Comparison of two fracture toughness testing methods using a glass-infiltrated and a zirconia dental ceramic

PURPOSE: The objective of this study was to compare the fracture toughness (K(Ic)) obtained from the single edge V-notched beam (SEVNB) and the fractographic analysis (FTA) of a glass-infiltrated and a zirconia ceramic. MATERIALS AND METHODS: For each material, ten bar-shaped specimens were prepared for the SEVNB method (3 mm × 4 mm × 25 mm) and the FTA method (2 mm × 4 mm × 25 mm). The starter V-notch was prepared as the fracture initiating flaw for the SEVNB method. A Vickers indentation load of 49 N was used to create a controlled surface flaw on each FTA specimen. All specimens were loaded to fracture using a universal testing machine at a crosshead speed of 0.5-1 mm/min. The independent-samples t-test was used for the statistical analysis of the K(Ic) values at α=0.05. RESULTS: The mean K(Ic) of zirconia ceramic obtained from SEVNB method (5.4 ± 1.6 MPa·m(1/2)) was comparable to that obtained from FTA method (6.3 ± 1.6 MPa·m(1/2)). The mean K(Ic) of glass-infiltrated ceramic obtained from SEVNB method (4.1 ± 0.6 MPa·m(1/2)) was significantly lower than that obtained from FTA method (5.1 ± 0.7 MPa·m(1/2)). CONCLUSION: The mean K(Ic) of the glass-infiltrated and zirconia ceramics obtained from the SEVNB method were lower than those obtained from FTA method even they were not significantly different for the zirconia material. The differences in the K(Ic) values could be a result of the differences in the characteristics of fracture initiating flaws of these two methods.