Objectives: Due to the reported outstanding mechanical properties and excellent biocompatibility of yttria-stabilized tetragonal zirconia (Y-TZP), it is being offered as a core material to fabricate all ceramic restorations. While engineering literature contains material strength data several methods exist of producing Zirconia for use in dental applications. This study compared material strength of dental use Zirconia produced by 2 separate methods.

Methods: Five specimens each were fabricated in discs with a thickness of 1.5 mm and 2.0 mm and radius of 12.0 mm from DC-Zirkon® used by DCS “Smart-Fit” Cad-Cam system. Ten specimens of Procera®AllZirkon (Nobel Biocare) for their core material were fabricated in discs of 1.2 mm thickness and a radius of 13 mm. All samples were loaded to fracture using a biaxial flexural strength test fixture in an Instron with a cross-head speed of 0.5 mm/min. The radius of the supporting circle and loading area was kept constant. Using the formula S=-0.2387P (X-Y)/d^2, (ISO 6872:1995  8.3.2.4) the flexural strength was calculated from the values of the total load causing fracture, the dimensions of the discs and the dimensions of the biaxial flexural strength test fixture.

Results: 1.5 mm DC-Zirkon® gave a mean load causing fracture of 1232 N; 2.0 mm DC-Zirkon® gave a mean load causing fracture of 2450 N; 1.2 mm Procera® AllZirkon gave a mean load causing fracture of 1068 N. After analyizing the data for material thickness, the flexural strength of Procera® AllZirkon was 1158 MPa and DC-Zirkon® was 927 MPa. The Fisher's PLSD test exhibited a statistically significant difference between the two groups.

Conclusions: Procera® AllZirkon demonstrated a higher flexural strength when compared to DC-Zirkon®.

Supported by NobelBiocare/ University of Michigan Center for Excellence

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