The aim of this study was to survey the fracture toughness values when three different reinforcing particles (Al2O3 whisker, glass fiber and wollastonite) were admixed as reinforcing fillers to pre-polymerized two provisional resin materials. In order to improve the mechanical properties, different ratios of nanopowder Al2O3 whisker, floccular E-glass fiber and wollastonite were separately admixed with prepolimerized acrylic resin beads prior to mixing with the monomer liquid. Polymethylinetacrylate (PMMA) and polyethylinetacrylate (PEMA) were used as resin matrices. All samples were tested for fracture toughness. The results were subjected to ANOVA and Tukey's test. All test materials showed a statistically significant increase in K-Ic after reinforcement with three reinforcement materials when compared to the control groups (p < 0.05). The results showed that all of the fillers had effect on increasing fracture toughness (K,,). All reinforced specimens showed better fracture toughness values than unreinforced resins. Specimens reinforced with floccular glass fiber showed the highest K-Ic values, followed by wollastonite and Al2O3 whisker. The use of fillers is an effective method to increase the fracture toughness of provisional restoration resins. The use of floccular glass fiber and wollastonite is promising for the reinforcement of provisional materials. (c) 2006 Elsevier Ltd. All rights reserved.