Abstract
Background: Digital technologies, particularly CAD/CAM workflows, have transformed implant prosthodontics by improving the accuracy and efficiency of impression procedures, facilitating clinician-laboratory communication, and supporting the preservation of peri-implant tissues. Objective: To compare the three-dimensional accuracy (trueness) and passive fit of five conventional and digital impression techniques for fixed prostheses supported by two implants. Methods: An in vitro experimental study was conducted using a partially edentulous maxillary model with two implants supporting a three-unit zirconia bridge. Five impression workflows were evaluated: conventional techniques (open-tray and closed-tray, splinted and non-splinted) and digital impressions using plastic and titanium scan bodies. Three-dimensional accuracy was assessed by digital superimposition analysis, and passive fit was evaluated by marginal gap measurements using digital microscopy and ImageJ (version 1.54r) software. Statistical analyses were performed using exploratory ANOVA with Welch's correction and Games-Howell post hoc tests (p < 0.05), complemented by effect size analysis. Results: Three-dimensional superimposition analysis revealed that digital impression workflows and the splinted conventional open-tray technique exhibited the highest trueness, with minimal spatial deviations relative to the reference model, together with the lowest marginal gap values (<1 µm). The non-splinted open-tray technique presented higher discrepancies (7.37 ± 0.94 µm), although all techniques remained within clinically acceptable tolerance ranges (60-150 µm). Conclusions: Under controlled in vitro conditions, both digital impression techniques and conventional splinted protocols achieve high three-dimensional accuracy and clinically acceptable passive fit for multi-implant-supported fixed prostheses. Digital workflows represent a predictable and efficient alternative, while conventional splinted impressions remain a reliable option depending on clinical and technological considerations.