Characterization of dentin-bonding-amalgam interfaces

Applying a bonding agent and a resinous adhesive layer before amalgam conde nsation has become a common clinical procedure. However, interactions betwe en the different interfaces formed, and the extent of sealing obtained, hav e not been extensively studied. This study characterized the interfaces for med in the bonded amalgam restoration. Specifically, the individual contrib utions of the bonding agent (One-Step) and the adhesive resin (Resinomer) w ere examined, along with their mode of application on the prevention of mic roleakage and the formation of a tight, continuous adhesion to amalgam. To this end, a dye penetration assay and scanning electron microscopy (SEM) we re used, including high resolution elemental analysis, for the characteriza tion of the sealing properties and the interface structure obtained followi ng various procedures of applying amalgam adhesives. Results indicated that placing bonding material under the amalgam restoration is essential to pre venting microleakage. When condensed against uncured or cured adhesive mate rial, the adhesive resinous glass layer creates a thick interface with prot rusions 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 mechan ical character and is formed by interdigitations of the adhesive material p rotruding into the amalgam. Gaps formed at the various interfaces in the di fferent modalities could be localized. In addition, resinous glass composit e alone, without bonding, was found to provide an unacceptable degree of se aling between the tooth and amalgam. The clinical significance of these fin dings is further discussed.