Characterization of dentin-bonding-amalgam interfaces

Applying a bonding agent and a resinous adhesive layer before amalgam condensation has become a common clinical procedure. However, interactions between the different interfaces formed, and the extent of sealing obtained, have not been extensively studied. This study characterized the interfaces formed in the bonded amalgam restoration. Specifically, the individual contributions of the bonding agent (One-Step) and the adhesive resin (Resinomer) were examined, along with their mode of application on the prevention of microleakage and the formation of a tight, continuous adhesion to amalgam. To this end, a dye penetration assay and scanning electron microscopy (SEM) were used, including high resolution elemental analysis, for the characterization of the sealing properties and the interface structure obtained following various procedures of applying amalgam adhesives. Results indicated that placing bonding material under the amalgam restoration is essential to preventing microleakage. When condensed against uncured or cured adhesive material, the adhesive resinous glass layer creates a thick interface with protrusions and inclusions in the amalgam, though microleakage studies indicate that condensation over the uncured adhesive results in a better seal than that of the cured adhesive. SEM combined with elemental analysis indicates that the adhesion between amalgam and adhesive material is mainly of mechanical character and is formed by interdigitations of the adhesive material protruding into the amalgam. Gaps formed at the various interfaces in the different modalities could be localized. In addition, resinous glass composite alone, without bonding, was found to provide an unacceptable degree of sealing between the tooth and amalgam. The clinical significance of these findings is further discussed.