The influence of long term water immersion on shear bond strength of amalgam repaired by resin composite and mediated by adhesives or resin modified glass ionomers

Objective: To assess the shear bond strength between amalgam and resin composite mediated by either multipurpose adhesive systems or RMGI when subjected to long term immersion in saline. Methods: Part I: Cylindrical specimens (6 mm × 6 mm) composed of equal parts of sandblasted set amalgam (Oralloy) and composite (Z-100), with a thin layer of either Scotchbond Multipurpose, All Bond 2, Amalgam Bond Plus, High Q Bond Plus or Vitrebond in between were fabricated (n = 100 × 5). Each group was divided into 3 subgroups, immersed in saline at 37 °C for either 48 h, 3 or 6 months, followed by thermocycling (5000; 5/55°C) and shear bond strength testing (SBS). Part II: Identical specimens were fabricated with intermediary of either Ketac Cem, Fuji Lining LC, Rely X Luting, Fuji Plus or Meron Plus (n = 100 × 5). Immersion periods, followed by thermocycling and SBS testing as in Part I. Two representative specimens from each subgroup were sectioned and inspected under SEM. Results: The two classes of intermediary agents yielded SBS which differed mainly in the 6 months incubation period. While multipurpose adhesives provided SBS values of ∼9-10 MPa RMGI provided higher SBS of ∼16 MPa. All Bond 2 and Amalgam Bond Plus exhibited deterioration of SBS during the 6 month period as well as Rely X Luting. Gap sizes between 0.5 and 3 μm exist between all intermediaries and the amalgam; on the other hand all intermediaries exhibit gap-free interfaces between the adhesives/RMGI and the composite. Conclusions: Vitrebond in particular and RMGIs in general can serve as an excellent coupler of resin composite to amalgam, providing a durable bond.