Three-body wear of dental resin composites reinforced with silica-fused whiskers

Objective. Recent studies used silica-fused whiskers to increase the strength and toughness of resin composites. This study investigated the three-body wear of whisker composites. It was hypothesized that the whisker composites would be more wear resistant than composites reinforced with fine glass particles, and the whisker-to-silica filler ratio would significantly affect wear. Methods. Silica particles were mixed with silicon nitride whiskers at seven different whisker/(whisker+silica) mass fractions (%): 0, 16.7, 33.3, 50, 66.7, 83.3, and 100. Each mixture was heated at 800 °C to fuse the silica particles onto the whiskers. Each powder was then silanized and incorporated into a dental resin to make the wear specimens. A four-station wear machine was used with specimens immersed in a slurry containing polymethyl methacrylate beads, and a steel pin was loaded and rotated against the specimen at a maximum load of 76 N. Results. Whisker-to-silica ratio had significant effects (one-way ANOVA; p<0.001) on wear. After 4×105 wear cycles, the whisker composite at whisker/(whisker+silica) of 16.7% had a wear scar diameter (mean±sd; n=6) of (643±39) μm and a wear depth of (82±19) μm, significantly less than a wear scar diameter of (1184±34) μm and a wear depth of (173±15) μm of a commercial prosthetic composite reinforced with fine glass particles (Tukey's multiple comparison). SEM examination revealed that, instead of whiskers protruding from the worn surface, the whiskers were worn with the composite surface, resulting in relatively smooth wear surfaces. Significance. Silica-fused whisker reinforcement produced dental resin composites that exhibited high resistance to wear with smooth wear surfaces. These properties, together with the strength and fracture toughness being twice those of current glass particle-reinforced composites, may help extend the use of resin composite to large stress-bearing posterior restorations.