Titanium Base-Free Multi-Unit Abutment Connections: A Critical Review of Prosthetic Screw Design, Biomechanical Behavior, and Clinical Performance

Titanium base-free multi-unit abutment (MUA) restorations have been introduced to simplify implant prosthetic workflows by eliminating intermediate titanium bases and bonding interfaces. However, this approach modifies the biomechanical behavior of the prosthesis-abutment-implant complex and increases reliance on prosthetic screw performance. Despite growing clinical and commercial interest in these systems, the available evidence remains limited and fragmented, and the biomechanical consequences of removing the titanium base have not been clearly synthesized. Therefore, this critical review evaluated the influence of prosthetic screw design on the biomechanical behavior of titanium base-free MUA restorations, focusing on preload maintenance, load transfer, and mechanical stability. The evidence indicates that preload loss, screw loosening, and fatigue behavior are primary determinants of mechanical performance. Screw material, surface characteristics, and head geometry may affect preload generation, load distribution, and resistance to micromovement, although current evidence remains limited and heterogeneous. Short-term clinical outcomes appear acceptable when appropriate biomechanical and prosthetic protocols are followed; however, long-term comparative data are lacking. Titanium base-free MUA restorations should be considered a technique-sensitive approach requiring optimized screw selection, accurate prosthetic fit, and controlled occlusal loading. Further well-designed long-term studies are needed to establish their predictability.