Effect of silicon carbide whisker-silica heat treatment on the reinforcement of dental resin composites

The strength and fracture resistance of dental resin composites need to be improved to extend their use to large stress-bearing crown and multiple-unit applications. Recent studies showed that the addition of ceramic whiskers significantly reinforced resin composites. The aim of the present study was to use a silicon carbide whisker-silica particle mixture to reinforce resin composites, and to investigate the effect of whisker-silica mixture heat-treatment on composite properties. The whiskers were blended with silica particles and were thermally fused in an attempt to roughen the whiskers for improved retention in the matrix. The mixtures were heat-treated at temperatures of 500, 650, 800, 950, and 1100 degrees C for 10 min, 30 min, and 3 h. The mixtures were then silanized, incorporated into a dental resin, and the paste was placed into 2 x 2 x 25 mm molds and heat-cured at 140 degrees C for 30 min. A 3-point flexural test was used to measure flexural strength and work-of-fracture. Two commercial indirect composites were tested as controls. Two-way ANOVA showed that there was no significant effect from temperature or time. Therefore, all the whisker-silica mixture samples were combined into one group (n = 96), and compared to composites filled with silica only or whisker only, and the two indirect control composites. The whisker-silica mixture group had a flexural strength (mean +/- SD) of (186 +/- 24) MPa, significantly higher than (99 +/- 29) MPa for silica only, (131 +/- 22) MPa for whisker only, and (109 +/- 23) MPa and (114 +/- 18) MPa for the two indirect composites (Tukey's multiple comparison test; family confidence coefficient = 0.95). Similar results were obtained on work-of-fracture. Scanning electron microscopy revealed rough fracture surfaces for the whisker-silica composites, indicating crack deflection and bridging by whiskers as toughening mechanisms. Whisker-silica mixture minimized whisker entanglement and enhanced whisker-resin bonding, resulting in substantially stronger and tougher dental resin composites.