Flexural property of resin-infiltrated demineralised dentin after water storage

Objective: 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 examined whether a similar relation exists when adhesive resins were used to create resin-infiltrated dentin, and how changes in the flexural modulus of resin-infiltrated dentin after water storage were affected by their hydrophilic characteristics. Methods: Three increasing 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 4 weeks of water storage.   Result: Flexural modulus reductions in macro-hybrid layers were related to and more extensive than reductions in the corresponding neat polymer beams. Macro-hybrid layers made of more hydrophilic resin (i.e. resin C) exhibited higher percent reductions in flexural modulus, with the rate of reduction being proportional to the Hoy's solubility parameters for total intermolecular attraction forces (d_t) and polar forces (d_p) of the macro-hybrid layers.

Conclusion: Within the limits of using a macro-hybrid layer model as a substitute for authentic microscopic hybrid layers, this in vitro modeling study demonstrated that reductions in the flexural modulus of macro hybrid layers were lower than that of neat resins after 4 weeks of water storage.  This model permits convenient mechanical testing of “hybrid layer” using commonly available equipment.  Supported by grant DE014911 from NIDCR (DP, PI).