Effect of Compressive Forces on Extracellular Matrix in Rat Mandibular Condylar Cartilage

To reveal the effect of compressive force on the mandibular condylar cartilage, an appliance was set on 8-week-old Wistar rats to load continuous compressive force. Immunohistochemical and histochemical analyses were performed using toluidine blue, antibodies, and probes for aggrecan, hyaluronan, type II collagen, type X collagen, and 5-bromo-2"-deoxyuridine (BrdU). Histomorphometry and statistical analyses were also performed for aggrecan and BrdU immunostaining. In toluidine blue staining, tissue metachromasia was observed in the transitional zone and the hypertrophic zone of the mandibular condylar cartilage. In histomorphometry and statistical analysis, thickness of the cartilage decreased significantly in all regions in the 3-day experimental group. However, the thickness of the cartilage in the anterior region showed recovery while it decreased continuously in the posterior region. Distributional changes of aggrecan, hyaluronan, type II collagen, and type X collagen in the experimental groups were similar to those for toluidine blue staining. The immunostained area of all these molecules decreased as a result of the decrement of the cartilage area. However, enhanced immunostaining for aggrecan in the proliferative zone was observed only in the 1-day experimental group. BrdU-positive cells, observed in the proliferating zone and the transitional zone, decreased significantly in the experimental group 3 days after force was applied. These results demonstrate that continuous compressive forces on the mandibular condylar cartilage decrease the proliferation of chondrocytes and the amount of extracellular matrices.