INTRODUCTION: Mechanical complications of the implant-abutment system include screw loosening, micromovements, fracture of the maintaining screw, abutment, suprastructure, or implant. Screw loosening is the most common of them, leading to a micro-gap which is contaminated with microorganisms. Thus, biological complications, such as peri-implant mucositis and peri-implantitis, occur.
AIM: The purpose of this literature review is to analyze the factors that influence screw loosening and microleakage between the implant and the abutment after cyclic loading.
MATERIALS AND METHODS: Review papers and case reports from the Scopus, PubMed, and ScienceDirect databases were used for the purpose of this review. The bibliography of the selected articles was additionally analyzed.
RESULTS: The influence of the main factors on the screw loosening and microleakage between the implant and the abutment after cyclic loading was analyzed in light of the significance of each factor. The contradictory results were found concerning in terms of the influence of the collar length and the abutment angulation on the screw's loosening. On the one hand, screw loosening increases with increasing the collar length and angulation degree. On the other, some researchers claim that there is no relationship between the collar length, abutment angulation, and screw loosening after cyclic loading. In regard to the implant-abutment connection design, it was found that the internal and external hexagon connections are less resistant to screw loosening and microleakage than Morse tapper implants. The interior hexagon connection showed better torque maintenance than the external hexagon connection. The last two factors—implant diameter and screw length had no strong influence on the screw loosening after cyclic loading.
CONCLUSION: It was found that the main factors affecting the screw loosening and microleakage between the implant and the abutment after cyclic loading were angulation and collar length of the abutment, implant-abutment connection design, implant diameter, and screw length.
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