Dentin bonding performance of experimental one-step adhesives after incorporation of POOH–SiO2 nanoparticles

This study investigated the effect of adding different concentrations of phosphate-grafted-silica nanoparticles (SiO₂–POOH) on dentin bond strength of experimental one-step self-etching adhesives (1-SEAs). Phosphate functional group was grafted onto silica nanoparticles through the free radical polymerization of an acid phosphate monomer [methacryloyloxyethyl dihydrogen phosphate/bis (methacryloyloxyethyl) hydrogen phosphate—HEMA-P] in an alcoholic medium. The resulting SiO₂–POOH was characterized by FTIR spectroscopy. 1-SEA with two different acidic phosphate monomer concentrations (HEMA-P at 0 and 40%?wt) were prepared and SiO₂–POOH was added in 0 (control), 0.1, 0.2, 0.5, 1, 2, 4, 6 and 8wt%. The formulated 1-SEAs were evaluated for shear bond strength to dentin. Statistical comparisons were conducted at 5% significance level. The grafting reaction of SiO₂–POOH was confirmed by FTIR. Compared with the unfilled 1-SEA, the addition of 0.1wt% of SiO₂–POOH nanoparticles resulted in a significant dentin bond strength increase for HEMA-P_40% concentration (p?≤?0.001) while the addition of higher concentration of SiO₂–POOH (0.2, 0.5, 1, 2, 4, 6 and 8wt%) reduced significantly the bond strength. The 1-SEA formulated without an acidic monomer (HEMA-P_0%) did not exhibit bonding to the dentin, irrespective of SiO₂–POOH concentration added. SiO₂–POOH nanoparticles were obtained through graft polymerization of acidic phosphate monomer with silanized SiO₂ nanoparticles. The addition of the 0.1wt% of SiO₂–POOH nanoparticles associated with acidic monomer to 1-SEA improves the bonding effectiveness.