Study on Restorative and Preventive Methods of Root Surface Caries in vitro.

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In this study the most appropriate methods for evaluating the dentin adhesive agent, improving the marginal closure, and preventing root caries were examined.The results obtained were as follows :1. An accurate, reproducible, and durable adhesive fatigue testing machine was constructed. Four brands of dentine adhesives were evaluated using this machine. The static shear bond strengths of three brands were similar, but the dynamic fatigue shear bond strengths were significantly different from each other, and Liner Bond<@D1(]SY.encircledR.[)@>D1 showed the highest static shear bond strength with no fatigue decline.2. To improve the marginal closure of light-curing resin composite restoration, the three components inclined incremental technique was evaluated. Better marginal closure of resin composite was obtained when the incremental technique was used and the water immersion period was extended.3. To prevent the secondary caries of cast restoration, the APF-lanthanum treatment was applied onto the dentinal cavity walls before cementation. The APF-lanthanum treatment (APF-La Tx) is effective as a pretreatment of the cavity to prevent acid penetration and to preserve the dentin structure.4. To indicate the effectiveness of APF-La Tx onto the dentin surface against demineralization in vitro, a scanning electron microscopic study was performed. Before demineralization, APF-La treated dentin surface was completely covered with a 0.5-1.0 mum thick layer of minute spherical compounds, and these compounds still remained and covered the surface even after demineralization. Dentinal tubules were closed by dentinal plugs. APF-La Tx group showed a shallower lesion formation than the control and APF groups. The APF-La Tx was outstanding with a well preserved surface structure resistant against subsequent acid attack.