Intermediate and Multi-Unit Abutments in Implant-Supported Restorations: When, Why, and How to Use Them, a Narrative Review

Background/Objectives: This narrative review aimed to critically assess the role of multi-unit abutments in implant dentistry, focusing on mechanical reliability and biological stability at the implant–abutment interface. Methods: A literature search was performed in PubMed/MEDLINE, Scopus, Web of Science and Google Scholar to identify clinical studies and experimental research from the past 20 years addressing implant–abutment connections, mechanical complications and biological integration of multi-unit abutments. Results: Dental implants demonstrate survival rates above 95%, yet complications, up to 35%, are primarily linked to the implant–abutment interface. Mechanical issues, especially screw loosening, may be mitigated with conical connections and adherence to evidence-based protocols. Biologically, multi-unit abutments with sufficient transmucosal height contribute to stable supracrestal tissue and preservation of marginal bone. Advances such as nanostructured surfaces and the concept of mucointegration represent a shift toward biologically active interfaces, enhancing peri-implant soft tissue health. Conclusions: Multi-unit abutments have evolved from simple angulation-correction tools to essential components across a wide range of clinical applications. Their success relies on strategic, protocol-driven use that integrates mechanical strength with biological harmony, enabling potentially favorable outcomes in modern implant dentistry, particularly in well-selected clinical scenarios.