AbstractThe retention in root canals of Flexi‐Posts, Para‐Posts and Brasseler/Vlock‐Posts was measured using tensile and compressive/shear forces. Forty‐two extracted maxillary anterior teeth were embedded in self‐curing acrylic resin and treated endodontically. Each root canal was prepared with the appropriate matching drills for the post‐core system chosen. Each post‐core was cemented in the canal with zinc phosphate cement. A tensile force was applied along the long axis of each tooth and the force needed to dislodge the post‐core was recorded. There was no difference in retention between the small diameter posts, but the difference between the medium and the large diameter posts, however, was significant. In the medium diameter post group, the Flexi‐Post was approximately twice as retentive as the other two post‐core systems evaluated. In the second series of tests compressive/shear force was applied at an angle of 130 degrees to the long axis of the tooth. The retention difference between the small diameter posts was found to be statistically significant, Flexi‐Posts being more retentive than Par