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 (Herculit e, Z100) mediated by three universal bonding agents (All-Bond 2, Amalg ambond, and Scotchbond Multi-Purpose). Cylinders of dental composite r esin were formed on, and bonded to, flat amalgam surfaces. Prior to bo nding, the amalgam surfaces were: a) ground flat with the grinding lin es oriented parallel to the direction of the shear stress; b) ground f lat, with the grinding lines oriented perpendicular to the direction o f the shear stress; or c) ground flat and then sandblasted using 50 mu m Al2O3. A computerized Universal Testing Machine was used to determi ne the 1-, 7-, and 30-day shear bond strength of 162 samples (sin per group) that were stored in distilled water at 37 degrees C. The result s, which were statistically analyzed by performing a three-way analysi s of variance (ANOVA) and 27 one-way ANOVA followed by modified (Bonfe rroni) t-tests for between-group comparisons (alpha = 0.05), have show n that: 1) sandblasting resulted in higher shear bond strength than gr inding, except for 1-day All-Bond 2, where no differences were identif ied; 2) there was no difference in the shear bond strength between sam ples with parallel or perpendicular ground surfaces for a given bondin g system and storage time; 3) for All-Bond 2, the 7-day shear bond str ength of parallel and perpendicular ground samples dropped to half of the 1-day values, while the sandblasted samples showed a constant, hig h shear bond strength over 30 days, 4) for Amalgambond, the shear bond strength of parallel, perpendicular, and sandblasted samples was cons tant over 30 days; and 5) for Scotchbond Multi-Purpose, a sharp drop i n the 7-day shear bond strength was recorded for all the samples, irre spective of amalgam surface preparation.