title: Effects of aging procedures on the topographic surface, structural stability, and mechanical strength of a ZrO2-based dental ceramic.
abstract: OBJECTIVE
  To determine the effects of different aging methods on the degradation and flexural strength of yttria-stabilized tetragonal zirconia (Y-TZP) METHODS: Sixty disc-shaped specimens (∅, 12mm; thickness, 1.6mm) of zirconia (Vita InCeram 2000 YZ Cubes, VITA Zahnfabrik) were prepared (ISO 6872) and randomly divided into five groups, according to the aging procedures (n=10): (C) control; (M) mechanical cycling (15,000,000 cycles/3.8Hz/200N); (T) thermal cycling (6,000 cycles/5-55°C/30s); (TM) thermomechanical cycling (1,200,000 cycles/3.8Hz/200N with temperature range from 5°C to 55°C for 60s each); (AUT) 12h in autoclave at 134°C/2bars; and (STO) storage in distilled water (37°C/400 days). After the aging procedures, the monoclinic phase percentages were evaluated by X-ray diffraction (XRD), and topographic surface analysis was performed by 3D profilometry. The specimens were then subjected to biaxial flexure testing (1mm/min, load 100kgf, in water). The biaxial flexural strength data (MPa) were analyzed by 1-way ANOVA and Tukey's test (α=0.05). The data for monoclinic phase percentage and profilometry (Ra) were analyzed by Kruskal-Wallis and Dunn's tests.
  
  
  RESULTS
  ANOVA revealed that flexural strength was affected by the aging procedures (p=0.002). The M (781.6MPa) and TM (771.3MPa) groups presented lower values of flexural strength than did C (955MPa), AUT (955.8MPa), T (960.8MPa) and STO (910.4MPa). The monoclinic phase percentage was significantly higher only for STO (12.22%) and AUT (29.97%) when compared with that of the control group (Kruskal-Wallis test, p=0.004). In addition, the surface roughnesses were similar among the groups (p=0.165).
  
  
  CONCLUSIONS
  Water storage for 400 days and autoclave aging procedures induced higher phase transformation from tetragonal to monoclinic; however, they did not affect the flexural strength of Y-TZP ceramic, which decreased only after mechanical and thermomechanical cycling.
authors.affiliation: 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.
authors.forename: Caroline
authors.initials: C
authors.lastname: Cotes
authors.affiliation: 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.
authors.forename: Anelyse
authors.initials: A
authors.lastname: Arata
authors.affiliation: 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.
authors.forename: Renata M
authors.initials: RM
authors.lastname: Melo
authors.affiliation: 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.
authors.forename: Marco A
authors.initials: MA
authors.lastname: Bottino
authors.affiliation: National Institute of Spatial Researchs-INPE/LAS, São José dos Campos, São Paulo, Brazil.
authors.forename: João P B
authors.initials: JP
authors.lastname: Machado
authors.affiliation: Department of Dentistry, Prosthodontics Unit, Federal University of Rio Grande do Norte (UFRN), Natal/RN, Brazil. Electronic address: rodrigoothavio@gmail.com.
authors.forename: Rodrigo O A
authors.initials: RO
authors.lastname: Souza
mesh_terms: D000465:Algorithms; D002516:Ceramics / Q000737:chemistry*; D003461:Crystallography; D003764:Dental Materials / Q000737:chemistry*; D021621:Imaging, Three-Dimensional / Q000379:methods; D008422:Materials Testing; D018583:Pliability; D011897:Random Allocation; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D014867:Water; D015019:Yttrium; D015040:Zirconium
keywords: Flexural strength; Phase transformation; Yttria-stabilized tetragonal zirconia