Effect of universal testing machine crosshead speed on the shear bond strength and bonding failure mode of composite resin to enamel and dentin.

An investigation was conducted to determine if testing machine crosshead speed influenced shear bond strength (SBS) or the failure mode of composite bonded to enamel and dentin. Composite cylinders were bonded to 50 enamel and 50 dentin surfaces and thermocycled. Groups of 10 samples were debonded at speeds of 0.1, 0.5, 1.0, 5.0, and 10.0 mm/min. Data were examined with analysis of variance and post-hoc testing. Failure modes were determined using 10x magnification. With enamel, no significant differences in SBS existed, and cohesive vs. adhesive failure modes were similar for all groups. With dentin, the 0.5, 1.0, and 5.0 mm/min samples had significantly higher SBS than the 0.1 and 10.0 mm/min samples (p < 0.05). No other differences in SBS were found. Samples tested at 0.5 mm/min demonstrated strikingly better cohesive vs. adhesive results than all other groups. SBS and cohesive vs. adhesive failures achieved with dentin bonding were significantly affected by crosshead speed.