Objectives: To determine the effect of porcelain thickness and the application of a surface liner (SL) on the flexural strength (σ) of a ceramic system.
Methods: One hundred twenty bar-shaped specimens of yttria-stabilized zirconia-based ceramic were fabricated and randomly divided into two groups according to the application of SL: A - applied; B - not applied. The specimens were further divided according to the porcelain veneer thickness (n=20): 0-0.5mm; 1-1.0mm; 2-2.0mm. All specimens were tested in 3-point bending with the porcelain under tension. The maximum load was recorded at first sign of fracture, the σ was calculated and the mode of failure was determined. Data was statistically analyzed using one-way ANOVA, Tukey (α=0.05) and Weibull distribution.
Results: The SL application had no effect (p=0.723) while the porcelain thickness had a significant effect (p=0.000) on the mean σ values. No significant differences in mean σ values were found with same porcelain thickness. A 0.5-mm thick porcelain layer (groups A0 and B0) showed greater mean σ values than other groups. The Weibull modulus (m) ranged from 6 (groups A1 and B2) to 9 (groups A0, A2 and B0). The predominant mode of failure for all groups was fracture initiation at the porcelain surface propagating to the ceramic interface.
Significance: The porcelain thickness influenced the mean σ values, but the SL had no significant effect on the flexural strength and the mode of failure of the ceramic system examined.
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