Retentiveness of two attachment systems for implant overdentures

The stability and success of implant overdentures depend on the retentiveness and durability of their attachment system. Design features have been related to attachment performance and can affect retentiveness. Objectives: The purpose of this study was to compare the in vitro resistance to dislodgement provided by a cylindrical shape attachment to a traditional ball attachment system. Methods: Six cylindrical attachments with metal caps and white or pink nylon inserts matrices (Locator, Zest Anchor CA) were compared to six ball type attachments with gold female matrices (Retentive Anchor, Straumann AG) as control. A customized portable device was designed to record the maximal tensile forces necessary to remove the attachment abutments from their correspondent matrices. The abutments were screwed into implant analogues and the matrices were embedded in a denture replica base. The measurement was repeated 5 times per specimen, at the baseline and after 30, 300, 600, 1200, 1500, 1800, 2100 insertion/removal cycles. Data were analyzed using Kruskall-Wallis and Dunn's tests (alpha=0.05). Results: Mean peak forces (mean±sd), in Newtons, at the baseline and at 30, 300 and 2100 cycles were, respectively 30.1+/-6.88, 25.42+/-4.13, 21.55+/-0.87, 19.15+/-1.37 for the ball attachments; 68.83+/-11.19, 46.05+/-3.83, 34.74+/-4.39, 23.45+/-4.44 for the cylindrical attachments with white inserts; and 39.33+/-8.03, 30.66+/-8.01, 21.47+/-5.51, 17+/-2.28 for the cylindrical attachments with pink inserts. At baseline, the cylindrical attachments with white or pink inserts presented significantly higher retentiveness than the ball attachments (p<0.05). Loss of initial retention varied between 21-33% after 30 cycles and 37-67% after 2100 cycles. Conclusion: Although the initial values of retention for the cylindrical attachments with white or pink inserts were significantly higher than for the ball attachments no statistical differences were found after one year of simulated wear. Further investigation on the Locator attachment retentiveness should be carried out in the in vivo environment.