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The biaxial flexural strength of Optimal pressable ceramics and IPS Empress pressable ceramics were tested, compared and the microstructures and compositions explored. The materials evaluated were Optimal shaded (Opcs) and unshaded (Opcus) ceramics and IPS Empress shaded (Ems) and unshaded (Emus) ceramics. Twenty-one disc specimens per material were prepared, heat-treated and tested. The piston on three-ball test ASTM F394-78 (1991) was used to test the specimens in a universal testing machine at a crosshead speed of 0.15mm/min. Specimens were viewed in a scanning electron microscope and X-ray diffraction used to determine the phases present. Mean strengths (MPa±SD) were: Ems 120.1±20.5, Emus 135.8±16.0, Opcs 139.1±14.3 and Opcus 138.0±11.5. There was no statistically significant difference between Optimal shaded, Optimal unshaded and Empress unshaded strength …