Rescanning of Digital Impressions' Mesh Holes: In Vivo and In Vitro Accuracy Evaluation of Three Different Scanning Protocols

Several factors have been identified to have an influence over the accuracy of a digital impression: ambient lighting conditions, the presence of liquid on the intraoral structures, and the scanning patterns. The purpose of this study was to identify which protocol produced the most accurate digital impression regarding a one-preparation scenario in which data were acquired from a single uninterrupted scan, a rescanning of the area of interest in order to obtain more data, or the deletion of the area of interest followed by a rescan. An in vitro scenario using a typodont involving a single full-crown restoration was conceived alongside the selection of an in vivo case of a patient presenting an unrestored right mandibular first molar. The STL (standard tessellation language) reference models for each group were obtained using a high-resolution scanner (Freedom, HD; DOS). With the use of a Medit I700 (Medit, Seoul, South Korea) intraoral scanner, three different scanning protocols were conducted on the typodont and on the clinical case. The measured data (IOS scans) were sorted and further analyzed with the help of Geomagic Control X (Version:16.0.2.16496, 3D Systems, Wilsonville, OR, USA). The Kolmogorov-Smirnov test for normality was conducted on the whole set of data. The nonparametric data set underwent Kruskal-Wallis test analysis while the parametric data set underwent a one-way ANOVA test (the level of significance was set to alpha = 0.05). For the in vitro case, the "SINGLESCAN" group displayed the best trueness; the "DELETE&RESCAN" group displayed the best precision. Regarding the in vivo case, the "SINGLESCAN" group also displayed the best trueness; the "RESCAN" group displayed the best precision. Statistical differences were found in the trueness and precision of the IOS scans captured with the three different scanning protocols, but the differences were so small that they could be considered clinically negligible.