Bonding of composite resin to dentin using rigid rod polymer modified primers

This study was conducted to evaluate the microtensile bond strength of composite resin to dentin with experimental rigid rod polymer (RRP) modified primers. RRP fillers are based on long stiff molecules specifically designed to create long polymers with restricted chain movement.

Experimental primers were fabricated by dissolving RRP into dichloromethane (DCM) and further mixing it with monomers: ethylene glycol methacrylate phosphate (EGMP), bis[2-(methacryloyloxy)-ethyl]phosphate (BMEP) and 3(methacryloyloxy)propyltrimethoxysilane (MPS). Eight experimental primers were prepared with different proportions for each dentin substrate. A commercial etch-and-rinse adhesive was used as a control. Surfaces of human molar teeth were wet ground occlusally. The experimental primers were applied onto dentin prior to light polymerization of the incremental composite resin build-up. After 48 hours of water storage, teeth were sectioned and tested with the microtensile tester. Fracture surface analysis and contact angle measurements of adhesive resin were performed. Scanning electron micrographs were taken.

3-way ANOVA revealed that all factors, monomer type, solvent-monomer ratio and RRP, had a significant effect (p < 0.05) on bond strength. Primer with a combination of MPS and dimethacrylate BMEP revealed higher bond values than a mixture of MPS and monomethacrylate EGMP. Increase of the solvent-monomer ratio and addition of RRP into primers increased the microTBS.

The contact angle measurements showed that RRP containing primers enhanced adhesive resin penetration into dentin similar to that of the control primer. Within the limitations of this study, it was concluded that an experimental type of modified RRP-silane-phosphate-acrylate primer was developed with comparable bonding properties to a commercial control.