Ceramic whisker reinforcement of dental resin composites

Resin composites currently available are not suitable for use as large stre ss-bearing posterior restorations involving cusps due to their tendencies t oward excessive fracture and wear. The glass fillers in composites provide only limited reinforcement because of the brittleness and low strength of g lass. The aim of the present study was to reinforce dental resins with cera mic single-crystalline whiskers of elongated shapes that possess extremely high strength. A novel method was developed that consisted of fusing silica te glass particles onto the surfaces of individual whiskers for a two-fold benefit: (1) to facilitate silanization regardless of whisker composition; and (2) to enhance whisker retention in the matrix by providing rougher whi sker surfaces. Silicon nitride whiskers, with an average diameter of 0.4 mu m and length of 5 mu m, were coated by the fusion of silica particles 0.04 mu m in size to the whisker surface at temperatures ranging from 650 degre es C to 1000 degrees C. The coated whiskers were silanized and manually ble nded with resins by spatulation. Flexural, fracture toughness, and indentat ion tests were carried out for evaluation of the properties of the whisker- reinforced composites in comparison with conventional composites. A two-fol d increase in strength and toughness was achieved in the whisker-reinforced composite, together with a substantially enhanced resistance to contact da mage and microcracking. The highest flexural strength (195 +/- 8 MPa) and f racture toughness (2.1 +/- 0.3 MPa.m(1/2)) occurred in a composite reinforc ed with a whisker-silica mixture at whisker:silica mass ratio of 2:1 fused at 800 degrees C. To conclude, the strength, toughness, and contact damage resistance of dental resin composites can be substantially improved by rein forcement with fillers of ceramic whiskers fused with silica glass particle s.