Light microscopic and ultrastructural observations of the calcifying zone of the mandibular condyle in the rat.

The hypertrophic stage of development of the rat mandibular condyle was investigated in 16 and 26-day-old rats by electron microscopy. Interest was focused on the zone of mineralization and erosion. It was observed that capillaries invaded the lower level of the hypertrophic zone, without any previous chondroclastic resorption of calcified partitions. The partitions surrounding the hypertrophic chondrocytes were not mineralized around their entire circumference at the level of capillary penetration. The capillaries were accompanied by perivascular cells but these showed no similarities to chondroclasts. Multinucleated chondro- or osteoclasts were however present at a lower level of the subchondral area. It is suggested that there are no inherent differences with respect to the pattern of mineralization and erosion between the epiphyseal growth plate and the developing mandibular condyle.