Effect of Water Storage on the Microtensile Bond Strength of Composite Resin to Dentin Using Experimental Rigid Rod Polymer Modified Primers

Purpose: Rigid rod polymers (RRPs) can be used as reinforcing fillers, comparable to inorganic particulate fillers, with the exception that RRP fillers can be dissolved from the surface, thus potentially improving their adhesion to polymer matrix. This study evaluated the effect of water storage on the microtensile bond strength (µTBs) of composite resin to dentin using experimental RRP modified primers. Materials and Methods: Experimental primers were fabricated by dissolving RRP (Parmax, 1240, Mississippi PolymerTechnologies, USA) into dichloromethane (DCM) and mixing it with the monomers bis[2-(methacryloyloxy)- ethyl]phosphate (BMEP) and 3(methacryloyloxy)-propyltrimethoxysilane (MPS). Three experimental primers were prepared with different proportions for each dentin substrate. The same commercial etch-and-rinse adhesive was used with each group. Surfaces of human molars were wet ground occlusally. The experimental primers were applied onto dentin prior to light polymerization of the incremental composite resin buildup. Teeth were sectioned after 48 h, 6 months, or 12 months of water storage and then tested with the microtensile tester (Dillon Quantrol, Bisco). Results: ANOVA revealed that the solvent:monomer ratio and RRP had a significant effect (p 0.05) on bond strength in 48-h groups (3-way ANOVA). Increasing the solvent:monomer ratio and addition of RRP into primers increased the µTBS values. However, long-term water storage decreased the µTBS values in the high solvent:monomer ratio group. In the other groups, water storage did not decrease the µTBS values. Conclusion: One-year water storage lowered the dentin bond strength obtained using the primer with a high solvent:monomer ratio, whereas no decrease of bond strength was observed for the other study groups or for the control group. Keywords: adhesion, dentin, primer, rigid rod polymer