Testing mode and surface treatment effects on dentin bonding

The goal of this project was to evaluate the effect of the following variables on shear dentin-bonding test results: mode of testing (cyclic fatigue versus static loading), surface treatments (32% phosphoric acid, 10% phosphoric acid, and no treatment [unetched]), and type of shear test (traditional planar versus push-out). All teeth were stored in distilled water and tested in a shear mode at a loading rate of 2 mm/min. The specimens were loaded in static or cycled for 1000 cycles using a staircase approach or until fracture, whichever occurred first. On samples with etched dentin surfaces, the push out test did not demonstrate a significant difference in measured bond strength when compared with results from the planar test, although sample preparation was more labor-intensive. The bond strength resulting from cyclic fatigue of the etched specimens was approximately 51% of the static loading value. Ten percent phosphoric acid was as effective as 32% phosphoric acid for dentin bonding. Finite-element analysis indicated that the traditional planar shear test produces flexure of the specimen and high tensile stress magnitudes within the resin bonding layer. The push-out test produces elevated compressive stresses localized in the composite along the circumference of the punch. Shear stresses in the resin bonding layer are similar for both testing methods at the same loading element contact force.