Fatigue behavior and surface characterization of a Y-TZP after laboratory grinding and regeneration firing

Abstract

This study evaluated the effect of grinding and regeneration firing on the flexural fatigue limit and surface characterization of Lava™ Y-TZP ceramic. Forty bar-shaped specimens with 20 × 4.0 × 1.2 mm constituted the as-sintered group (AS = control group), and 80 specimens with 20 × 4.0 × 1.5 mm were ground with cylindrical laboratory stone under water-cooling (WG) or in a dry condition (G) to reach 1.2 mm in thickness. Half of specimens were submitted to regeneration firing (1000 °C, 30 min), forming the groups AS/R, WG/R and G/R. Fatigue limit (500,000 cycles, 10 Hz) was determined by staircase method in a 4-point flexural fixture. Data were analyzed by 2-way ANOVA and Tukey HSD tests (α = 0.05). The surface topography (n = 3) and fracture area (n = 3) were evaluated by SEM. Samples were also analyzed by Rietveld refinement from X-ray diffraction data. ANOVA revealed significant differences (P < .001) for grinding protocol, regeneration firing and their interaction. In the groups not submitted to regeneration firing, the mean flexural fatigue limit of WG was higher (P < .05) than that of G and AS, with no statistical difference between each other (P > .05). After regeneration firing the inequality WG>AS>G (P < .05) was observed. The regeneration firing increased the fatigue limit of AS group and decreased those of G and WG groups (P < .05). Grinding protocols created evident grooves on zirconia surface. Failures initiated on tensile side of all specimens. The percentages (wt%) of monoclinic phase before cyclic loading were: AS (7.4), AS/R (6.5), G (2.8), G/R (0.0), WG (4.4), WG/R (0.0); and after cyclic loading: AS (8.6), AS/R (1.2), G (2.4), G/R (5.7), WG (6.3), WG/R (0.0). Wet grinding did not compromise the fatigue limit of zirconia, increasing its mechanical strength. Regeneration firing reduced the fatigue limit of ground samples, despite reducing the amount of monoclinic phase in all experimental conditions.

Effect of surface finishing and polishing procedures on color properties and translucency of monolithic zirconia restorations at varying thickness

“…However, the term “partially” stabilized zirconia (PSZ) refers to lower concentrations of Y2O3 between 4 and 6 mol%. In order to achieve high translucency of yttria‐stabilized polycrystal zirconia (Y‐TZP), the aluminum content is lowered and the yttria content is increased in order to minimize the low‐temperature degradation of the material 3‐7 …”

Surface properties and flexural strength of a monolithic zirconia submitted to grinding and regenerative heat treatment

“…After the HT, a total reversal of m→t phase was observed for both the treatment of 900°C/1 h (C9 and G9) and 1000°C/30 min (C10 and G10). This behavior had already been observed for the conventional zirconia, 25,34,35 but not for the monolithic zirconia. It was observed that the heat treatment was able to maintain the direction of the transformation phases m→t→c, converting the monoclinic phase into tetragonal and tetragonal into cubic, returning the material to its initial conformation.…”