Flexural Strength of Different Yttrium Oxide- Containing Monochrome and Multilayer Partially Stabilized Zirconia at Various Sintering Rates.

Abstract

Purpose: To evaluate the effect of varying sintering rates on the flexural strength (σ) of 3, 4, and 5 mol% yttria (Y)-containing monochrome (Mo) and multilayer (Mu) zirconia.

Materials and methods: In total, 270 specimens (11.2 × 20 × 1.5 mm) were prepared from Mo and Mu 3Y, 4Y, and 5Y zirconia and randomly sintered with regular (RS: 10°C/minute), fast (FS: 35°C/minute), and speed (SS: 70°C/minute) sintering (n = 15/group). Three-point bending test was used to determine σ. ANOVA and Bonferroni test were used to analyze significant differences of σ (α = .05). The microstructure and crystalline-monoclinic (m), tetragonal (t), and cubic (c)-phases were evaluated with a scanning electron microscope (SEM) and X-ray diffraction (XRD).

Results: The σ of zirconia was affected by zirconia type, shade pattern, and sintering rate. Significantly higher σ results were found for 3Y > 4Y > 5Y (P < .05), significantly greater σ was found for Mu > Mo (P < .05), and significant reduction of σ was found upon SS compared to RS and FS (P < .05). However, no significant effect on σ was found for varying sintering rates within each type of zirconia (P > .05). SEM indicated greater grain size in 5Y than in 4Y and 3Y. XRD indicated a higher t phase in 3Y but a higher c phase in 5Y. Mo indicated a higher c phase than Mu.

Conclusions: σ was influenced by Y content (3Y > 4Y > 5Y), shade pattern (Mu > Mo), and sintering rate (RS ≅ FS > SS). Nonetheless, varying sintering rates had no influence on σ for each type of zirconia, suggesting that sintering zirconia with RS and FS will result in higher σ and sintering zirconia at SS will result in acceptable σ for chairside cost-effective restoration.