Development of Dentin Bonding System

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In this study, a series of five ED Primer II Liquid A primers in different stages of degradation, where the HEMA employed in the Liquid A primer had been hydrolyzed by 4.7,39.2,61.9,66.7 and 66.8 %, respectively, were prepared. The degradation stage effects of the ED Primer II Liquid A primers used for resin core restoration, on the dentin bond durability were examined. The initial shear bond strength remained unchanged at approximately 12 MPa until the degradation stages of the altered Liquid A primers ranged from 4.7 to 61.9 %, even though the quality of the resin hybridized collagen layer had decreased. However, the application of thermo-cycling resulted in specific decreases in the bond strength and degradation of the resin hybridized collagen layer. The degree of reduction in the bond strength was strongly dependent on the degradation stage of the hydrolyzed Liquid A primer.Furthermore, three experimental self-etching primers - consisting of NMωR with different methylene chain lengths and NMGIy - were developed. This was done with a view to investigating the effect of methylene chain length in NMωP derivatives on the chemical nature of calcium salts, as well as its effect on the bond strengths of resin to enamel and dentin. NMR analysis data showed that NMωPs decalcified tooth components with formation of calcium salts, which changed from calcium hydrogen phosphonate to calcium phosphonate with increase in methylene chain length within the NMωP structure. Disparity in calcium salt formation was related to increases in bond strength to enamel from 18 to 24 MPa, reflecting an increase in the hydrophobicity of NMωP calcium salt. However, bond strength to dentin remained unchanged at approximately 22 MPa. This difference probably arose from the dissimilar locations at which NMωP calcium salts were deposited on enamel and dentin.