Axial Displacement in Cement-Retained Prostheses with Different Implant-Abutment Connections

Purpose: The purpose of this study was to evaluate axial displacement in cement-retained prostheses using computer-aided design/computer-aided manufacturing (CAD/CAM) abutments with three different types of implant-abutment connections. Materials and Methods: CAD/CAM abutments made with two types of titanium blocks (made by the same manufacturer as the implant manufacturer and by a manufacturer with a patent for CAD/CAM abutment fabrication) were connected with three types of implant connections: external, internal butt, and internal conical connection. Titanium custom abutments and zirconia prostheses were fabricated using the CAD/CAM system for each specimen. The geometries and surface morphologies of CAD/CAM abutments and ready-made abutments were comparatively evaluated using scanning electron microscopy. Cemented prostheses on abutments were mounted on a universal testing machine and subjected to 250-N sine wave cyclic loads. Cumulative axial displacement was measured at 3, 10, 100, and 106 loading cycles and analyzed by repeated measures analysis of variance (ANOVA). Results: Surface geometries and morphologies of CAD/ CAM abutments varied by the implant-abutment connections and manufacturers of the titanium block. The internal conical connection exhibited the greatest axial displacement, while the external connection showed the lowest axial displacement. The CAD/CAM abutment made with a compatible titanium block exhibited a greater axial displacement than that exhibited by the abutment fabricated using a titanium block made by the implant manufacturer. Conclusion: In implant connections with a vertical stop, axial displacement occurred primarily in the early loading period and was self-limited. However, long-term axial displacement can occur with internal conical connection implants. Therefore, in internal conical connection implants, axial displacement should be managed more carefully using a provisional restoration, with consideration of the abutment fabrication method. Keywords: axial displacement, CAD/CAM abutment, cement-retained prosthesis, cyclic loading, implant-supported dental prosthesis, internal conical connection