Development of bonding system for altered dentin

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It is well understood that the bond strength of resin to the dentin decreased when the storage period of self-etching primers is prolonged, due to the alteration of the functional monomers employed in the primer.In this study, we prepared a series of five altered self-etching primers with different degradated stages. The degradation stage effects of self-etching primer on the bond strength of resin to the dentin were examined to understand the degradation mechanism on the dentin bonding through the alteration of the functional monomer employed in self-etching primer.When the fresh liquid A, where the HEMA had hydrolyzed by 5%, was applied to the ED Primer II bonding system, the mean bond strength of resin to dentin was approximately 12 MPa. This initial mean bond strength to the dentin, conditioned by the altered ED Primer II, was maintained until the HEMA utilized in the liquid A had hydrolyzed by 62%.Furthermore, when the amount of hydrolyzed HEMA become more than 62%, the bond strength dramatically dropped down to 8 MPa. This dramatic decrease was probably due to the degradation of the priming efficacy of the dentinal collagen network by the HEMA.The degradation of the liquid A, caused by the hydrolysis of the methacryloxy ester portion in the HEMA, induces a decrease in the bond strength. Specifically, when HEMA in the liquid A had hydrolyzed by 67%, the dramatic decrease in the bond strength to the dentin was observed. We found the initial bond strength was maintained until the amount of hydrolyzed HEMA reached to 62%.