Digital Accuracy of Closed-Tray Implant Impressions: Influence of Polyvinyl Siloxane Viscosity and Subgingival Posterior Implant Angulation

Objectives: To assess the impact of PVS impression material viscosity and implant angulation on the three-dimensional accuracy of implant casts in a partially edentulous situation using the closed-tray technique. Materials and Methods: Three epoxy resin mandibular partially edentulous models (Kennedy Class I) were fabricated, each with four implant analogues placed at teeth positions 35, 37, 45, and 47. The anterior analogues were positioned parallel (0), while the posterior analogues were placed at different angulations: Group 1, 30° mesiodistal; Group 2, 20° mesiodistal; Group 3, 20° buccolingual. All analogues were placed 2 mm subgingivally. Closed-tray impressions (n = 8 per subgroup) were made using either heavy + light body PVS or monophase PVS. Resulting stone casts were scanned, and STL files were processed and analyzed using reverse engineering software (Geomagic Control X). Three-dimensional deviations (root mean square, RMS) between reference and test models were calculated by superimposition and best-fit algorithm. Results: With monophase PVS, implant angulation significantly influenced cast accuracy (p < 0.001). The 30° MD group exhibited the highest deviation (96 ± 7 µm), followed by the 20° BL group (81 ± 6 µm), then the 20° MD group (75 ± 6 µm). In contrast, no statistically significant difference in accuracy was observed among angulation groups when using heavy + light body PVS (77 ± 3 µm, 82 ± 13 µm, and 79 ± 8 µm for 30° MD, 20° BL, and 20° MD, respectively; p = 0.550). Conclusions: Both monophase and heavy + light body PVS impression materials produced clinically acceptable accuracy for closed-tray implant impressions. However, the heavy + light body PVS demonstrated greater consistency across various implant angulations and is recommended for multiple angulated subgingival posterior implants when using the closed-tray technique.