Factors associated with loosening of abutment screws in implant-supported dental prosthesis: literature review of 100 articles with best match recommendation by PubMed

The advent of osseointegration had a fundamental impact on the field of prosthetic rehabilitation of different types of edentulism, from single to multiple failures. However, implants are subject to biological and mechanical complications. Among the mechanical complications, the most frequent is loosening of abutment screws (LAS) in single crowns. As result of the LAS, the gaps between the implant platform and the dental crowns favor bacterial accumulation and can generate a gingival inflammatory, screw fractures and great discomfort to the patient. The objective of this review is to present and discuss the factors and mechanisms associated with the LAS. The bibliographic search was carried out on the website of “Pubmed.gov-National Library of Medicine and National Center for Biotechnology Information in August 2021, using the terms “loosening AND dental implant AND abutment screw” and selecting the first 100 articles by the best recommendation icon (“best match”). The information was grouped by the following factors associated with the LAS: 1) Types of implant-abutment connection; (2) The geometric morphology and the material used and the abutment fabrication; (3) The abutment screw design; (4) The abutment design; (5) implant design, (6) torque value, (7) The material used in making the prostheses, and (8) associated clinical-practical factors. Important knowledge is oriented to clinicians in this review to minimize the occurrence of LAS, however, a critical evaluation shows that the results of the studies present a limited consensus on the theme, so additional studies are needed for ideal conclusions about practices and methodologies for reducing LAS.