A Comparison of Accuracy of Different Dental Restorative Materials between Intraoral Scanning and Conventional Impression-Taking: An In Vitro Study

Abstract

The properties of underlying substrates influence the quality of an intraoral scan, but few studies have compared the outcomes using common restorative materials. In this study, we aimed to compare the accuracy of digital and conventional impressions recorded for four different dental materials as the substrates. Experimental crowns were produced with a metallic surface (gold or cobalt-chromium alloy (Co-Cr)) or without a metallic surface (zirconia or PMMA (polymethyl methacrylate)). A conventional impression was made in the conventional group (CON group), and gypsum models were subsequently scanned with a tabletop scanner. An intraoral scanner was used to scan the crowns either after applying a powder spray to reduce the surface reflectivity (IOS-P group) or without the powder spray (IOS group). The scans were assessed in three dimensions for precision and trueness. The accuracy did not differ between the CON and IOS groups for the non-metallic crowns. However, it was statistically different for the Co-Cr metallic crown, reducing trueness observed between groups as CON > IOS > IOS-P. The study evidences the differences in outer surface accuracy observed with a change in the substrate material to be imaged using an oral scanner and with the impression method. These findings suggest that the restoration material present in the oral cavity should be considered when selecting an impression-taking method.

Keywords: CAD/CAM; accuracy; crown substrate; dental restorative materials; digital impression; intraoral scanner; powder spray.

Figure 1

Flow chart of the study design for comparing accuracies between the two impression-taking protocols. Eight impressions were recorded for each material in accordance with the methodology of each group. CAD, computer-aided design; CAM, computer-aided manufacturing; CON, conventional; IOS, intraoral scan; and IOS-P, intraoral scan with powder.

Figure 2

Comparison of non-metallic restorative materials using different impression-taking protocols. (A) Precision; (B) trueness. Different uppercase letters indicate significant differences between groups within a category on the x-axis. Different lower-case letters indicate significant differences between two materials for the same impression-taking protocol. Each box plot shows the median, first and third quartiles, and range. CON, conventional; IOS, intraoral scan; and IOS-P, intraoral scan with powder.

Figure 3

Comparison of metallic restorative materials using different impression-taking protocols. (A) Precision; (B) trueness. Different uppercase letters indicate significant differences between groups within a category on the x-axis. Different lower-case letters indicate significant differences between two materials for the same impression-taking protocol. Each box plot shows the median, first and third quartiles, and range. CON, conventional; IOS, intraoral scan; and IOS-P, intraoral scan with powder.

Figure 4

(A) Trueness comparison between different restorative materials using the intraoral digital impression-taking protocol. The asterisk indicates a significant difference from the other groups (p < 0.05); (B) Color maps showing the outcome of morphometric comparison, with positive deviations (larger than reference) and negative deviation (smaller than reference) between the materials for the different crown surfaces.