Dental Y-TZP Ceramics: Local Fracture Resistance

The behavior of dental Y-TZP zirconia ceramics (in comparison with technical ones) was studied on Rockwell edge chipping the polished rectangular specimen by the EF (edge fracture) method of determining the fracture toughness characteristics. The fracture resistance F_R is defined as the ratio of the fracture load P_f to distance L from the specimen edge to the extreme point on the chip scar. Recording of loads at all the stages of fracture crack development (nucleation, formation, and propagation), in contrast to other methods, provides for evaluating the crack nucleation resistance. The F_R – L relation plotted by the test results is convex and flattens out at L = 0.3 mm. The fracture resistance F_Rp corresponding to this plateau can be regarded as a new mechanical characteristic of Y-TZP zirconia ceramics. The comparison of ceramics by their fracture resistance values was demonstrated to be untrue unless they were obtained with the indentors of identical tip radii. The fracture resistance of different materials shows the most marked distinctions on their chipping with a standard Rockwell indentor, while it is the most accurate one if the characteristic F_Rp is used. The test results did not reveal any essential differences in fracture resistance values for examined dental and technical ceramics.