Accuracy of Conventional and Digital Impressions for Complete-Arch Implant-Supported Restorations

Objective  To evaluate the accuracy of conventional impression techniques, intraoral scanning, and two stereophotogrammetry systems (PIC and ICam4D) for complete-arch implant restorations, and to analyze the influence of varying interimplant distance and implant angulation on the accuracy of each impression method.

Methods  A total of 6 edentulous maxillary all-on-four casts were fabricated with varying posterior implant parameters, including anterior-posterior (A-P) distances of 20 mm and 35 mm and distal implant angulations of 0°, 15°, and 25°. Impressions were obtained using conventional impression techniques, intraoral scanning, and two stereophotogrammetry systems (PIC and ICam4D). The three-dimensional deviations of the impression techniques were measured using reverse-engineering software to evaluate trueness and precision.

Results  The accuracy of intraoral scanning technology exhibited a declining trend with increasing A-P distance and implant angulation. The maximum deviations in trueness and precision were observed in the posterior region with an A-P distance of 35 mm and a distal implant angulation of 25°, measuring (76.90 ± 43.32) μm and (99.43 ± 74.39) μm, respectively. The conventional impression techniques exhibited stable performance, with mean accuracy deviation values consistently falling below 50 μm. The ICam4D stereophotogrammetry system exhibited the highest precision across all conditions (P < 0.05). The maximum precision deviation for PIC system occurred in the right anterior region with an A-P distance of 20 mm and a distal implant angulation of 15° (28.10 ± 18.73 μm), while the maximum trueness deviations for both PIC and ICam4D were observed in the anterior region with an A-P distance of 20 mm and a distal implant angulation of 25°, measuring (62.63 ±9.40) μm and (83.61 ± 1.76) μm, respectively. The PIC system showed better overall trueness than ICam4D did when distal implant angles were ≥ 15° (P < 0.05).

Conclusion  For complete-arch implant rehabilitation, the accuracy of different impression methods varies depending on implant-related factors. The inter-implant distance and angulation were critical determinants of accuracy for intraoral scanning, whereas conventional impression techniques and the two stereophotogrammetry systems exhibited no clear correlation with these parameters.