Fracture toughness and hardness of a new dental ceramic

Objective: The aim of this study was to evaluate the fracture toughness (KC) and hardness (H) of VITAVM7 ceramic (Vita Zahnfabrik, Bad Sackingen, Germany). KC is a conventional fracture mechanics parameter indicating the resistance of a material to crack propagation. H is the material resitance to plastic deformation. Methods: Ten disk specimens of VITAVM7 (9 mm x 2.5 mm) were fabricated according to the manufacturer's instruction and ISO 6872 standard. The specimens were polished through 1200 grit SiC paper followed by 4 µm and 1 µm diamond pastes. Specimens were submitted to an additional firing of 50^oC over the ceramic Tg to minimize the residual stress. All specimens received 3 indentations (1.5 kg for 30 s) in a Vickers microhardness tester (Shimadzu, Japan). The diagonals and radial cracks were measured and the H and KC values were calculated using H=0,5(P/a²) and KC=0,028(E/H)^1/2Ha^1/2(c/a)^-3/2, where P is the applied load, a is the indentation half-diagonal, E is the Young Modulli (58 GPa) and c is the median crack size. The Kc formula was selected according to the c/a ratio. Results: Mean and standard deviation values of H (GPa) and KC (MPa•m^1/2) were as follows: 10,6±0,5 e 0,874±0,09. Conclusion: The H and Kc mean values of VITAVM7 are in agreement with the values of ceramics from same class.