Purpose: The study compared the flexural strength of In-Ceram alumina and In-Ceram zirconia systems. The probability of failure of the two glass-infiltrated ceramic core materials was analyzed with and without lamination with Vitadur- porcelain. Materials and Methods: Ten uniform beams of core materials as well as 10 beams of laminated core materials were fabricated for In-Ceram alumina and In-Ceram zirconia. The samples were subjected to three-point bending tests. Flexural strength for both ceramic core materials was determined with and without their porcelain laminations. The strength data were
analyzed using the Weibull method. Modes of failure for both systems were determined using scanning electron micrography. Results: The strength of the In-Ceram zirconia system was significantly higher than In-Ceram alumina when comparing their core materials with and without porcelain lamination. The failure mode for both systems was predominantly transgranular fracture of alumina platelets. Conclusion: In-Ceram zirconia demonstrated higher flexural strength than In-Ceram alumina. Int J Prosthodont 2002;15:183–188.