• Applied Microscopy
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• v.31 no.3
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• pp.287-305
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• 2001

To investigate a role of cartilage canals in osteogenesis and growth of the vertebrae, in human fetuses ranging from 50 mm to 260 mm crown rump length were studied by electron microscopy. The initial appearance of cartilage canals of the vertebral body was observed at 60 mm fetus. In 80 mm fetus, primary ossification center in the vertebral body was first noted. The vertebral body showed calcified chondrocytes surrounded by a tone of hypertrophied chondrocytes and deep canals which terminated in calcified matrix. Most hypertrophied chondrocytes in the centrum showed in various stage of degeneration in disorderly arrangement. At the blind end of deep canal, osteogenic cells, osteoblasts and chondroclasts were observed. Resorption of unmineralized cartilage septa was undertaken by perivascular cells within cartilage canals. The ruffled border of the chondroclast was restricted to resorption site of calcified cartilagenous matrix. The periosteal bone formation was followed by the appearance of primary center of the centrum at 120 mm fetus. The osteoblasts of the perichondrium started to lay down a thin membranous bony lamella on the outer surface of the osseous trabeculae of the centrum. The processes of bone formation in the vertebral bodies were found to possess morphological similarities to that occurring at secondary center of the epiphysis of a long bone. These results indicate that the connective tissue cells within the cartilage canals proliferate and differentiate into osteoblasts at the site of endochondral ossification of the vertebrae.

• The korean journal of orthodontics
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• v.26 no.2 s.55
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• pp.187-196
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• 1996

Underlying malocclusions and dentofacial deformities are often related to variations in the craniofacial development. Type I and type II collagens are considered the major collagens of bone and cartilage respectively. Monitoring the patterns of those protein expressions during development will Provide a basis for the understanding of normal and abnormal growths. This study was undertaken to investigate the morphogenetic changes and the expression patterns of type I and II collagen proteins involved in the developing mandible of human embryos and fetuses. 50 embryos and fetuses were studied with Hematoxylin and Eosin, Alcian, blue-PAS, Masson Trichrome, md Immunohistochemical stains. The results were as follows : 1. A 13.5 mm embryo showed the stomatodeum with dental lamina, maxillary and mandibular processes. Meckel's cartilage appeared in the mandibular arch of a 20.5 mm embryo. New bone formation was bilaterally initiated at the outer side of middle portion of Meckel's cartilage of 22-38 mm embryos. 2. Meckel'cartilage was resorbed at the 15th week fetus. The endochondral ossification was observed where there was direct replacement of cartilage by bone. Meckel'cartilage disappeared and membraneous ossification were observed at the 25th week. 3. Before the appearance of Meckel's cartilage, the expression of type I collagen was moderate at the odontogenic epithelium of maxillary & mandibular process, but mild for the expression of type II collagen. 4. During the appearance of Meckel's cartilage and new bone formation, the immunoactivity of type II collagen was more expressed than type I collagen at the Meckel's cartilage and new bone. 5. During intrarmembranous bone formation, the expression of type II collagen was rare in the bony trabeculae. There was a switch for the expression of collagens from type II to type I during the appearance of Meckel's cartilage.