Implant-Abutment Interface Gels in Two-Piece Implant Systems: The "Guardian-Hazard" Paradigm-A Scoping Review

Background/Objectives: Antiseptic gels applied at the implant-abutment interface (IAI) aim to reduce microbial leakage and peri-implant inflammation. However, introducing viscous media into a precision screw joint may affect tribology, preload maintenance, mechanical stability and corrosion-related processes. This scoping review mapped evidence on chlorhexidine (CHX) and other IAI gels, considering their biological, mechanical and electrochemical effects. Methods: Following PRISMA-ScR and a Population-Concept-Context framework, in vitro, in vivo and clinical studies of two-piece implant systems were eligible if they evaluated CHX or another sealing gel at the IAI and reported microbial, mechanical or electrochemical outcomes. English-language full texts published between 2015 and 2025 were identified through PubMed/MEDLINE, Scopus, ScienceDirect and reference screening. Findings were synthesised qualitatively within "Guardian" (biological protection) and "Hazard" (mechanical or electrochemical effects) domains. Results: Of 241 records, 16 met the inclusion criteria. CHX gels reduced intra-implant bacterial counts, although their sealing effect was limited and time-dependent. Silicone-based sealants generally achieved better microbial leakage control and, in several studies, maintained or increased reverse torque values compared with dry controls. Conversely, aqueous or oil-based antiseptic agents frequently reduced reverse torque, suggesting lubrication-related effects on screw-joint stability. No study directly quantified tribocorrosion associated with specific gels. Conclusions: IAI gels may provide biological protection, but their effects depend on formulation and are not exclusively antimicrobial. Silicone-based materials demonstrated the most favourable combined microbial and mechanical performance. Tribocorrosion remains insufficiently investigated, highlighting the need for integrated microbial, mechanical and electrochemical studies.