Monoclinic phase transformation and mechanical durability of zirconia ceramic after fatigue and autoclave aging.
This study evaluated the influence of two aging procedures on the biaxial flexural strength of yttria-stabilized tetragonal zirconia ceramics.



Disc-shaped zirconia specimens and (ZE: E.max ZirCAD, Ivoclar; ZT: Zirkon Translucent, Zirkonzahn) (N = 80) (∅:12 mm; thickness:1.2 mm, ISO 6872) were prepared and randomly divided into four groups (n = 10 per group) according to the aging procedures: C: Control, no aging; M: mechanical cycling (2 × 106cycles/3.8 Hz/200 N); AUT: Aging in autoclave at 134°C, 2 bar for 24 h; AUT + M: Autoclave aging followed by mechanical cycling. After aging, the transformed monoclinic zirconia (%) were evaluated using X-ray diffraction and surface roughness was measured using atomic force microscopy. The average grain size was measured by scanning electron microscopy and the specimens were submitted to biaxial flexural strength testing (1 mm/min, 1000 kgf in water). Data (MPa) were statistically analyzed using 2-way analysis of variance and Tukey's test (α = 0.05).



Aging procedures significantly affected (p = 0.000) the flexural strength data but the effect of zirconia type was not significant (p = 0.657). AUTZT(936.4 ± 120.9b) and AUT + MZE(867.2 ± 49.3b) groups presented significantly higher values (p < 0.05) of flexural strength than those of the control groups (CZT: 716.5 ± 185.7a; CZE: 779.9 ± 114a) (Tukey's test). The monoclinic phase percentage (%) was higher for AUTZE(71), AUTZT(66), AUT + MZE(71), and AUT + MZM(66) compared to the C groups (ZE:0; ZT:0). Surface roughness (µm) was higher for AUTZE(0.09), AUTZT(0.08), AUT + MZE(0.09 µm), and AUT + MZT(0.09 µm) than those of other groups.



Regardless of the zirconia type, autoclave aging alone or with mechanical aging increased the flexure strength but also induced higher transformation from tetragonal to monoclinic phase in both zirconia materials tested. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1972-1977, 2017.
Department of Restorative Dentistry, Federal University of Juiz de Fora, Juiz de Fora, Brazil.
Yasmine A
YA
Mota
Department of Dental Materials and Prosthodontics, São José dos Campos Dental School, Institute of Science and Technology (UNESP), Universidade Estadual Paulista, São José dos Campos, São Paulo, Brazil.
Caroline
C
Cotes
Department of Dental Materials and Prosthodontics, São José dos Campos Dental School, Institute of Science and Technology (UNESP), Universidade Estadual Paulista, São José dos Campos, São Paulo, Brazil.
Rodrigo F
RF
Carvalho
INPE/LAS, National Institute of Spatial Researchs (NPE/LAS), São José dos Campos, São Paulo, Brazil.
João P B
JPB
Machado
Department of Restorative Dentistry, Federal University of Juiz de Fora, Juiz de Fora, Brazil.
Fabíola P P
FPP
Leite
Department of Dentistry, Prosthodontics Unit, Federal University of Rio Grande do Norte (UFRN), Natal/RN, Brazil.
Rodrigo O A
ROA
Souza
Dental Materials Unit, Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, Dental Materials Unit, Center for Dental and Oral Medicine, University of Zürich, Zürich, Switzerland.
Mutlu
M
Özcan
D002516:Ceramics / Q000737:chemistry*; D006358:Hot Temperature; D011312:Pressure; D013314:Stress, Mechanical; D015040:Zirconium / Q000737:chemistry*
D015040:Zirconium; C028541:zirconium oxide
aging; flexural strength; mechanical cycling; phase transformation; yttria-stabilized tetragonal zirconia