Nanoparticle Filled Polymer-Particle Composites

OBJECTIVES: Dental composites require good hardness and strength. Fillers, as high performance additives, can play an important role in polymer composite applications, including dental composites. METHODS: This work synthesized metal oxide nanorods/nanofibers by a simple hydrothermal process. The particles' surface composition was then chemically altered with the goal of improving dispersion and polymer-composite performance. Surface modified and unmodified filler particles were characterized, incorporated as neat and modified particles into BisGMA-TEGDMA, epoxy, and Silmix (®3M-ESPE) cationic light-curable dental composites, and the effects on composite green viscosity, hardness, and tensile and flexural strength properties assessed. RESULTS: Shaped nanoparticles provide enhanced reinforcement compared to conventionally ground or spherical fillers, even where the conventional filler has nanoparticle content. Surface modification, where bonded polymer-reactive groups were bonded to the particle surfaces, had two functions: The organic groups provided enhanced dispersion and reduced dispersion viscosity while the reactive groups enhance interfacial bond strength and cohesive strength. CONCLUSIONS: Nanofillers have a high interfacial contact area to filler volume ratio and, properly dispersed, are more efficient for reinforcing composites compared to conventional fillers. Surface-modified particles were improved in their ability to prevent retarding of polymerization, for promoting composite strength, and also for improving dispersibility and reducing green viscosity. This work was supported in part by DOD Grant W81XWH (DOD bone stabilizer) and NIH-NIDCR Grant R21 DE018336 (R21 composite).