Purpose: The study compared the probablity of fracture of 4 systems of all-ceramic crowns fabricated on maxillary central incisors. Materials and Methods: The 4 allceramic crown systems were: (1) a glass-infiltrated, sintered alumina system (In-Ceram) fabricated conventionally, (2) the same system with machine-milled alumina cores (CEREC 2), (3) a heat-press, leucite-reinforced glass-ceramic system (IPS Empress), and (4) a high-purity, high-density alumina system (Procera). Ten crowns of each system were fabricated and compressed at 45 degrees at the palatal surface until failure. The data were analyzed with the Weibull method. Results: There were no significant differences in the probability of fracture among the 4 systems studied. Conclusion: The likelihood of fracture of these crown systems on central incisors should be similar.