Do "cut out-rescan" procedures have an impact on the accuracy of intraoral digital scans?

Abstract

Statement of problem: The software programs of digital intraoral scanners typically offers the option to cut out areas from 3D casts, to do rescans, and to merge them with the initial scan. However, evidence of whether this procedure has an impact on the accuracy of the scan is lacking.

Purpose: The purpose of this study was to determine whether "cut out-rescan" procedures change the accuracy of a 3D cast.

Material and methods: A maxillary master cast was digitized with an industrial structured light scanner to obtain a digital reference cast. This master cast was repeatedly scanned by 3 intraoral scanners: TRIOS 3 [TR], Cerec Primescan [PR], and Cerec Omnicam [OM]. The scan data were duplicated, and the posterior area from the right lateral incisor was cut out and rescanned to obtain complete-arch casts containing the rescanned data [TR_rs], [PR_rs], and [OM_rs]. The trueness and precision of the scans were evaluated by superimposing procedures of the relevant data sets. To evaluate statistical differences, either the Mann-Whitney U test or the t test was used (α=.05).

Results: The median precision values of the complete-arch scan data was 19 μm for [OM] and [TR], whereas the median for [PR] was 14 μm. In the "cut out-rescanned" data group, the values were 25 μm for [OM_rs], 16 μm for [TR_rs], and 14 μm for [PR_rs]. Statistically significant differences were found among the scanners [OM]/[PR], [OM_rs]/[TR_rs], and [TR_rs]/[PR_rs]. The mean ± standard deviation values of trueness for the complete-arch scan data were 54 ±4 μm for [OM], 42 ±5 μm for [TR], and 30 ±2 μm for [PR]. In the group of the "cut out-rescanned" data, the mean trueness results were 55 ± 6 μm for [OM_rs], 38 ±5 μm for [TR_rs], and 31 ±5 μm for [PR_rs]. Significant differences were found among the complete-arch scan data and the "cut out-rescanned" data of the different scanners, but not between the complete-arch scan data and the "cut out-rescanned" data within one scanning system.

Conclusions: Significant differences were found among the scanners, but "cut out-rescan" procedures did not affect the accuracy within each scanning system.