Influence of rescanning mesh holes on the accuracy of an intraoral scanner: An in vivo study

Abstract

[EN] Objectives: To evaluate whether the cutting-off and rescanning procedures have an impact on the accuracy (trueness and precision) of the intraoral digital scan. Methods: A right quadrant digital scan (reference scan) of a participant was obtained using an intraoral scanner (IOS) (TRIOS 4; 3Shape A/S, Copenhagen, Denmark). The reference scan was duplicated 135 times and divided into 3 groups based on the number of rescanned mesh areas: 1 (G1 group), 2 (G2 group), and 3 (G3 group) mesh holes. Each group was subdivided into 3 subgroups depending on the mesh hole diameter: 2 mm- (G1-2, G2-2, and G3-2), 4 mm- (G1-4, G2-4, and G3-4), and 6 mm- (G1-6, G2-6, and G3-6) (n = 15). A software program (Geomagic; 3D Systems, Rock Hill, SC, USA) was used to assess the discrepancy between the reference and the experimental scans using the root mean square (RMS). Kruskal-Wallis and post hoc multiple comparison Dunn's tests were used to analyze the data (alpha=0.05). Results: Trueness ranged from 5 to 20 mu m and precision ranged from 2 to 10 mu m. For trueness assessment, KruskalWallis test revealed significant differences on the RMS error values among the groups tested (P<.05). The G3-6 group obtained the lowest trueness and lowest precision values, while the G1-2, G1-4, G2-2, G2-4, and G3-2 groups computed the highest trueness and precision values. When comparing groups with the same number of rescanned mesh holes but with different diameter, the higher the diameter of the rescanned mesh hole, the lower the trueness values computed; however, when comparing groups with the same diameter of the rescanned mesh hole but with differing number of rescanned mesh holes, no significant differences were found in the RMS values among the groups. For the precision evaluation, Levene's test showed a lack of equality of the variances, and therefore of the standard deviations. The F-test with Bonferroni correction identified significant differences between the SDs between group G3-6 and all the other groups. When comparing instead the interquartile range (IQRs) due to the non-normality of the data, groups G1 and G2 also showed lower IQR values or higher precision than groups G3. Conclusions: Cutting-off and rescanning procedures decreased the accuracy of the IOS tested. The higher the number and diameter of the rescanned areas, the lower the accuracy. Clinical significance: Cutting-off and rescanning procedures should be minimized in order to increase the accuracy of the IOS evaluated. The intended clinical use of the intraoral digital scan is a critical factor that might determine the scanning workflow procedures.