Stability of Implant-Abutment Connection After Using the Rescue Kit: An in Vitro Study

Purpose: To evaluate whether removing a fractured abutment screw with a specific rescue device negatively affects the success of a new restoration in terms of early abutment loosening. Materials and Methods: Implants (n = 10) with a regular platform of 4.1 mm (tissue level [TL]) and implants (n = 10) with a reduced diameter of 3.3 mm (bone level [BL]) were used. The screws of eight respective abutments for both implant types were artificially weakened in order to fracture during torque application for abutment insertion. The fractured abutment screws were removed applying a specific rescue kit. The implant inner threads were cleaned and remodeled with a system-specific tapper. New abutments were inserted, and computer-aided design/computer-aided manufactured (CAD/CAM) full zirconia crowns were luted. Aging by thermal cycling and mechanical loading was performed with a customized masticator simulator, and the number of crown and/ or abutment loosenings was determined. In cases in which no loosening was observed, sawing and grinding were performed to determine the contact zone between the inner implant thread and abutment screw. Data were compared with a control group, eg, unmodified implant-abutment connections. Results: No abutment loosening was observed. All crowns were in function after mastication simulation. The inner thread contact zones of both test groups were generally smaller than in the control group, with a mean contact area of 448.6 μm and 459 μm for BL implants, and 608.8 μm and 620.5 μm for the TL implants in test and control groups, respectively. Conclusion: Removing a fractured abutment screw with a specific rescue device and modifying the inner thread seems not to negatively affect the functional connection between a new abutment and the implant. Keywords: CAD/CAM, mastication, screw, torque, zirconia crowns