The fracture strengths of amalgam and composite resin cores retained by three types of intradentinal retentive features were compared with the fracture strength of cores retained by four self-threaded retentive pins. Composite resin cores had significantly greater resistance to fracture than amalgam cores with any of the retentive features. The fracture strength of amalgam cores retained by retentive pins was comparable to that of amalgam cores retained by a post with a countersink, but significantly higher than the strength of those retained by slots or channels. The fracture strength of composite resin cores retained by retentive pins was significantly higher than that of composite resin cores retained by any of the alternative intradentinal retentive features.