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 x 4 x 1.2 mm) with the three-point bending method. The fracture toughness (Indentation Strength) was measured on twenty specimens (20 x 4 x 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 m(1/2)) 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.


CONCLUSIONS
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.
Guazzato
Massimiliano
M
Biomaterials Science Research Unit, Faculty of Dentistry, University of Sydney, United Dental Hospital, 2 Chalmers Street, Surry Hills, NSW, Australia 2010. mgua2483@mail.usyd.edu.au
Albakry
Mohammad
M
Ringer
Simon P
SP
Swain
Michael V
MV
D000704:Analysis of Variance; D018360:Crystallography, X-Ray; D003776:Dental Porcelain / Q000737:chemistry; D003799:Dental Stress Analysis; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D044367:Phase Transition; D018583:Pliability; D016062:Porosity; D018709:Statistics, Nonparametric; D013718:Tensile Strength; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
C485633:In-Ceram Zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide; C091417:yttria