In vitro evaluation of the strength of the conical implant-to-abutment joint in two commercially available implant systems

Statement of problem. The cone-screw abutment has been shown to diminish micromovement, reducing the burden of component loosening and fracture. However, it is unclear whether the conical taper and joint design influence strength of the interface, with respect to unfavorable bending moments. Purpose. This comparative study evaluation the resistance to bending for the ITI Straumann and Astra Tech ST implant systems using an 8- and 11-degree internal cone, respectivtely. Material and methods. Assembled units from each system were mounted in a 3-point bending apparatus. High load tests were performed, 4 mm from the joint, and bending moments necessary to induce first point of plastic deformation and ultimate failure were measured. All units were inspected to determine the critical zone of failure. Results. Bending moments necessary to induce first point of plastic deformation were considered well above that expected in clinical function for both systems. However, the critical zones of failure differed in that the solid Astra. abutment deformed before the cone joint with its 11-degree taper and smooth transition into the neck of the screw preventing screw fracture. By contrast, all ITI screws fractured at the head of the screw where it met the base of the 8-degree cone. It is unclear which aspects of the joint design were responsible for the difference observed in mode of failure or if it nas a direct result of the experimental design. Conclusion. For clinically relevant levels of bending moment, no problems were anticipated with respect to component failure for either system.