Bonded amalgam restorations: a comparative study of glass-ionomer and resin adhesives

This study assessed the effectiveness of a glass-ionomer liner/base (Vitrebond) and two adhesive resins (Amalgambond and Panavia Ex) in bonding amalgam to enamel/dentine cavities in vitro. Restorations placed without any intermediary, or with varnish, served for comparison purposes. Standardised unretentive cavities on the buccal sides of a total of 78 extracted human molar teeth were prepared to receive the restorations. After application of the adhesive materials (without light curing the Vitrebond), the cavities were filled with amalgam (Dispersalloy). Each specimen was stored for 24 hours in distilled water at 37 degrees C. The amalgam restorations were then pulled from the cavities using an Instron machine and the retentive strength values were recorded. The results showed that any of the three adhesive intermediary agents substantially enhanced the retention of the amalgam restorations. The Vitrebond specimens had the highest mean retentive strength value (133 N), followed by Amalgambond (18% lower) and Panavia Ex (38% lower); the difference between the value for the Vitrebond specimens and that for the Panavia Ex specimens was statistically significant. The Vitrebond specimens failed due to gross enamel fractures and a cohesive failure of the glass-ionomer layer. The Amalgambond specimens failed at the resin/amalgam interface, while the Panavia Ex specimens showed enamel fractures and failure at the resin/dentine interface. It appears that Vitrebond has the potential for being an effective amalgam adhesive in vivo.