The Effect of Implant Angulation on the Performance of the Locator R-TX Overdenture Attachments

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Aims and Objectives: To assess the retention of the Locator R-Tx overdenture attachments, supported on two mandibular implants after a simulated fatigue period of 2.8 years, where the two implants are placed at different angulations.

Materials and Methods: Three test models set-ups were constructed. A 2-implant mandibular implant-supported overdenture design was simulated using acrylic resin blocks to support implant replicas (Model PI, Model MD and Model BL). The replicas were set up in the canine regions (22mm interimplant distance) with 3 different angulations. In Model PI the implants were parallel (0° to the vertical axis), in Model MD they were mesiodistally divergent (20° to the vertical axis for each implant) and in Model BL the implants were buccolingually divergent (5° to the vertical axis for each implant). The Locator R-Tx attachment system were tested at all set-ups. A simulated fatigue period of 2.8 years, that equated to 5,000 cycles of insertion and removal of the denture, was used. Retention values for each attachment system at each angulation set-up were measured at baseline, every 500 cycles until 5,000 cycles.

Results: All three test set-ups showed reductions in the retention values of Locator R-Tx system after simulated fatigue testing. The PI had the highest retention values compared with the divergent set-ups over the whole course of the test period. While comparing the retention of the two divergent set-ups, the BL showed higher values. There was a significant drop in retention values at 500 cycles, which is equivalent to 100 days.

Conclusions: Parallel implant placement would appear to offer the best wear characteristic and performance for the Locator R-Tx overdenture system. Bucco-lingual angulation appears to perform better than mesio-distal angulation. This study offers a clinical significance in the surgical planning of mandibular overdenture cases. Moreover, patient should be informed to expect initial loss of retention within the first period of overdenture wear.