The effect of implant angulation on the performance of the locator R-TX overdenture attachments

Background Dental implants allow the provision of attachments to increase the retention and stability of a denture. Implant-supported overdentures result in patients being able to masticate hard and tough food with an increase in their maximum bite forces and no pain compared to conventional dentures. Aim/Hypothesis To assess the retention of the Locator R-TX overdenture system attachments supported on two mandibular implants where two mandibular implants are placed at different angulations (0 degree, 20 degrees mesiodistally and 5 degrees buccolingually) after a simulated fatigue period of 2.8 years. Material and Methods A 2-implant mandibular implant-supported overdenture design was simulated using acrylic resin blocks to support implant replicas (Model 1, Model 2 and Model 3). The replicas were set up in the canine regions (22 mm inter-implant distance) with 3 different angulations. In Model 1 the implants were parallel (0° to the vertical axis), in Model 2 they were mesiodistally divergent (20° to the vertical axis for each implant) and In Model 3 the implants were buccolingually divergent (5° to the vertical axis for each implant). The Locator R-TX attachment systems were tested at all set-ups. A simulated fatigue period of 2.8 years that equated to 5000 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 5000 cycles. Selected Locator R-Tx abutments and nylon inserts were imaged to qualitatively evaluate wear before and after 5000 cycles. Results All three test set-ups showed reductions in the retention values of Locator R-TX system after simulated fatigue testing. The parallel set-up (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-up, the buccolingual angulation (BL) showed a higher values. Preliminary results shows that PI retention through the course of the tests was reduced from 82.02 (±13.6) to 24.64 (±4.41) N. MD divergence retention decreased from 35.56 (±12.37) to 6.47 (±2.92) N. Retention for BL divergence reduced from 51.69 (±13.34) to 9.15 (±4.78) N. Qualitative image analysis showed wear of the inserts increased when the implant were angulated. Conclusions and Clinical Implications 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.