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 shortened regularly to keep them out of occlusion. The controls were fed a hard diet. Immunohistochemical techniques and image analysis were employed to investigate deposition of pro-type I collagen and type II collagen, and the thickness of articular cartilage layers in the mandibular condyle. The immunostaining against pro-type I collagen was most intense 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 but also in the lower hypertrophic layer. The intensity of staining against 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 layers of mature chondroblasts. The total number of chondroblasts recorded was reduced by 35 percent 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 number of chondrocytes are sensitive to alterations in loading.