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

ObjectiveTo determine the effects of different aging methods on the degradation and flexural strength of yttria-stabilized tetragonal zirconia (Y-TZP)MethodsSixty disc-shaped specimens (∅, 12 mm; thickness, 1.6 mm) 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/3.8 Hz/200 N); (T) thermal cycling (6,000 cycles/5–55 °C/30 s); (TM) thermomechanical cycling (1,200,000 cycles/3.8 Hz/200 N with temperature range from 5 °C to 55 °C for 60 s each); (AUT) 12 h in autoclave at 134 °C/2 bars; 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 (1 mm/min, load 100 kgf, 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.ResultsANOVA revealed that flexural strength was affected by the aging procedures (p = 0.002). The M (781.6 MPa) and TM (771.3 MPa) groups presented lower values of flexural strength than did C (955 MPa), AUT (955.8 MPa), T (960.8 MPa) and STO (910.4 MPa). 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).SignificanceWater 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.