Influence of the nano-hardness and elastic modulus of carious primary tooth dentin to resin adhesion

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<Objective> :To compare the influence of the hardness and elasticity to resin adhesion between carious and sound dentin.<Results> :1.Development of originally designed jig system for micro-tensile strength Testing :New system for primary teeth has been developed.2.Hardness, elasticity and micro-tensile strengths of the carious and sound primary dentin :Physical properties of extracted primary tooth dentin were lower than permanent tooth dentin, especially for the dentin under the lesion and near me pulp.3.Hardness and elasticity of bonded carious and sound dentin :Clearfil Mega Bond (MB group, Kuraray Co.) and Single Bond (3M ESPE Co.Ltd.) were used. Compared to the dentin beneath the resin/dentin interface, the hardness of the interface dentin were higher and showed contrary results to previously reported permanent teeth. But, Young's modulus of the interface dentin were lower than dentin beneath the interface, same as for permanent teeth. No significant difference was found between the carious and sound groups.4.Micro-tensile bond strength(MTBS) for sound and carious dentin :MB or SB was applied on the extracted primary tooth dentin. Dumbbell-shaped and stick-shaped specimens were prepared. The mean MTBS of both dumbbell-shaped and stick-shaped specimens were low, and under 10MPa. No significant difference was found between the MB and SB, and sound and carious groups.<Conclusion> :When bonded to carious dentin, the HL was thicker, but the MTBS was low in both the carious and sound groups. The properties of primary tooth dentin might differ from permanent dentin, thus treatments designed based on permanent tooth dentin may not be optimized for primary tooth dentin. New system based on the physical properties of primary tooth dentin should be required.