Plasticization of polymers by water sorption lowers their mechanical properties in a manner that is predictable by the polarity of their component resins. This study tested the hypothesis that when adhesive resins were used to create resin-infiltrated dentin, the reductions in their flexural moduli after water storage would be lowered proportional to their hydrophilic characteristics. Three increasingly hydrophilic resin blends were used to fabricate polymer beams and macro-hybrid layer models of resin-infiltrated dentin for testing with a miniature three-point flexure device, before and after 1-4 weeks of water storage. Flexural modulus reductions in macro-hybrid layers were related to, and more extensive than, reductions in the corresponding polymer beams. Macro-hybrid layers that were more hydrophilic exhibited higher percent reductions in flexural modulus, with the rate of reduction proportional to the Hoy's solubility parameters for total intermolecular attraction forces (delta(t)) and polar forces (delta(p)) of the macro-hybrid layers.

This study evaluated the effects of two exogenous enzymes on the resin-dentin interface. Collagenase (Col) and acetylcholinesterase (Ach) were used to simulate salivary enzymes and accelerate the aging process of the bonding interfaces. Four adhesives, Adper Single Bond 2 (SB), Clearfil SE Bond (SE), Clearfil tri-S Bond (S3) and G-Bond (G), were bonded to the dentin surfaces. After storage in water with collagenase or acetylcholinesterase, the specimens were examined using a microtensile bond strength test (MTBS). Nanoleakage patterns were observed with a scanning electron microscope (SEM). The MTBS results demonstrated significantly lower bond strengths in the groups stored with either enzyme than in water. SB exhibited severe degradation after exposure to collagenase, while G showed severe degradation after exposure to acetylcholinesterase. All of the self-etch systems (SE, S3 and G) exhibited water-tree patterns within the adhesive layer when immersed in water for three months. The etch-and-rinse system (SB) showed nanoleakage within the hybrid layer and the adhesive.