Investigation of retentive force reduction and wear of the locator attachment system with different implant angulations.

PURPOSE: To evaluate the effect of cyclic disengagement on the retentive force and wear patterns of pairs of three Locator inserts (blue, pink, and clear) in vitro. MATERIALS AND METHODS: Implant analogs (Astra Tech) were positioned into aluminum blocks parallel to each other and perpendicular to the horizontal plane, with one analog angulated mesially by 10 degrees (0/10), or with two implant analogs each angulated mesially by 5 degrees (5/5). Ninety Locator attachments, in 15 pairs of each standard retention strength (blue, pink, and clear), underwent 2,500 cycles of testing, lubricated with artificial saliva. Data were analyzed after 6, 12, and 18 months of simulated clinical use (720, 1,440, or 2,160 cycles). The wear patterns of the Locator inserts were examined before and after the cyclic dislodgments using scanning electron microscopy. RESULTS: There were significant differences in retentive force between clear, blue, and pink inserts at baseline, with the clear insert being the most retentive in the 0/10 model. The lowest percentage reduction in retentive force from baseline to 2,160 cycles was the pink insert in the 0/10 model, and the highest was the blue insert in the 5/5 angled model. CONCLUSION: A rapid decrease in retentive force was observed in all three models after 720 cycles for all three inserts. The most retentive combination was the clear insert in the 0/10 model, and the least retentive was the blue insert in the 0/10 model. After 2,160 cycles, there was a significant reduction in retentive force of 59% to 70%. However, the values of retention were still higher than those claimed by the manufacturer.