The objectives were to characterize the fatigue and fatigue crack growth resistance of resin–dentin bonds achieved using two different commercial adhesives and to identify apparent “weak-links”.

Bonded interface specimens were prepared using Adper Single Bond Plus (SB) or Adper Scotchbond Multi-Purpose (SBMP) adhesives and 3M Z100 resin composite according to the manufacturers’ instructions. The stress-life fatigue behavior was evaluated using the twin bonded interface approach and the fatigue crack growth resistance was examined using bonded interface Compact Tension (CT) specimens. Fatigue properties of the interfaces were compared to those of the resin–adhesive, resin composite and coronal dentin.

The fatigue strength of the SBMP interface was significantly greater than that achieved by SB (p ≤ 0.01). Both bonded interfaces exhibited significantly lower fatigue strength than that of the Z100 and dentin. Regarding the fatigue crack growth resistance, the stress intensity threshold (ΔK_th) of the SB interface was significantly greater (p ≤ 0.01) than that of the SBMP, whereas the ΔK_th of the interfaces was more than twice that of the parent adhesives.

Collagen fibril reinforcement of the resin adhesive is essential to the fatigue crack growth resistance of resin–dentin bonds. Resin tags that are not well hybridized into the surrounding intertubular dentin and/or poor collagen integrity are detrimental to the bonded interface durability.