Objective: The purpose of this study was to assess the impact of photopolymer resin type, arch location, and post-processing techniques on the trueness and precision of three-dimensionally printed (3DP) full-arch surgical implant guides. Methods: Stereolithography reference images of an upper and lower surgical guide with six drill holes from a full-mouth rehabilitation clinical case were used. The files were imported into the Asiga MAX UV slicing software (Asiga Composer) where build orientation, print resolution, and support structures were added. A digital light processing 3D printer (MAX UV, Asiga Max) was used for printing the samples. The samples assessed were printed using two different, manufacturer-validated resins, DentaGuide (n = 35) and DentaClear (n = 20). The samples were subdivided and measured based on the post-processing technique used: handwashing (n = 20), sonication (n = 25), a mix of handwashing and sonication (n = 10), and post-curing using 385 nm UVA light with nitrogen (n = 50) or without nitrogen (n = 5). The diameter of each drill hole per guide was measured using a coordinate measuring machine (Absolute Arm 7-Axis, Hexagon) and compared with the reference STL to calculate each sample’s trueness (median error) and precision (interquartile range). The Mann–Whitney and Kruskal–Wallis tests were used for statistical analyses. Results: All samples demonstrated a dimensional error of <70 µm. No significant differences (p > 0.05) were observed between upper and lower arches and between post-processing techniques using nitrogen, irrespective of the use of hand- or ultrasonic washing. In contrast, DentaClear resin was significantly (p < 0.001) more accurate with a trueness of 26 µm and precision of 12 to 34 µm versus the DentaGuide at −31 µm and −54 to −17 µm, respectively. The samples post-cured without nitrogen were significantly (p < 0.05) the least accurate of all surgical guides, with a trueness of −42 µm and precision of −68 to −39 µm. Conclusion: The resin type and nitrogen post-processing are parameters that can significantly impact the accuracy of surgical guides. The tolerance of 3DP surgical guides needs to account for the dimensional changes occurring during the manufacturing process to minimise implant positioning errors.