2.4. Statistical Analyses

Statistical analyses were conducted using SPSS (IBM Statistics, v.25.0; IBM Corp, Armonk, NY, USA), and significance level was set at 0.05. Normal distribution of all data was examined through the Shapiro–Wilk test and homogeneity of variance with Levene’s test. As a result, the deviation values in 2D planes and inTOL (%) for precision between the 3D printer groups were analyzed using one-way ANOVA and Tukey HSD test as post hoc (significance level at p < 0.05), while differences of RMS values and inTOL (%) for trueness at 4 landmark 3D areas between printers were analyzed using Kruskal–Wallis H test. The Mann–Whitney U-test and Bonferroni correction were used for post-testing (p < 0.05/3 = 0.017).

The Intraclass Correlation Coefficient (ICC) value is the reliability calculated by the raters’ measurements. The ICC means reproducibility if the test is repeated several times [21]. The ICC value was also used to show the level of precision, at 95% confidence interval in this study.