226 Fracture Strength of Machinable Ceramic-Zirconia Discs: Effect of Thickness Ratio

Thursday, March 22, 2012: 2 p.m. - 3:15 p.m.
Presentation Type: Poster Session
M.H. ZAHRAN1, O. EL-MOWAFY1, A. JOKSTAD2, L. TAM1, and A. RIZKALLA3, 1Faculty of Dentistry, University of Toronto, Toronto, ON, Canada, 2Professor and Head, Prosthodontics, University of Toronto Faculty of Dentistry, Toronto, ON, Canada, 3Div. of Biomaterials Science, University of Western Ontario -, London, ON, Canada

Objective: to determine effect of varying total and core thicknesses on the fracture strength of bilayered zirconia-machinable ceramic samples fabricated using Rapid Layering technique (Vita Zahnfabrik, Bad Sackingen, Germany). Methods: Forty zirconia rectangular specimens (e.max ZirCad, Ivoclar Vivadent, Schaan, Liechtenstein) were prepared in two thicknesses (0.6 and 1.0mm). Forty machinable ceramic rectangular specimens (Vita Mark II, Vita) were prepared in four different thicknesses (0.6, 0.9, 1.0 and 1.4mm) and used as veneering layers. The veneering layers were cemented to the zirconia discs to produce 4 groups (n=10) as shown in (Table1). Twenty zirconia specimens with two thicknesses (1.5 and 2.0mm) were used as controls. All specimens were cemented to epoxy resin blocks (5mm in thickness, Viade Products Inc., Camarillo, CA). Specimens were loaded at the center of the monolithic samples or the center of the veneer layer of the bilayered samples using an 8mm tungsten carbide ball in a hydraulic-driven universal testing machine (Instron 8501; Instron, Canton, MA) at cross-head speed of 0.5mm/min and fracture loads (N) were recorded. Fracture load data was analyzed using Factorial ANOVA to evaluate the effect of core and total thicknesses. One-way ANOVA, followed by Tukey's test, was used to compare the fracture loads of all groups (including controls). Results: The fracture loads of the study groups are reported in Table1.  Factorial ANOVA revealed a statistically-significant effect of the core and total thicknesses on the fracture load (P<0.05). One-way ANOVA revealed a statistically-significant difference among the groups (P<0.05). The fracture strength of the monolithic controls was significantly higher than the bilayered samples with similar total thickness. Conclusion:  The fracture strength of the bilayered ceramic-zirconia discs is affected by both total specimen thickness and core thickness.

Acknowledgements: Ivoclar/Vivadent, Kuraray, and Select Dental Lab.


Group *

Total thickness (mm)

Core : veneer thickness (mm)

Fracture load (N)

Mean (SD)

1 A


0.6 :  0.9

711 (127)

2 B


1.0 :  0.5

1039 (301)

3 C


Monolithic Zirconia

1431 (178)

4 A, B


0.6 :  1.4

935 (116)

5 C


1.0 :  1.0

1430 (177)



Monolithic Zirconia

2272  (206)

*Groups with similar letters showed no statistically significant difference (Tukey's test, p>0.05).

This abstract is based on research that was funded entirely or partially by an outside source: University of Toronto, Faculty of Dentistry Research Committee Grant and Education and Research Foundation of Prosthodontics

Keywords: Biomaterials, CAD/CAM, Cements, Ceramics and Zirconia
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