Digital and Conventional Impression Techniques for Subgingival Finish Lines in Tooth-Supported Fixed Prosthodontics: A Scoping Review

Background: Accurate reproduction of subgingival finish lines remains a major challenge in fixed prosthodontics. This scoping review aimed to map and synthesize current evidence comparing digital and conventional impression techniques for tooth-supported restorations with subgingival margins. Methods: The review followed the Arksey and O’Malley framework and was reported in accordance with PRISMA-ScR guidelines. Four electronic databases (PubMed, Scopus, Web of Science, and Google Scholar) were searched for English-language studies published between 2005 and 2025. Eligible studies included both in vitro and in vivo investigations evaluating impression techniques in subgingival conditions. Results: A total of 51 studies were included, of which 66.6% were in vitro. Digital scanning accuracy decreased consistently as subgingival depth increased, particularly beyond approximately 1 mm below the gingival margin. Conventional elastomeric impressions generally demonstrated more consistent reproduction of deeper subgingival margins. Conclusions: Impression accuracy in subgingival conditions appears to depend primarily on finish line depth and clinical conditions rather than on impression modality alone. Digital workflows appear reliable for equigingival and shallow subgingival margins, whereas conventional or hybrid approaches may remain advantageous in deeper subgingival scenarios. Further well-designed in vivo studies using standardized measurement protocols are needed to support evidence-based clinical recommendations.