The aim of this study was to compare the retention and release periods of the Nobel Biocare bar and clip (MBC), Nobel Biocare ball (NB), Zest anchor (ZA), Zest magnet (ZM), and Sterngold ERA (SE) attachments on an implant-retained overdenture model. The attachments were tested using two permanently placed Branemark implants on a test model that was attached to an Instron machine (cross-head spped 50.8 mm/minute). Each attachment had one part embedded in a denturelike housing, and the other part screwed into the implants. Dislodging tensile forces were applied to the housings in two directions imulating function: vertical and oblique. Eight tests were done in two directions with three samples of each attachment. The dislodging forces generated measurements of the peak load, break load, and displacement at peak load and break load. Release periods were calculated using displacements between th e peak load and the break load and the cross-head speed. Results showed the NBC to be significantly most retentive for the break load when subjected to vertical and oblique forces with mean values and standard deviations of 2104.5 ± 506.7 g and 1958.1 ± 165.4 g, respectively. Next most retentive was the SE, followed by the ZA and NB. The ZM was significantly least retentive (127.8 ± 7.0 g and 143.5 ± 19.7 g). For the release period, results showed the NBC to have significantly the fastest release period for vertical and oblique forces (1.86 x 10 to the negative third power and 7.35 x 10 to the negative fourth power minutes). The ZM significantly had the slowest release period for those forces (3.02 x 10 to the negative second power and 2.35 x 10 to the negative second power minutes). The data suggested that the NBC could be selected when a high degree of retention and fast release period are desired. The next most retnetive was the SE, ZM was the least retentive and had the slowest release period.