Whisker-reinforced heat-cured dental resin composites: Effects of filler level and heat-cure temperature and time

Currently available dental resin composites are inadequate for use in large stress-bearing crown and multiple-unit restorations. The aim of this study was to reinforce heat-cured composites with ceramic whiskers. It was hypot hesized that whiskers substantially strengthen heat-cured composites. It wa s further hypothesized that whisker filler level and heat-cure temperature and time significantly influence composite properties. Silica particles wer e fused onto the whiskers to facilitate silanization and to roughen the whi skers for improved retention in the matrix. The whisker filler mass fractio n was varied from 0% to 79%, the heat-cure temperature from 80 degrees C to 180 degrees C, and cure time from 10 min to 24 hrs. Flexural strength, wor k-of-fracture, and fracture toughness of the composites were measured, and specimen fracture surfaces were examined with scanning electron microscopy. Filler level had a significant effect on composite properties. The whisker composite with 70% filler level had a flexural strength in MPa (mean +/- S D; n = 6) of 248 +/- 23, significantly higher than 120 +/- 16 of an inlay/o nlay composite control and 123 +/- 21 of a prosthetic composite control (Tu key's multiple comparison test; family confidence coefficient = 0.95). Heat -cure time also played a significant role. At 120 degrees C, the strength o f composite cured for 10 min was 178 +/- 17, lower than 236 +/- 14 of compo site cured for 3 hrs. The strength of whisker composite did not degrade aft er water-aging for 100 d. In conclusion, heat-cured composites were substan tially reinforced with whiskers. The reinforcement mechanisms appeared to b e whiskers bridging and resisting cracks. The strength and fracture toughne ss of whisker composite were nearly twice those of currently available inla y/onlay and prosthetic composites.