Retention Evaluation of Implant-Supported Mandibular Overdenture Using Two Different Attachment Systems: An in Vitro Study

Objective: The purpose of this in vitro study was to evaluate the retentive behavior of implant-supported overdenture using two different attachment systems (locator and milled bar-clip attachment system). Methods: Six edentulous mandibular models were fabricated from cold‑cure PMMA; the denture-bearing area of the acrylic resin model was covered by an approximately 1.5 mm thick silicone resilient liner to simulate mucosa. The Study models were divided into three groups: Model A (locator), Model B (milled bar-clip attachment system without extension), and Model C (milled bar-clip attachment system with 1cm extension). However, for each study model, a complete mandibular denture was constructed. Anterior, posterior, and central dislodging forces were measured by digital force gauge at the beginning of the study (Initial retention) and after 540 courses of consecutive pulling and inserting the prosthesis (final retention), which was to simulate six months of overdenture use assuming three daily removals and insertions for oral hygiene practice. Results: There were statistically significant differences in retention between the group models, and milled bar-clips attachment systems revealed the highest retentive capacity. However, after six months of simulated use, there was a significant retention loss; retention of Model B recorded the highest percentage loss of 55.1%, while Model A recorded the most minor retention loss of 24%. Conclusions: The bar and clip attachment system offered higher retentive values than the locator attachment system. However, the retention loss was correlated to the particular attachment system, and the bar–clip attachment systems had the highest percent of retention loss. In contrast, the locator attachments were associated with acceptable retention, simplicity, and minimal retention