Objectives: To examine the effects of an additional low viscosity resin coating on the bonding of 1-step and 2-step self-etching resin cements to dentin.
Methods: Resin composite overlays were constructed and cemented to the surfaces using either Panavia F (Kuraray) or Bistite II DC (Tokuyama) resin cements mediated by their respective one-step or two-step self-etch adhesives to deep human dentin. Experimental groups were prepared the same way, except that an additional layer of bonding resin (Scotchbond Multi-Purpose Plus, 3M ESPE) was placed on the bonded dentine surface before luting the overlays with the respective resin cements. Microtensile bond strength evaluation was performed after 24 h of water storage, using beams of approximately 0.8 mm2 in cross-sectional area. Fractured interfaces were examined with SEM, and intact specimens were examined using TEM after exposure to ammoniacal silver nitrate.
Results: Two-way ANOVA showed significant interactions between materials and bonding protocols (p<0.05). When bonded according to manufacturer’s directions, Panavia F produced significantly lower bond strength than Bistite II DC (p<0.05). The placement of an additional layer of bonding resin improved significantly the bond strengths of Panavia F (p<0.05), but not of Bistite II DC (p>0.05). SEM of fractured surfaces in Panavia F showed rosette-like features that were exclusive for specimens bonded according to manufacturer’s directions. Such features corresponded with TEM of intact interfaces that showed more nanoleakage associated with the more permeable adhesive interface. The application of an additional layer of bonding resin reduced the amount of silver impregnation for both adhesives, suggesting that reduced permeability of the adhesives resulted in improved coupling of the resin cements to dentin.
Conclusions: Placement of an intermediate layer of bonding resin between the bonded dentin surface converts Panavia F from a 1-step to a 2-step self-etching resin cement and improves its coupling to dentin.