Size control of silica nanoparticles and their surface treatment for fabrication of dental nanocomposites.

Nearly monodispersed silica nanoparticles having a controlled size from 5 to 450 nm were synthesized via a sol-gel process, and then the optimum conditions for the surface treatment of the synthesized silica nanoparticles with a silane coupling agent (i.e., 3-methacryloxypropyltrimethoxysilane (gamma-MPS)) were explored to produce dental composites exhibiting enhanced adhesion and dispersion of silica nanoparticles in the resin matrix. The particle size was increased by increasing amounts of the catalyst (NH4OH) and silica precursor (tetraethylorthosilicate, TEOS) and by decreasing the amount of water in the reaction mixtures regardless of solvents used for the synthesis. The particle size prepared by using ethanol as a solvent was significantly larger than that prepared by using methanol as a solvent when the composition of the reaction mixture was fixed. The nanosized particles in the 5-25 nm range were aggregated. The amount of grafted gamma-MPS on the surface of the synthesized silica nanoparticles was dependent on the composition of the reaction mixture when an excess amount of gamma-MPS was used. When surface treatment was performed at optimum conditions found here, the amount of the grafted gamma-MPS per unit surface area of the silica nanoparticles was nearly the same regardless of the particle size. Dispersion of the silica particles in the resin matrix and interfacial adhesion between silica particles and resin matrix were enhanced when surface treated silica nanoparticles were used for preparing dental nanocomposites.