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Objective: To outline a procedure to determine the fracture toughness of direct resin composites failing from “natural” flaws. Methodology: Tensile (hour glass) tests (n = 30) of a conventional hybrid dental composite (Tetric EvoCeram, Ivoclar Vivadent) were fabricated and fractured in uniaxial tension loaded at a crosshead speed of 1 mm/min (≥ 10 MPa/s). The fracture toughness of the material was then calculated using the stress at failure and measurement of the crack size from fractographic analysis using SEM. Hardness (H) measurements were taken using a Vickers pyramidal diamond indenter. Elastic modulus (E) was calculated from the E/H ratio using a Knoop indenter. Results: The values for fracture toughness found were similar to other Bis-GMA based dental composites 0.5 ±0.2 MPa . The Vickers Hardness was 509 ± 27 MPa and the Knoop Hardness was 495 ± 14 MPa using 0.5 kg/30 s, while the elastic modulus was 9.5 ±1.4 GPa. Conclusion: The differences found in fracture toughness between this study and previous published studies are most likely due to variation in technique and material. Quantitative fractographic analysis offers a different method to evaluate the toughness of direct resin composites.

TOUGHNESS MEASUREMENT IN DIRECT RESIN COMPOSITES USING QUANTITATIVE FRACTOGRAPHIC ANALYSIS