Effect of mechanical forces on chondrocyte maturation and differentiation in the mandibular condyle of the rat.

The effects of mechanical factors on the growth of the mandibular condyle were studied by monitoring the maturation of the mesenchymal cells in 55 rats. Thirty-five animals were fed normal pellet food, and 20 were fed a soft diet and their incisors were cut regularly. 3H-thymidine was injected intraperitoneally three days before death at 18, 23, or 33 days. Histologic sections showed the most advanced 3H-thymidine-labeled cells to occur deep in the cartilage, in the lower hypertrophic cell layer in anterior and posterior regions of the condyle, and in the upper hypertrophic cell layer in the superior region at the age of 18 days. A distinct difference in the maturation state of the labeled cells could also be observed between these regions. In animals fed a soft diet, maturation was slower in the superior region of the condyle and faster in the posterior region than in the normal rats. The rate at which cells stepped out of the proliferating cell pool was measured by use of monoclonal antibodies against proliferating cell nuclear antigen. The ratio between labeled cells in the proliferating cell layer and the number of labeled cells beneath it was greater in control animals than in the soft-diet animals. The rate of differentiation and maturation of mesenchymal cells into chondrocytes seems to be controlled by mechanical factors.