Resistance to degradation of resin-dentin bonds using a one-step HEMA-free adhesive.

Objective: To evaluate the resistance to degradation of resin-dentin bonds formed with a one-step acetone-containing and HEMA-free adhesive.
Methods: Flat, mid-coronal dentin surfaces were bonded with G Bond under dry and wet conditions. The bonded teeth were subjected to fatigue loading (90 or 250 N) using 5000 or 50000 cycles (at 3.0 Hz) and to chemical degradation (10% NaOCl immersion for 5 h). Specimens were sectioned into beams and tested for microtensile bond strength. Fractographic analysis was performed by scanning electron microscopy (SEM). Additional specimens were processed for morphological examination of the interfaces.
Results: Bond strength significantly decreased after the chemical challenge (p<0.05), but not after load cycling. Dentinal moisture did not affect bond strength. Most of the recorded failures were adhesive and located at the top of the hybrid layer. A poorly infiltrated hybrid layer with bubbles entrapped within the adhesive was observed in all groups.
Conclusions: A discrepancy between water/solvent evaporation rate and convective and evaporative water fluxes from the underlying dentin may be responsible of the droplet formation within the adhesive layer, thus reducing bond strength. A "stress relieving" effect may occur during loading. A loss of bonding effectiveness is expected overtime, mainly due to chemical degradation of the hybrid layer.