title: Low-temperature degradation of different zirconia ceramics for dental applications.
abstract: The aim of this investigation was to determine the influence of simulated ageing on the tetragonal-to-monoclinic phase transformation and on the flexural strength of a 3Y-TZP ceramic, compared to alumina toughened zirconia (ATZ) and ceria-stabilized zirconia (12Ce-TZP). Standardized disc specimens of each material were hydrothermally aged in steam at 134°C and 3bar for 0, 16, 32, 64 or 128h. The phase transformation was determined by X-ray diffraction (XRD) and atomic force microscopy. Scanning electron microscopy was performed to estimate the depth of the transformation zone. The flexural strength was investigated in a biaxial flexural test. XRD revealed a significant increase in the monoclinic phase content for 3Y-TZP and ATZ due to ageing, although this increase was less pronounced for ATZ. In contrast, the monoclinic phase content of 12Ce-TZP was not influenced. For 3Y-TZP and ATZ, a transformation zone was found of which the depth linearly correlated with ageing time, while for 12Ce-TZP no transformation zone could be observed. Changes in flexural strength after ageing were heterogeneous: while 3Y-TZP showed a significant decrease in strength - from 1740 to 1169 MPa - with ATZ there was a considerable increase - from 1093 to 1378 MPa. The flexural strength of 12Ce-TZP remained unaffected at the low level of about 500 MPa. These results indicate that both alumina and ceria, as stabilizing oxides, reduce the susceptibility of zirconia to hydrothermal degradation; the alternative use of these oxides may enhance the clinical long-term stability of dental zirconia restorations.
authors.affiliation: Department of Prosthetic Dentistry and Biomedical Materials Science, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany. kohorst.philipp@mh-hannover.de
authors.forename: Philipp
authors.initials: P
authors.lastname: Kohorst
authors.forename: Lothar
authors.initials: L
authors.lastname: Borchers
authors.forename: Jürgen
authors.initials: J
authors.lastname: Strempel
authors.forename: Meike
authors.initials: M
authors.lastname: Stiesch
authors.forename: Thomas
authors.initials: T
authors.lastname: Hassel
authors.forename: Friedrich-Wilhelm
authors.initials: FW
authors.lastname: Bach
authors.forename: Christoph
authors.initials: C
authors.lastname: Hübsch
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D002563:Cerium / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D006358:Hot Temperature; D008422:Materials Testing; D018625:Microscopy, Atomic Force; D013997:Time Factors; D014961:X-Ray Diffraction; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; D002563:Cerium; D015040:Zirconium; C028541:zirconium oxide