Whisker-reinforced dental core buildup composites: Effect of filler level on mechanical properties

The strength and toughness of dental core buildup composites in large stres s-bearing restorations need to be improved to reduce the incidence of fract ure due to stresses from chewing and clenching. The aims of the present stu dy-were to develop novel core buildup composites reinforced with ceramic wh iskers, to examine the effect of filler level, and to investigate the reinf orcement mechanisms. Silica particles were fused onto the whiskers to facil itate silanization and to roughen the whisker surface for improved retentio n in the matrix. Filler level was varied from 0 to 70%. Flexural strength, compressive strength, and fracture toughness of the composites were measure d. A nanoindentation system was used to measure elastic modulus and,hardnes s. Scanning electron microscopy (SEM) was used to examine the fracture surf aces of specimens. Whisker filler level had significant effects on composit e properties. The flexural strength in MPa (mean +/- SD; n = 6) increased f rom (95 +/- 15) for the unfilled resin to (193 +/- 8) for the composite wit h 50% filler level, then slightly decreased to (176 +/- 12) at 70% filler l evel. The compressive strength increased from (149 +/- 33) for the unfilled resin to (282 +/- 48) at 10% filler level, and remained equivalent from 10 to 70% filler level. Both the modulus and hardness increased monotonically with filler level. Ln conclusion, silica particle-fused ceramic single-cry stalline whiskers significantly reinforced dental core buildup composites. The reinforcement mechanisms appeared to be crack deflection and bridging b y the whiskers. Whisker filler level had significant effects on the flexura l strength, compressive strength, elastic modulus, and hardness of composit es. (C) 2000 John Wiley & Sons, Inc.