Comparison of the Passivity between CAD/CAM Implant Frameworks and Three Different Conventional Techniques Before and After Applying Veneering Porcelain

Background: The passivity of the fit may be at risk during the casting as well as the firing of the veneering ceramic. In this study, the comparison of the passivity between computer-aided design/computer-assisted manufacturing (CAD/CAM) implant frameworks and three different conventional techniques before and after applying veneering porcelain was investigated. Methods: In this laboratory cross-sectional study, four groups (n=6) of 3-unit screw-retained implant-supported denture prostheses (ISDPs) were fabricated on a master model with 2 implants. The study groups were as follows: conventional casting with Ni-Cr alloy (group 1), casting with Ni-Cr alloy followed by sectioning and soldering the samples (group 2), double casting with Ni-Cr framework (group 3), and using CAD/CAM-fabricated framework (group 4). All frameworks received porcelain veneer. The one-screw test was performed before and after veneering to measure the vertical misfit at the abutment-framework interface using a stereomicroscope. The mean vertical misfit values were determined at the buccal, lingual, and proximal aspects. The data were analyzed using the Kruskal-Wallis and post hoc tests (α=0.05). Results: The accuracy of the fit varied significantly before and after veneering among the study groups (P<0.001). Frameworks prepared with CAD/CAM showed lower mean marginal misfit values compared to the other fabrication methods (P<0.001). Conclusions: Firing the veneering porcelain attached to a screw-retained ISDP may have an adverse effect on the accuracy of the fit. Soft non-pre-sintered CAD/CAM frameworks had better passivity compared to other three conventional methods applied.