Accuracy of Selective Laser Melted Bar Retaining Mandibular Implant-Assisted Overdenture: An In Vitro Comparison of Different Impression Materials and Techniques

Abstract

The purpose of this study was to assess the accuracy of the marginal fit of implant overdenture bars fabricated with selective laser melting technology, utilizing polyvinyl siloxane and vinyl siloxane ether impression materials and different impression techniques. Two implants with multi-unit abutments were inserted in a 3D-printed mandibular model and used as a reference model, then duplicated into a stone cast to fabricate custom trays for obtaining impressions with polyvinyl siloxane and vinyl siloxane ether impression materials, using both open and closed-tray techniques. This resulted in a total of 4 groups, each with 8 specimens. The impressions were poured, scanned, and 32 cobalt-chromium bars were fabricated using selective laser melting technology. Each bar was screwed onto one abutment of the reference model, and a standardized digital periapical radiograph of the opposite unscrewed side was taken, this process was repeated to the other abutment. The vertical misfit was measured at three predetermined positions on the unscrewed side, and six values per bar were recorded. The mean gap distance was measured and the data were subjected to statistical analysis, The study found that the open tray technique using the vinyl siloxane ether group had the lowest mean gap distance and the closed tray technique resulted in a higher mean gap distance compared to the open tray technique regardless of the impression material. In Conclusion, the open-tray impression technique using vinyl siloxane ether impression material resulted in a significantly better fit for bar retaining implant overdenture.