In vitro degradation of resin–dentin bonds analyzed by microtensile bond test, scanning and transmission electron microscopy

Our knowledge of the mechanisms responsible for the degradation of resin–dentin bonds are poorly understood. This study investigated the degradation of resin–dentin bonds after 1 year immersion in water. Resin–dentin beams (adhesive area: 0.9 mm2) were made by bonding using a resin adhesive, to extracted human teeth. The experimental beams were stored in water for 1 year. Beams that had been stored in water for 24 h were used as controls. After water storage, the beams were subjected to microtensile bond testing. The dentin side of the fractured surface was observed using FE-SEM. Subsequently, these fractured beams were embedded in epoxy resin and examined by TEM. The bond strength of the control specimens (40.3±15.1 MPa) decreased significantly (p<0.01) after 1 year of water exposure (13.3±5.6 MPa). Loss of resin was observed within fractured hybrid layers in the 1 year specimens but not in the controls. Transmission electron microscopic examination revealed the presence of micromorphological alterations in the collagen fibrils after 1 year of water storage. These micromorphological changes (resin elution and alteration of the collagen fibrils) seem to be responsible for the bond degradation leading to bond strength reduction.