On the durability of resin–dentin bonds: Identifying the weakest links

Fatigue of resin–dentin adhesive bonds is critical to the longevity of resin composite restorations.ObjectivesThe 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”.MethodsBonded 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.ResultsThe 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 (ΔKth) of the SB interface was significantly greater (p ≤ 0.01) than that of the SBMP, whereas the ΔKth of the interfaces was more than twice that of the parent adhesives.SignificanceCollagen 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.