The aim of this in vitro study was to evaluate the accuracy of impressions made using two different silicones and corresponding stone casts in full-arch implant rehabilitation, using two laboratory scanners. A master model with six dental implants was created, scanned with a 12-megapixel scanner and used as digital master model. Ten implant impressions were obtained via two silicone impressions systems—Coltene® and Zhermack®—using the open-tray technique and poured gypsum. Two extraoral scanning systems (S600 ARTI Zirkonzhan® and Identica T500 Medit®) were used to scan the impressions and stone casts. Best-fit superimpositions were conducted between the master model and the virtual models obtained. A significance level of p < 0.05 was considered. The accuracy of the Medit® scanner was 82.26 [53.18; 111.34] µm for Coltene® silicone and 87.43 [72.00; 102.86] µm for Zhermack® silicone, and the accuracy of the Zirkonzhan® scanner was 69.90 [62.37; 77.43] µm for Coltene® silicone and 80.67 [65.77; 95.57] µm for Zhermack® silicone, without significant differences between scanners. When comparing the two silicones, no significant differences were found for the Medit® (p = 0.112) or Zirkonzhan® scanners (p = 0.162). The Zhermack® scanner showed better accuracy than the corresponding stone casts in the two scanners, Medit® (p = 0.019) and Zirkonzahn® (p = 0.002). The extraoral digitalization of impressions in edentulous dental arches with six implants proves to be a valid technique.