Effect of dentin primer on the shear bond strength between composite resin and enamel

The purpose of this investigation was to determine the effect of dentin primers from Scotchbond Multi-Purpose, ProBond, All-Bond 2, and Syntac on the shear bond strength of composite resin to etched enamel. Two groups of extracted human molar teeth with flattened enamel surfaces (n = 12) were randomly assigned to each enamel/dentin bonding system. Following manufacturers' instructions enamel surfaces were etched, rinsed, and dried. Composite bonding procedures were conducted similarly in both groups for each enamel/dentin bonding system, except that in one of the two groups, dentin primer was applied prior to adhesive resin and composite placement. Samples were thermocycled and tested in shear until failure. Fracture analysis was performed on enamel surfaces with both light and scanning electron microscopy. Shear bond values (Mean +/- SD, MPa) were: Scotchbond Multi-Purpose unprimed 22.4 +/- 3.2, primed 17.9 +/- 5.9; ProBond unprimed 19.4 +/- 6.2, primed 18.3 +/- 3.3; All-Bond 2 unprimed 19.0 +/- 3.6, primed 17.3 +/- 3.0; and Syntac unprimed 26.2 +/- 9.0, primed 22.0 +/- 5.4. The only significant difference found between primed and unprimed groups was with Scotchbond Multi-Purpose, though there was a trend for primer application to decrease enamel bond strengths. Fracture surface analysis revealed that most failures were cohesive within the composite resin. These data suggest that the effect of primer on bonded composite resin to etched enamel is material specific.