| Research Abstract |
We previously found that the bond strength of resin cements except Super Bond on the dentin of the tooth root was lower than that of the tooth crown, using teeth without caries and restorations that were extracted in the dental hospital attached to our department. By electron microscopic observation of the tooth surface treated by the primer of the resin cements except Super Bond, the presence of many smeared layers on the tooth root surface were confirmed. Furthermore, the formed resin tags were long and dense in the tooth crown. These findings suggested that resin tags influenced bond strength. The formation of resin tags depends on the degree of the removal of smeared layers caused after cutting, that is, when the effect of the removal of smeared layers is large, resin tags can be easily formed. Therefore, these results indicated that even if the same treatment agent was used for the same treatment duration, there were differences between the degree of the removal of smeared layers
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in the tooth crown and that of the tooth root, and these differences influenced the bond strength.
We recently confirmed the differences in the smeared layers, and performed experiments to confirm whether the differences were caused by the difference between the component of the tooth crown and that of the tooth root. First, to confirm that a recently developed micro-focus X-ray CT system (Shimazu Corp.) was useful for these purposes, we preliminarily took X-ray of bovine teeth. As a result, differences between the degree of calcification in the tooth crown and that of the tooth root were sufficiently observed, and we are investigating human teeth at present. In regard to the differences in the degree of primer treatment and the thickness of resin-impregnated layers, we measured the hardness of dentin at intervals of 2 nm from the adhesion interface, using an ultra-micro indentation hardness test apparatus : ENT-1100a (Eleonics Corp.). Although no differences in the resin-impregnated layers were observed, the dentin under the resin-impregnated layers was treated deeper in the tooth root. Therefore, there was a strong possibility that differences in bond strength were dependent on the differences in the degree of the formation of treated layers and smeared layers, which were caused by the difference between the component of the tooth crown and that of tooth root. Less
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