OBJECTIVEThe purpose of this study was to investigate the distribution of collagen I, II , X, alkaline phosphatase (ALP) and their roles during initiation of condylar cartilage of the fetal mouse.

METHODSCoronary sections of mandible of mouse embryo aged from 14th to 18th day were studied under light microscope after stained by immunohistochemical method with antibody of types I, II, X collagen and ALP.

RESULTSOn the 14th day of mouse embryo, it was found that mesenchymal cells condensation continuous with the periosteum. Type I collagen and ALP were positive behind the terminal of the ossifying mandibular periosteum where future condylar will form. On the 15th day, positive staining for types I, II collagen was found in mesenchymal cells around hypertrophic cells and type X collagen was detected in hypertrophic cells. ALP was positive in both mesenchymal cells and hypertrophic cells. On the 16th day, type I collagen was observed from periosteal osteogenic cells and mesenchymal cells of the fibrous cell layer to the upper hypertrophic cell layer while Type II collagen was restricted from the lower polymorphic cell layer to the bottom of the hypertropic cell layer. Type X collagen was positive in the hypertrophic cell layer. ALP was positive in periosteal osteogenic cells and hypertrophic chondral cells, but not in the polymorphic cell layer.

CONCLUSIONDevelopment of condylar cartilage is different from that of limb bone. Types I, II, X collagen are expressed in the condylar chondrocyte on the early stage of endochondral ossification. The histology evidence supports the conjecture that condylar cartilage is derived from differentiated mesenchymal cells of the preperiosteum or periosteum of the mandible where ALP is positively expressed.