Fracture toughness of aged dental composites in combined mode I and mode II loading

Resin-based laboratory dental composites for prosthetic restorations have b een developed in the past years as a cost-effective alternative to conventi onal porcelain-fused-to-metal or full ceramic restorations. The fracture to ughness at different stress states (K-Ic, K-IIc, and mixed-modes K-I, K-II) was assessed for three laboratory dental composite resins used for prosthe tic restorations that were aged up to 12 months in a food simulating fluid (10% ethanol) at 37 degrees C. The materials were mainly di- methacrylate b ased resins reinforced with submicron glass filler particles. The Brazilian disk test was used on precracked chevron-notched specimens, and different stress states were obtained by angulating the precracked chevron notch rela tive to the diametral compressive loading direction. The stress intensity f actors were calculated using Atkinson's et al.'s relation. For all three ma terials, mode I fracture toughness values ranged between 0.48-0.64 MPa . m( 0.5) and mode II values ranged between 0.93-1.2 MPa . m(0.5). Overall, agin g time and storage media had little effect on toughness. Considering the in herently low toughness of these restorative materials, their use should be limited to low stress masticatory areas. (C) 2000 John Wiley & Sons, Inc.