COMPARISON OF RETENTION AND RELEASE PERIODS FOR IMPLANT OVERDENTURE ATTACHMENTS

The aim of this study mas to compare tile retention and release period s of the Nobel Biocare bar and clip (NBC), Nobel Biocare ball (NB), Ze st anchor (ZA), Zest magnet (ZM), and Sterngold ERA (SE) attachments o n art implant-retained overdenture model. The attachments were tested using two permanently placed Branemark implants on a test model that w as attached to an Instron machine (cross-head speed 50.8 mm/minute). E ach 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 simulating function vertical and oblique, Eight tests were done in two directions with three sampl es of each attachment. The dislodging forces generated measurements of the peak load, break load, and displacement at peak load and break lo ad. Release periods were calculated using displacements between the pe ak load and break load and the cross-head speed. Results showed the NB C to be significantly most retentive for the break load when subjected to vertical and oblique forces with mean values and standard deviatio ns of 2104.5 +/- 506.7 g and 1958.1 +/- 165.4 g, respectively. Next mo st retentive was the SE, followed by the ZA and NE. The ZM was signifi cantly 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 fast est release period for vertical and oblique forces (1.86 x 10(-3) and 1.35 x 10(-4) minutes). The ZM significantly had the slowest release p eriod for those forces (3.02 x 10(-2) and 2.35 x 10(-2) minutes). The data suggested that the NBC could be selected when a high degree of re tention and fast release period are desired. The next most retentive w as the SE;ZM was the least retentive and had the slowest release perio d.