Objective: In this in vitro study, the strength of several core and post-and-core systems was compared. A second aim was to compare the strength of posts and cores on root-filled teeth with that of cores on vital teeth. The failure modes of the core and post-and-core systems were also studied. Method and materials: For root-filled teeth, Composipost carbon fiber dowels and gold alloy posts and cores were tested. For vital teeth, glass-ionomer cement with threaded parapulpal retention pins, resin composite with threaded parapulpal retention pins, and gold alloy with parallel parapulpal pins were tested. Specimens were tested in a Zwick universal material-testing machine. Results: A significant variation in strength was found among core systems of cast gold, resin composite, and glass-ionomer cement constructed on vital teeth. The strength of the systems constructed on root-filled teeth did not vary significantly. The mode of failure varied, depending on the core or post-and-core material. Conclusion: Composipost posts and cores and cast gold posts and cores were equivalent in strength and did not vary significantly from gold cores constructed on vital teeth. The low strength values obtained for glass-ionomer cement in combination with threaded retention pins makes this combination a poor choice for core buildup.