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.