Functional monomers chemically interact with hydroxyapatite that remains within submicron hybrid layers produced by mild self-etch adhesives. The functional monomer 10-MDP interacts most intensively with hydroxyapatite, and its calcium salt appeared most hydrolytically stable, as compared with 4-MET and phenyl-P. We investigated the hypothesis that additional chemical interaction of self-etch adhesives improves bond stability. The micro-tensile bond strength (muTBS) of the 10-MDP-based adhesive did not decrease significantly after 100,000 cycles, but did after 50,000 and 30,000 cycles, respectively, for the 4-MET-based and the phenyl-P-based adhesives. Likewise, the interfacial ultrastructure was unchanged after 100,000 thermocycles for the 10-MDP-based adhesive, while that of both the 4-MET- and phenyl-P-based adhesives contained voids and less-defined collagen. The findings of this study support the concept that long-term durability of adhesive-dentin bonds depends on the chemical bonding potential of the functional monomer.

The purpose of this study was to evaluate the long-term durability of in vivo bond strengths and the morphological changes of interfaces between dentin and two adhesive systems. Class V preparations were prepared on the facial surfaces of 14 intact teeth of two monkeys and restored with a combination of Unifil Bond/Z250 or Single Bond/Z250. One year later, 10 additional teeth were restored with the same materials and the monkeys were killed after 24 h. All of the restored teeth were subjected to microtensile bond strength ( micro TBS) testing. The debonded surfaces of the dentin sides were morphologically observed using Fe-scanning electron microscopy (SEM), as were the polished cross-sections of resin-dentin interfaces. For both Unifil Bond and Single Bond, the micro TBS at 24 h was significantly higher than that at 1 yr. Fe-SEM observations of polished cross-sectioned and fractured surfaces showed that porosity within the hybrid layers produced by Single Bond increased over time. However, the interface produced by Unifil Bond revealed no noticeable changes in morphology between 24-h and 1-yr specimens. It is concluded that even though the bond strengths of both adhesive systems declined over time, the bonding interface using self-etching primers was relatively stable over time compared to the wet bonding system.