Effects of aging procedures on the topographic surface, structural stability, and mechanical strength of a ZrO2-based dental ceramic

Dent Mater. 2014 Dec;30(12):e396-404. doi: 10.1016/j.dental.2014.08.380. Epub 2014 Sep 22.

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).

Significance: 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.

Keywords: Flexural strength; Phase transformation; Yttria-stabilized tetragonal zirconia.

Publication types

  • Comparative Study

MeSH terms

  • Algorithms
  • Ceramics / chemistry*
  • Crystallography
  • Dental Materials / chemistry*
  • Imaging, Three-Dimensional / methods
  • Materials Testing
  • Pliability
  • Random Allocation
  • Stress, Mechanical
  • Surface Properties
  • Temperature
  • Time Factors
  • Water / chemistry
  • X-Ray Diffraction
  • Yttrium / chemistry*
  • Zirconium / chemistry*

Substances

  • Dental Materials
  • yttria stabilized tetragonal zirconia
  • Water
  • Yttrium
  • Zirconium