J Adv Prosthodont.  2015 Oct;7(5):358-367. 10.4047/jap.2015.7.5.358.

Biaxial flexural strength of bilayered zirconia using various veneering ceramics

• Chantranikul N
• Salimee P

• KMID: 2083878
• DOI: http://doi.org/10.4047/jap.2015.7.5.358

Abstract

PURPOSE
The aim of this study was to evaluate the biaxial flexural strength (BFS) of one zirconia-based ceramic used with various veneering ceramics.
MATERIALS AND METHODS
Zirconia core material (Katana) and five veneering ceramics (Cerabien ZR; CZR, Lava Ceram; LV, Cercon Ceram Kiss; CC, IPS e.max Ceram; EM and VITA VM9; VT) were selected. Using the powder/liquid layering technique, bilayered disk specimens (diameter: 12.50 mm, thickness: 1.50 mm) were prepared to follow ISO standard 6872:2008 into five groups according to veneering ceramics as follows; Katana zirconia veneering with CZR (K/CZR), Katana zirconia veneering with LV (K/LV), Katana zirconia veneering with CC (K/CC), Katana zirconia veneering with EM (K/EM) and Katana zirconia veneering with VT (K/VT). After 20,000 thermocycling, load tests were conducted using a universal testing machine (Instron). The BFS were calculated and analyzed with one-way ANOVA and Tukey HSD (alpha=0.05). The Weibull analysis was performed for reliability of strength. The mode of fracture and fractured surface were observed by SEM.
RESULTS
It showed that K/CC had significantly the highest BFS, followed by K/LV. BFS of K/CZR, K/EM and K/VT were not significantly different from each other, but were significantly lower than the other two groups. Weibull distribution reported the same trend of reliability as the BFS results.
CONCLUSION
From the result of this study, the BFS of the bilayered zirconia/veneer composite did not only depend on the Young's modulus value of the materials. Further studies regarding interfacial strength and sintering factors are necessary to achieve the optimal strength.

Keyword

Flexural strength; Veneering ceramic; Zirconia

MeSH Terms

Ceramics*
Elastic Modulus
Ceramics

Figure

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  Fig. 1 Design of the bilayered zirconia/veneer disk specimen (A) and firing program of Katana zirconia-based on the recommendation of manufacturers (B).

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  Fig. 2 BFS test conducted on bilayered zirconia/veneer specimens using a universal testing machine according to ISO standard 6872:2008.

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  Fig. 3 The formulation of BFS for bilayered disk. *R = equivalent radius of loading, M = maximum bending moment (N), W = work load (N), P = maximum work load (N), n = Poisson's ratio (0.25), A = support circle's radius (5 mm), B = piston's radius (0.75 mm), C = specimen's radius (6.25 mm), d = specimen's thickness (1.50 mm), ta = upper layer's thickness (0.75 mm), tb = lower layer's thickness (0.75 mm), Ea = Young's modulus of upper layer, veneering porcelain, (CZR = 76, LV = 80, CC = 65, EM = 95 and VT = 65.52 GPa), Eb = Young's modulus of lower layer, Katana zirconia core (205 GPa).

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  Fig. 4 Weibull plots of five groups of zirconia/veneer specimens.

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  Fig. 5 Fracture pattern of tested specimen from each study group.

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  Fig. 6 Scanning electron micrographs at fracture surface of tested specimen from each group. Note that the porosities were observed in veneering ceramic especially in CC and LV.

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