Proteoglycan expression in the rat temporomandibular joint in response to a bite-raising appliance

It was hypothesized that a unilateral bite-raising appliance would increase the load applied to the rat temporomandibular joint (TMJ) and thereby induce increased expression of proteoglycans in TMJ articular tissues. To test this hypothesis, six- and nine-week-old, Sprague-Dawley rats received the appliances bonded to their right molars for four weeks. Some nine-week-old rats were housed for an additional four weeks after removal of the appliances they had worn for four weeks. Parasagittal sections of the TMJ disc and mandibular condyle were stained with hematoxylin-eosin. Proliferation of chondroblast-like cells was apparent in the treated specimens. Aggrecan like proteoglycans were detected by safranin O (SO) staining in the condylar cartilage where cell proliferation was evident. A monoclonal antibody (mAb) against versican reacted strongly in the disc and the fibrous layer of the mandibular condyle in the treated groups. Computer quantification of intensities for SO and anti-versican mAb staining revealed that the average intensities of the treated specimens were significantly higher than their corresponding sham-operated controls and the average intensities of the appliance removal specimens showed no significant differences from their corresponding sham operated controls. Thus, the unilateral bite-raising appliance induced an increase in the expression of aggrecan in condylar cartilage and versican in the TMJ disc and the surface fibrous layer of the condyle. The elevated proteoglycan expression may be used as indirect evidence to suggest that the appliance induces an increase in the magnitude of the compressive forces in the rat temporomandibular joint.