| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1989: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1988: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
Crown cementum of berbivores is formed successively showing no pathological change and their filling cementum between occlusal crests is abraded leaving depressions or caves in occlusal surface, which serves grinding food, while human cementum exposed in the oral cavity lapse into pathological state in which cells and fibers in the surface of the cementum denature and the substances from plaque penetrate deeply into the cementum.
Comparative studies on the crown cementum of mandibular molars in cattle, horses and sheep by microradiograpby, light microscopy, scanning and transmission electron microscopy revealed the following results.
1.Cementoenamel junction in the crown of horses bad the unique structure that was different from that of cattle. In cattle the hemispherical projection of cementum fitted into the recesses of about 4 um in diameter on the surface of enamel. In horses the surface of enamel had a number of resorption concavities whose outline was scalloped. These structures se
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rved the firm connection between cementum and enamel.
2.Pericoronal cementum had a laminated structure which was supposed to be periodically formed by the cementoblasts in gingiva and periodontal ligament at the time of eruption. Sharpey's fibers penetrated through the whole layers of pericoronal cementum.
3.Though the filling cementum was in contact with pericoronal cementum at forming stage, in the abraded functional teeth they lost the continuity. However, the filling cementum was always free from Sharpey's fibers. The small arteries of about 200 um were found at the center of the filling cementum, and arterioles of about 30um branched toward the cementoenamel junction. Numerous cementoblasts were also found in the filling cementum. Calcification was observed in lacunae and around vessels, which suggested that reticular fibers were initially formed around vessels, degenerated cells or bacteria in lacunae,as the nucleus.
4.Crown cementum was formed by cementoblasts differentiated from the mesenchymal cells in the dental follicle, which was the same process as that in the cementum covering foot. The initial formation of crown cementum was found at the bottom of the occlusal groove. Less
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