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® and Novaloc®. 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 µm was considered significant. RESULTS: The three AS showed different retentive behavior along time. All the Locator R-Tx® 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 Bmed and Bmax 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®, the more retentive the plastic RD, the greater its wear and retention loss. Only Novaloc® 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®, 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® stable retention overtime.

Evaluation of Retention, Wear, and Maintenance of Attachment Systems for Single- or Two-Implant-Retained Mandibular Overdentures: A Systematic Review.

Attachment systems (AS) enhance retention and stability by anchoring the overdentures to implants. Since 2002, the McGill consensus statement recommends the 2-implant-retained overdentures as the standard choice for edentulous mandible (2-IRMO). Considering the large number of AS available, it remains difficult for a practitioner to make a reasoned choice. A systematic review was conducted in PubMed/Medline and carried out independently by three authors, on retention, wear, and maintenance of AS used clinically or in vitro specifically for 1- or 2-IRMO. The 45 selected studies include 14 clinical and 31 in vitro studies. The risk of bias was evaluated according to the revised Cochrane risk of bias tool for randomized trials (RoB 2). The initial retention force of the cylindrical system is higher than the ball system. The retention loss, related to the wear of the retention device, is responsible for the most common need of maintenance, requiring activation or replacement. Plastic retention devices wear out faster and more significantly than metal ones, implying a worse time behavior of cylindrical systems, but their maintenance rate is similar. Neither system appears categorically superior. Cylindrical systems provide higher initial retention than ball ones; this advantage reduces over time with wear without affecting their need for maintenance.