EFFECT OF REDUCED ARTICULAR FUNCTION ON DEPOSITION OF TYPE-I AND TYPE-II COLLAGENS IN THE MANDIBULAR CONDYLAR CARTILAGE OF THE RAT

A group of rats was fed a soft diet after weaning and the incisors sho rtened regularly to keep them out of occlusion. The controls were fed a hard diet. Immunohistochemical techniques and image analysis were em ployed to investigate deposition of pro-type I collagen and type II co llagen, and the thickness of articular cartilage layers in the mandibu lar condyle. The immunostaining against pro-type I collagen was most i ntense intracellularly in the fibrous and upper chondroblast layers in 30- and 50-day-old rats fed a hard diet. In the rats fed a soft diet, marked intra- and extracellular staining against pro-type I collagen was visible in the upper chondroblast and upper hypertrophic layers bu t also in the lower hypertrophic layer. The intensity of staining agai nst type II collagen was weak in animals on a soft diet, while in the animals fed a hard diet the staining was intense in the superior layer s of mature chondroblasts. The total number of chondroblasts recorded was reduced by 35% at the age of 50 days in the soft-diet compared to the hard-diet animals. The results show that the deposition of type I and II collagens, the thickness of the cartilage cell layers and the n umber of chondrocytes are sensitive to alterations in loading.