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Statement of Problem: Resin composites are a common type of tooth coloured restorative materials. These materials are brittle and their major shortcomings are sensitivity to flaws and defects, low tensile strength, and susceptibility to catastrophic failure.The role of home bleaching agents on the fracture toughness of resin composites using four-point bending test is scanty. Objectives: To compare the fracture toughness (KIc) of resin composites on a fourpoint bending test and to assess the effect of distilled water and a home bleaching agent on the resistance of the materials to fracture. Materials and Methods: seventy-two bar-shaped specimens were prepared from three materials: Rok (SDI), Estelite (Tokuyama), and Vit-l-escence (Ultradent) and divided into three groups. Two groups were assigned as “control” and conditioned in distilled water at 37oC for 24 hours or 21 days, respectively. The specimens in the third group (treatment) were stored in distilled water for 21 days and bleached using Polanight (SDI) for 2 hours daily. For each material, a total of 24 disc-shaped specimens were prepared and after each time interval loaded in a four-point bending test using a universal testing machine with a crosshead speed of 0.5 mm/m. The maximum load to specimen failure was recorded and the KIc was calculated. Results: Statistical analysis using two-way ANOVA showed a significant relationship between materials and treatment (P

Background: Resin-based cements are brittle materials and the major shortcomings of these materials are manifested in their sensitivity to flaws and defects. Although various mechanical properties of resin luting cements have been described, few fracture toughness test data for resin-based luting cements using the short rod design have been published. Methods: Specimens were prepared from five resin luting cements. For each material a total of 36 disc-shaped specimens were prepared using a custom-made mould. Specimens were randomly divided into six groups of six, immersed in two solutions: distilled water and 0.01 mol/L lactic acid at 37 °C for 24 hours, 1 month or 3 months. The specimens were loaded using a universal testing machine. The maximum load at specimen failure was recorded and the KIc (MPa. M 0.5) was calculated. Results: There was a relationship between material, storage solution and time (p < 0.05). Nexus 3 showed the highest KIc followed by Panavia F, Calibra, Smart Cem2 and seT. Conclusions: The fracture toughness of the resin luting cements was affected by both time and storage solution. Comparable fracture toughness of conventional resin cement and self-adhesive resin cements was observed. [ABSTRACT FROM AUTHOR]