Effect of surface modification on the long-term stability of dental implant abutment screws by plasma nitriding treatment

Abstract

The mechanical behavior plays a key role in the long-term stability of dental implants. The loosening of abutment screws is one of the most common problems. Plasma nitriding treatment (PNT) is a recently developed method of in situ surface modification to solve the screw loosening problem. In this study, we investigated the effect of plasma nitriding on the dental implant abutment screw joint. Abutment screws were treated with plasma nitriding. The preload force and friction coefficient of the screw were measured. The single fracture load (SFL) test and dynamic fatigue life (DFL) test were performed to test the fatigue performance of the implant screw connection. The fracture location is verified by the finite element analysis (FEA). Then, the loosening torque of the screw under static and dynamic loads was measured. Finally, the surface fracture morphology of the implant system and surface wear morphology of the screw were observed. The results show that the PNT could reduce the friction coefficient and increase the preload force. Plasma nitriding significantly affected the fatigue property. The PNT increased the fracture load and elongated the fatigue life. In addition, the PNT improved the anti-loosening performance under dynamic load. Most of the fatigue fracture occurred at the neck region of the implants and the first thread of the abutment screws, consistent with the FEA results. Plasma nitriding can reduce the wear of screw surfaces and protect the integrity of the thread. Therefore, the PNT effectively improves the long-term stability of the implant system.