Resin-based composites have attracted widespread attention in dental restoration because of their distinguished esthetics, biocompatibility, and convenient clinical manipulation. The particle size and the dispersity of inorganic filler are crucial. In this study, size-controlled monodisperse silica nanoparticles (MSNPs) from 20 to 330 nm were efficiently prepared in a high gravity environment using internal circulation rotating packed bed (ICRPB) combined with freeze-drying. As compared to traditional stirred tank reactor, ICRPB had one-third reduction in reaction time and MSNPs with an obviously decreased size from 75 to 35 nm. Furthermore, the mechanical properties of composites were greatly improved with the increased MSNPs content from 40 to 70 wt % and increased first and then decreased with increasing particle size, reaching the maximum at 80 nm. Due to the excellent dispersity, the maximum MSNPs content was 30% higher than commercial silica nanoparticles with the same size, thereby endowing composites with better properties.