Strength, fracture toughness and microstructure of a selection of all-ceramic materials. Part II. Zirconia-based dental ceramics

Objective: The present study is the second part of an investigation of strength, fracture toughness and microstructure of nine all-ceramic materials. In the present study, DC Zirkon, an experimental yttria partially stabilized zirconia, In-Ceram Zirconia slip and In-Ceram Zirconia dry-pressed were compared. Methods: Strength was appraised on ten bar-shaped specimens for each material (20×4×1.2 mm) with the three-point bending method. The fracture toughness (Indentation Strength) was measured on twenty specimens (20×4×2 mm) for each ceramic. The volume fraction of each phase, the dimensions and shapes of the grains and the crack pattern were investigated with SEM. Phase transformation was investigated with X-ray diffraction. Data were compared with an ANOVA and Sheffé post hoc test (p=0.05). Results: Means of strength (MPa) and fracture toughness (MPa m1/2) values and their standard deviation were: In-Ceram Zirconia dry-pressed 476 (50)1, 4.9 (0.36)1; In-Ceram Zirconia slip 630 (58)2, 4.8 (0.50)1; the experimental yttria partially stabilized zirconia 680 (130)2, 5.5 (0.34)2; DC-Zirkon 840 (140)3, 7.4 (0.62)3. Values with the same superscript number showed no significant statistical difference. Microscope investigation and X-ray diffraction revealed the important role played by the tetragonal to monoclinic phase transformation and by the relationship between the glassy matrix and the crystalline phase in the strengthening and toughening mechanisms of these ceramics. Significance: the zirconia-based dental ceramics are stronger and tougher materials than the conventional glass-ceramics. Better properties can have positive influence on the clinical performance of all-ceramic restorations.