Influence of the Number of Implants on the Accuracy of Complete-Arch Impressions: In Vitro Comparison of Photogrammetry and Intraoral Scanners Using a Coordinate Measurement Machine.

OBJECTIVE: To evaluate the influence of the number of implants on the accuracy of complete-arch implant impressions using different photogrammetry systems and an intraoral scanner, and to assess the effect of scan body repositioning on impression reproducibility. METHODS: Three maxillary stone casts containing four, six, and eight implants, respectively, were manufactured. Impressions were obtained using four techniques: extraoral photogrammetry (PG), navigated photogrammetry (NPG), intraoral photogrammetry (IPG), and intraoral scanner (IOS). For each configuration, ten impressions were recorded under fixed scan body conditions and ten with two repositioned scan bodies. A coordinate measurement machine (Wenzel LH 8-15-7, Germany) provided reference coordinates. Linear deviations were assessed by the root mean square (RMS, mm) and the angular deviation was calculated as the mean of absolute angular deviations (MEAN-D, °) using custom-developed software. Experimental data were analyzed using linear regression analysis (p < 0.05). RESULTS: Photogrammetry systems demonstrated superior accuracy to intraoral scanning. PG achieved the lowest linear deviation (0.037 mm) followed by IPG (0.057 mm) and NPG (0.077 mm), whereas IOS exhibited the highest deviations (0.099 mm). Mean angular deviation (MEAN-D) was 0.16° (PG), 0.40° (IPG), 0.33° (NPG), and 0.78° (IOS). Regression analyses showed that RMS increased with the number of implants, while MEAN-D decreased. Significant differences were found between all impression techniques, while scan body repositioning had no clinically meaningful effect across systems. Overall precision (CV) was 24.9% for RMS and 28.6% for MEAN-D, and for both parameters precision was highest for PG and lowest for IOS. CONCLUSIONS: Under the conditions of this in vitro study, photogrammetry provides superior accuracy (trueness and precision) compared to intraoral scanning for complete-arch implant impressions. The number of implants influences accuracy, whereas scan body repositioning has minimal effect. CLINICAL SIGNIFICANCE: These findings highlight the in vitro performance of photogrammetry systems and their potential applicability in complete-arch digital implant workflows.