitude of compressive forces in the rat temporomandibular joint.