Cell differentiation is a very important process in morphogenesis, and epithelial-mesenchymal interaction may play an important role in cell differentiation. Therefore, during development of root dentin, arcllular cementum and periodontal ligament, the changes of the morphology of dental mesenchymal cells and of the distribution of extracellular matrix proteins - type I collagen, type ID[ collagen, and fibronectin(FN) - are investigated using 14-day-old Sprague-Dawley rats.
1. In the zone of Hertwig´s epithelial root sheath, intact epithelial root sheath which is formed with two layers of epithelial a -Rs and covered with basement membranes is observed. Cells of dental follicle and of dental papilla adjacent to the epithelial root sheath are not differentiated yet. In the zone of differentiation, odontoblasts and cementoblasts are differentiated. Cells in the middle of the dental follicle are differentiated into fibroblasts. In the zone of formation, dentin and acellular cementum are observed. The fibroblasts in the forming periodontal ligament are oriented obliquely ard synthesize the collagen fibrils parallel to their direction.
2. In the zone of HERS, immunoreactivity of FN is very strong at the inner basement membrane of the HERS. In this zone, immunoreactivity of type Ill collagen in the extracellular matrix is stronger than in other zones.
3. In the zone of differentiation, cell body of odontoblast shows little of immunoreactivity to FN and collagens. But cell membrane of proximal surfaces of odontoblasts shows very strong immunoreactivity to FN. Along the cementoblasts attached root dentin, strong immunoreactivity to FN is shown.
4. In the zone of formation, acellular cementum matrix is stained strongly to FN. Periodontal ligament shows strong immunoreactivity to FN, type I collagen, and type III collagen with their fibrils´ direction. Predentin is stained moderately with FN, type I and type III collagen, but immunoreactivity of mineralized dentin is weaker.
5. Hertwig´ s epithelial root sheath ;plays an important role in cell differentiation by the epithelial-mesenchymal interaction.
Extracellular matrix of the mesenchymal cells seems to affect the cell differentiation directly and/or indirectly.
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