Distribution and characterization of proliferative cells in the rat mandibular condyle during growth

Distribution of proliferative cells and localization of types I and II collagen were examined in the rat mandibular condylar cartilage of 36 long-Evans/Turku strain rats during normal postnatal growth using an immunohistochemical method combined with histomorphometry. There were considerable differences in the thickness of the proliferative cell layer in the condylar head, with most mitoses occurring in the postero-superior area. It was found that the extracellular matrix of the proliferative cells does not stain for type II collagen in 20-day-old and older rats, and that besides the subchondral bone, the strongest intensity for type I collagen stain was always localized in the articular surface of the condylar head. Statistically significant overlapping of the proliferative cell layer and the one secreting type II collagen occurred during the earlier stages of development, particularly in the postero-superior area of the condylar head. As type II collagen is considered to be a marker for identification of typical cartilage cells, the findings indicate that, in addition to undifferentiated cells, a portion of the proliferative cells can be characterized as chondroblasts during the early postnatal period in rats, but not in the later stages of development. The developmental phase of the condylar cartilage should therefore be taken into consideration when the effect of various biomechanical and humoral/hormonal factors on growth of the condylar cartilage is examined.