Objective: To compare the intrinsic strengths of a variety of commercial medical grade ceramics, including: 3M Lava zirconia, Vita zirconia, Nobel Biocare Procera zirconia and alumina, Norton Prozyr Y-TZP, and CoorsTek alumina. To determine the application strengths of selective dental core ceramics, namely 3M Lava zirconia and Nobel Biocare Procera zirconia. Methods: Five specimens from each brand were used to determine the intrinsic strengths. Specimens with dimensions of 10mmx10mmx1mm were ground and polished to 1 micron finish. The plates were epoxy bonded to polycarbonate substrates. The ceramic/substrate bilayers were loaded at their top surfaces with a WC sphere (r=3.18mm) using an Instron machine at a loading rate of 1mm/min. The critical loads for the fracture were determined and the intrinsic flexural strengths were calculated using an established equation based on fracture mechanics. Two dental ceramics (Lava zirconia and Procera zirconia) of ten specimens each were subject to different surface treatments: as-received CAD/CAM surface and 600-grit diamond grinding. Five specimens from each group were subject to simulated porcelain veneering procedures. Specimens were cemented onto Z100 blocks, representing the crown/dentin structure. Application strengths were again determined using the indentation technique described above. Results: The intrinsic strengths (n=5, Mean±SD, MPa) of the ceramics tested are: Vita zirconia (1267±116), Lava zirconia (1475±92), Procera zirconia (1654±152), Prozyr Y-TZP (2486±88), Procera alumina (706±46), and CoorsTek alumina (754±60). The application strengths of as-received surfaces are nearly identical to the intrinsic strengths of polished surfaces. However, 600-grit ground surfaces retain approximately 60% of the intrinsic strength values. Porcelain veneering procedures have minor impact on the materials' application strengths. Conclusions: The zirconia ceramics studied exhibit higher strengths as compared to alumina. The application strengths measured from ceramic/Z100 layered structures are more representative of the ceramic crown strengths on dentin.

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