Endowing dental resin composites (DRCs) with suitable radiopacity is necessary for clinical diagnosis during treatment of caries. To reach this effect, ZrO2 nanoparticles were introduced into the DRCs in this work after modification with two different methods, one modified with 3-methacryloxypropyltrimethoxysilane (ZrO2@γ-MPS) and the other coated with mesoporous SiO2 and then modified with γ-MPS (ZrO2@m-SiO2@γ-MPS). These ZrO2 nanoparticles were used as functional additives, and the SiO2 nanoparticles were used as the fundamental filler in the preparation of DRCs to study the effects of the surface modification of ZrO2 nanoparticles and the amount of particles added (0, 3, 5, and 7 wt %) on the properties of the DRCs. The DRC containing ZrO2@m-SiO2@γ-MPS showed a higher transmittance, which may be attributed to the fact that the SiO2 coating reduced the refractive index of the nanoparticles and thus decreased the scattering of light within the DRC. The silane polymer film on the surface of ZrO2@γ-MPS nanoparticles acted as a lubricant and decreased the viscosity of DRC, but the DRC containing ZrO2@m-SiO2@γ-MPS showed a higher viscosity due to the presence of a mesoporous structure. The radiopacity value of the DRCs containing the functional additives was close to 1 mm Al, much higher than that of the DRC filled with SiO2 nanoparticles alone (0.74 ± 0.07 mm Al), meeting the requirement of ISO 4049:2009. The surface modification of ZrO2 nanoparticles had no significant influence on the mechanical properties, radiopacity, and cytotoxicity of DRCs (p > 0.05). This study provides useful insight into the design and development of radiopaque DRCs with excellent physical and mechanical properties.
Keywords: dental caries; mechanical properties; mesoporous structure; radiopacity; silica.