In vitro assessment of the accuracy of digital impressions prepared using a single system for full-arch restorations on implants

Purpose: This study describes a method for measuring the accuracy of the virtual impression. Methods: In vitro measurements according to a metrological approach were based on (1) use of an opto-mechanical coordinate measuring machine to acquire 3D points from a master model, (2) the mathematical reconstruction of regular geometric features (planes, cylinders, points) from 3D points or an STL file, and (3) consistent definition and evaluation of position and distance errors describing scanning inaccuracies. Two expert and two inexpert operators each made five impressions. The 3D position error, with its relevant X, Y, and Z components, the mean 3D position error of each scanbody, and the intra-scanbody distance error were measured using the analysis of variance and the Sheffe’s test for multiple comparison. Results: Statistically significant differences in the accuracy of the impression were observed among the operators for each scanbody, despite the good reliability (Cronbach’s α = 0.897). The mean 3D position error of the digital impression was between 0.041 ± 0.023 mm and 0.082 ± 0.030 mm. Conclusions: Within the limitations of this in vitro study, which was performed using a single commercial system for preparing digital impressions and one test configuration, the data showed that the digital impressions had a level of accuracy comparable to that reported in other studies, and which was acceptable for clinical and technological applications. The distance between the individual positions (#36 to #46) of the scanbody influenced the magnitude of the error. The position error generated by the intraoral scanner was dependent on the length of the arch scanned. Operator skill and experience may influence the accuracy of the impression.