永久歯歯冠部の硬度について
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概要
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Extracted human teeth which were caries-free and with normal appearance were used for the studies. 92 teeth were made up to the specimens. They were cut by means of a high speed carborundum wheel, so to obtain suitable surfaces for investigations. The cut surfaces were bisected through the long axis either in the bucco-lingual or labio-longual plane. The surface of the enamel and dentin of every specimen was artificially ground and polished to the greatest smoothness. The sutdies were conducted by using the Vickers microhardness tester. For the front teeth five places were measured which were cirvical region (both of labial and lingual side) ridge (or cusp), labial and lingual surface. For the posterior teeth 8 places were measured. They are cirvical region, cusps, buccal and lingual surface, bucco-occlusal and lingo-occlusal surface. Many impression points were made to the surface of every specimen from the enamel to the predentin at the places mentioned above with a known load, and so the hardness were determined by measuring those impression points.<BR>As to the enamel region, from the dentino-enamel junction to the enamel surface it was divided into many parts with every width of 300μ. made a layer, b layer etc. the highest was up to 8 layers. As to dentin 5 layers were divided (a-e), at each of that layers the hardness was reseached.<BR>The results are as follows;<BR>1. The hardness of the enamel shows the average 360, the hardness of the dentin fell to the range nearly 60.<BR>2. It was found that the enamel of the anterior teeth have the most hardness at cutting edge, near the neck teil of the tooth have a very low value. The middle value is the portion at the center parts of the labial and lingual surfaces. In the posterior teeth the hardness of enamel have a wide variation of the upper, lower or kinds of teeth.<BR>3. A survey of the results revealed a wide variation in the hardness of the enamel but the hardness of the dentin shows a nearly same value.<BR>4. There was a slight increase in hardness from the predentin near the amelo-dentinal junction towards the outer enamel layer.<BR>5. The sexual difference was found out nothing by the hardness measuring of the enamel and dentin.
- 有限責任中間法人 日本口腔衛生学会の論文