The Influence of a Positioning Hex on Abutment Rotation in Tapered Internal Implants: A 3D Finite Element Model Study

Purpose: The purpose of this study was to investigate the resistance against rotation of a two-piece abutment with or without the presence of a positioning hex in tapered internal connection implant systems. Materials and Methods: A tapered internal connection implant with an 11-degree internal oblique angle was placed into a constructed three-dimensional (3D) bone model. Two types of abutments were compared: hex-type abutments with a positioning hex and two-piece round-type nonhex abutments. Vertical compressions equivalent to the screw tightening torque of 30 Ncm and 40 Ncm were applied to the abutment screws. A horizontal load of 150 N was applied to the superstructure to create moments. The contact area between the implant and abutment was compared and analyzed. The rotational displacement of the abutments was investigated as well. Results: When a preload equivalent to 40 Ncm of tightening torque was applied, the round-type abutment exhibited a larger contact area than the hex-type abutment by approximately 2.5% to 3.5% in contrast to the internal surface area of the implant. When the screw tightening torque of 30 Ncm was applied, the rotational displacement of the hex-type abutment was approximately 0.54 degrees and the round-type was approximately 1.16 degrees under clockwise moment loading. Conclusion: Within the limitations of this study, it can be assumed that the hexagonal design of the abutment acts as rotational resistance against moments. Keywords: 3D finite element model, implant rotation, positioning hex, tapered internal implant, von Mises stress