Linear Accuracy of Full-Arch Digital Models Using Four Different Scanning Methods: An In Vitro Study Using a Coordinate Measuring Machine

Abstract

Improving the accuracy of the digital model is essential for the digitalization of the dental field. This study introduced a novel method of objective accuracy evaluation of digitized full dental arch model using coordinate measuring machine (CMM). To obtain a true linear measurement value using the CMM, 17 reference balls were attached to the typodont, and 12 measurements between balls on the X-(width), Y-(length), and Z-axes (height) were performed automatically. A rubber impression and a plaster cast replica of the typodont with balls were fabricated, and they were digitized with following methods: (a) true model intraoral scans; (b) impression cone-beam computed tomography (CBCT) scans; (c) cast CBCT scans; and (d) cast extraoral scans. Each scanning method was performed 20 times. Twelve linear measurements on the digitized models were automatically made using software. The one-sample t-test and one-way analysis of variance were used for measurement accuracy analysis. The cast extraoral scan was most accurate on X-and Y-axes, while impression CBCT was the most accurate on Z-axis. Over all axes, the intraoral scan resulted in the most deviation from the true model, and the reproducibility of each scan was also low. Extraoral scan shows high precision on width and length, and impression CBCT is advantageous for dental work where height factor is of importance.

Dimensional Accuracy of Digitalized Stone Models Obtained from Alginic Acid Polymer and Poly-dimethyl-siloxane Impressions

“…A general "shrinkage" of the digitalized models was observed after scanning comparing to the reference model (Table 1 and Table 2). This fact was also reported in previous studies [25,70,71] and researchers suggested that this tendency of "downsizing" of the digital models might be due to the algorithms used in the conversion software [71,72]. Digital models with statistically significant smaller measurements than the true measurements were also obtained by Kim et al who used for digitalization of plaster models intraoral scanners, desktop scanners and CBCT scan [25], downsized virtual models being obtained with all digitalization techniques.…”

“…This fact was also reported in previous studies [25,70,71] and researchers suggested that this tendency of "downsizing" of the digital models might be due to the algorithms used in the conversion software [71,72]. Digital models with statistically significant smaller measurements than the true measurements were also obtained by Kim et al who used for digitalization of plaster models intraoral scanners, desktop scanners and CBCT scan [25], downsized virtual models being obtained with all digitalization techniques. However, it should be note that, in the present study, when AAP was used as impression material, the errors were "compensated" and the obtained digital model was not statistically significant different to the reference model, in all measured parameters (Table 3).…”

“…Due to the extensive requirements of digitalization of conventional models, in partially digital workflows, a great number of studies were performed recently on the accuracy of full arch digital models [20,22,25,45,48,49], assessing different type of scanners used to digitalize the gypsum models [45], different scanning techniques [25], comparing different type of impression materials to digital https://doi.org/10.37358/MP.20.3.5384 impressions [20,22], but the evaluation of the factors involved in indirect digitalization such as the influence of the impression materials or techniques on the accuracy final digital model is limited.` The present study aimed to assess the accuracy of full arch models, obtained by pouring impressions from two different materials and two techniques frequently used for arch registration for implant planning, orthodontic treatment or prosthetic rehabilitation, before and after indirect digitalization.…”

“…Kim et al uses the measurement of surface reference points with high trueness coordinate measurement machines (CMMs) [25], but with some shortcomings such as lack in scan speed and less accurately in measuring freeform surfaces because of the geometric size and shape of the tip (probe) [52]. However, in our study the analog measurements of the typodont model was considered as references, therefore a digital caliper was used for measuring all analog models and the digital models were measured in Exocad software, with the dedicated measurement tool.…”

“…Moreover, the absence of marked reference points and the solely use of virtual marks, as cusps or fossae, could lead to significant differences between measurements with low intra-and interobserver reliability [24,25].…”