The nature of endochondral ossification in the mandibular condyle of the mouse

Abstract

Abstract Through the application of histological and histochemical techniques, this study demonstrates that the ossification process of the mandibular condyle differs basically from that of other endochondral growth sites. In the epiphyseal plate of a typical long bone, the cartilage cells are known to undergo degenerative processes and death. In the mandibular condyle, however, the cartilage cells keep their vitality throughout the cartilage zones. In the lower border of the calcified cartilage, adjacent hypertrophic cartilage cells fuse after the dissolution of the intervening matrix to form multinuclear chondroclasts. These giant cells reveal marked positive reaction to mitochondrial and lysosomal enzymes. It is suggested that these enzymes are active in the resorption process of the calcified cartilage matrix, which is an integral phase of the ossification mechanism of the condylar growth center. It is believed that the mandibular condyle of the mouse demonstrates a specific type of endochondral ossification, in which the hypertrophic chondrocytes are not dying cells, but contribute actively to the process of bone formation.