The effect of amalgam surface preparation on the shear bond strength between composite and amalgam

The aim of this study was to investigate the effect of amalgam surface preparation on the short-and long-term in vitro shear bond strength between a dental amalgam (Valiant) and two dental composites (Herculite, Z100) mediated by three universal bonding agents (All-Bond 2, Amalgambond, and Scotchbond Multi-Purpose). Cylinders of dental composite resin were formed on, and bonded to flat amalgam surfaces. Prior to bonding, the amalgam surfaces were: a) ground flat, with the grinding lines oriented parallel to the direction of the shear stress; b) ground flat, with the grinding lines oriented perpendicular to the direction of the shear stress; or c) ground flat and then sandblasted using 50 micrometer Al2O3. A computerized Universal Testing Machine was used to determine the 1-, 7-, and 30-day shear bond strength of 162 samples (six per group) that were stored in distilled water at 37 degrees C. The results, which were statistically analyzed by performing a three-way analysis of variance (ANOVA) and 27 one-way ANOVA followed by modified (Bonferroni) t-tests for between-group comparisons (alpha = 0.05), have shown that: 1) sandblasting resulted in higher shear bond strength than grinding, except for 1-day All-Bond 2, where no differences were identified; 2) there was no difference in the shear bond strength between samples with parallel or perpendicular ground surfaces for a given bonding system and storage time; 3) for All-Bond 2, the 7-day shear bond strength of parallel and perpendicular ground samples dropped to half of the 1-day values, while the sandblasted samples showed a constant, high shear bond strength over 30 days, 4) for Amalgambond, the shear bond strength of parallel, perpendicular, and sand blasted samples was constant over 30 days; and 5) for Scotchbond Multi-Purpose, a sharp drop in the 7-day shear bond strength was recorded for all the samples, irrespective of amalgam surface preparation.