Core-shell structured SiO@ZrO@SiO filler for radiopacity and ultra-low shrinkage dental composite resins.

To overcome the interfacial problem between X-ray radiopaque ZrO fillers and polymer resin in dental composites, monodispersed SiO@ZrO@SiO (SZS) microspheres with narrow size distribution were prepared by a controlled sol-gel method. In the presence of SiO coating layer over SiO@ZrO (SZ) microspheres, they were easily silanized same as SiO microspheres. Ethoxylated bisphenol A dimethacrylate (EBPADMA) with a higher molecular weight and a lower viscosity was used as base resin monomer mixed with a low amount of diluent triethylene glycol dimethacrylate (TEGDMA). Additionally, the addition of a small amount of pore agent acetone dicarboxylic acid (ADCA) produced some voids, thereby effectively reducing the polymerization shrinkage of the resin. The prepared dental composites combining 52 wt% monodispersed silica microsphere, 20 wt% SZS microspheres, exhibited significantly enhanced capacity in radiopacity (higher than tooth enamel) and very low shrinkage (<0.1%). It also has better mechanical properties than resin composites filled with SiO microspheres, and its strength can meet practical applications. The properties of the radiopaque dental composite were to be further tuned by varying the amount of SZS microspheres contents, and the radiopaque resin has an advantage over the commercial one in that it is clinically nondestructive.