Retention loss and wear assessment of three attachment systems for implant retained-mandibular overdentures: An in vitro study

Background: The stud-shaped attachment systems (AS) with different shape designs (ball, cylindrical, conical) and materials (metallic, plastic, or a combination of both) are commonly used to provide better retention and stability in implant-retained mandibular overdentures (IRMO).Purpose: The purpose of the present study was to evaluate and compare the retention loss and the wear (patterns, location, material loss) of three resilient unsplinted AS: a well-established ball attachment system (BAS) and two more recent cylindrical attachment systems (CAS), Locator R-Tx (R) and Novaloc (R). Materials and methods: The implants, their corresponding abutments, the color-coded or position-coded retention devices (RD), the matrix metal housing were incorporated within CAD/CAM resin blocks and cyclically loaded with 19.6 N along the implant axis in a chewing machine to simulate 10,000 insertion-removal cycles (IRC). At cycle 10, 100, 1,000, 5,000, and 10,000, the retention force was measured using a universal testing machine. The wear was qualitatively examined using a binocular magnifier for both systems, and quantitatively assessed from micro-computed tomography acquisitions for CAS. Material loss exceeding 50 mu m was considered significant.Results: The three AS showed different retentive behavior along time. All the Locator R-Tx (R) RD lost more than 50 % of their retention after 10,000 IRC. The retention of the Ball System slightly varied over time, the final retention loss in B-med and B-max groups being lower than 25 % of the initial retention. Wear was located at the tip of their gold RD and at the equator area of their ball abutment. For Locator R-Tx (R), the more retentive the plastic RD, the greater its wear and retention loss. Only Novaloc (R) maintained a stable retention with even a slight tendency to increase and showed a negligible wear. Implant abutments of the CAS showed no significant wear. Conclusion: After 10,000 IRC, corresponding to approximately 5-years clinical use, almost all RD provided retention force over 5 N, which could be sufficient to maintain satisfaction in most of the patients. The retention loss observed most prominently for the Locator R-Tx (R), then for the Ball System, seemed to correlate with the wear observed on their RD. The practitioner may expect less RD maintenance with the Novaloc (R) stable retention overtime.