Accuracy in the Interface between Implant Components after a 5-year Functional Period; A Clinical Report

Abstract

The reduction in the assembly accuracy of the implant complex could result from fatigue and micromovement during the functional phases and from the manufacturing process. The long-term functional integrity of implant prostheses can be ensured by accurate fit of the interfaces between the assemblies from a biomechanical perspective. A single implant restoration on the mandibular left first molar was removed after a 5-year functional period due to mobility, which was diagnosed as abutment screw loosening. The superstructure could not be retrieved, despite exceeding the torque value recommended by the manufacturer; therefore, the restoration was unscrewed and removed. The retrieved restoration, particularly the configuration of the abutment-gold cylinder and abutment-retaining screw interfaces, was analyzed with scanning electron microscopy. Moreover, the assembly accuracy of the old and new assemblies was compared. In the new specimen, a relatively an even linear gap was found between the threads of the abutment and screw and no vertical marginal gaps were found at the abutment-cylinder interface, wherein the horizontal and vertical contacts were incomplete. In the old specimen, an irregular pattern of screw-thread engagement, an irregular linear space at the abutment-cylinder interface, a partially worn-out screw configuration and remnants of the screw in the interface were observed.