New Aspects of the Histology of the Mandibular Condyle in the Rat

Abstract

The function of the multipotential mesenchymal cells in the mandibular condyle was studied histochemically and histologically in 27 Long Evans/Turku rats. Sagittal sections from the temporomandibular joint were stained with haematoxylin and eosin, toluidine blue, or van Gieson's stain. A weakly orthochromatically stained fibrous layer was followed in the upper region by a weakly metachromatically stained mesenchymal cell layer. Deep within this was a strongly metachromatically stained layer of immature chondroblasts. The metachromasia of the matrix of these layers disappeared abruptly in an anterior direction and gradually in a posterior direction. The changes in the staining reactions are explained by the fact that mesenchymal cells can differentiate into chondrogenic or osteogenic cells depending on the environmental conditions. A new hypothesis is presented according to which regulation of the direction of condylar growth is achieved by choosing the cells for chondrogenesis more posteriorly or anteriorly from among the mesenchymal cells covering the whole condylar cartilage.