In Vitro Comparison of the Retentive Properties of Ball and Locator Attachments for Implant Overdentures

Purpose: To compare the retentive properties of ball and locator attachments during 5,000 insertionseparation cycles, corresponding to approximately 4.5 years of clinical use. Materials and Methods: Four dental implants (diameter, 3.8 mm; length, 12 mm) were inserted into the prepared beds of two polyethylene blocks. Twenty acrylic prosthetic components were fabricated and connected to the ball and locator abutments. Tensile force was applied to the prosthetic components until the attachments were separated from the abutments. All samples were subjected to 5,000 insertion-separation cycles. Retention forces were measured after 10, 100, 200, 300, 400, 500, 1,000, 1,500, 2,000, 3,000, 4,000, and 5,000 insertion-separation cycles. Additionally, the wear of the attachments was measured using scanning electron microscopy. Data were analyzed to determine statistical equivalence among the two different attachments using the Student t test procedure and the Mann-Whitney U test procedure (α = .05). Results: Ball attachments showed significant retention loss after 100, 200, 400, 500, 1,500, and 4,000 cycles, and the locator attachments showed significant retention loss after 100, 200, 300, 500, and 3,000 cycles as compared with the previous cycle (P .05). Retention loss after 5,000 cycles was detected significantly more often for ball attachments than for locator attachments (P = .049). No significant difference was detected between the retention losses of the two attachment systems during the other cycles as compared with the initial retention values (P > .05). No significant difference was detected between the wear on the two attachment systems after 5,000 cycles (P > .05). Conclusion: Both attachment systems showed decreased retentive forces after 5,000 insertion-separation cycles. However, after 5,000 insertion-separation cycles, locator attachments showed better retentive properties than ball attachments. Keywords: edentulous mandible, implant, impression, overdenture