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-uni t applications, Recent studies showed that the addition of ceramic whiskers significantly reinforced resin composites. The aim of the present study wa s to use a silicon carbide whisker-silica particle mixture to reinforce res in composites, and to investigate the effect of whisker-silica mixture heat -treatment on composite properties. The whiskers were blended with silica p articles and were thermally fused in an attempt to roughen the whiskers for improved retention in the matrix. The mixtures were heat-treated at temper atures of 500, 650, 800, 950, and 1100 degreesC for 10 min. 30 min, and 3 h . The mixtures were then silanized, incorporated into a dental resin, and t he paste was placed into 2 x 2 x 25 mm molds and heat-cured at 140 degreesC 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 con trols. Two-way ANOVA showed that there was no significant effect from tempe rature or time. Therefore, all the whisker-silica mixture samples were comb ined into one group (n = 96), and compared to composites filled with silica only; or whisker only, and the two indirect control composites. The whiske r-silica mixture group had a flexural strength (mean +/- SD) of(186 +/- 24) MPa, significantly higher than (99 +/- 29) MPa for silica only, (131 +/- 2 2) MPa for whisker only, and (109 +/- 23) MPa and (114 +/- 18) MPa for the two indirect composites (Tukey's multiple comparison test; family confidenc e coefficient = 0.95). Similar results were obtained on work-of-fracture. S canning electron microscopy revealed rough fracture surfaces for the whiske r-silica a composites, indicating crack deflection and bridging by whiskers as toughening mechanisms, VVhisker-silica mixture minimized whisker entang lement and enhanced whisker-resin bonding, resulting in substantially stron ger and tougher dental resin composites. (C) 2000 John Wiley & Sons. Inc. J Biomed Res Mater Res(Appl Biomater) 58: 81-87. 2001.