## 3 Results  
One-way ANOVA results of the RMS values of each surface are presented in Table 1, and Figure 6 illustrates the RMS at each measured surface for control and different layer-thickness groups. Figure 5: Margins according to the grading system ((**A**): Grade 3; (**B**): Grade 2; (**C**): Grade 1). Significant differences were observed among fabrication techniques for intaglio and intaglio occlusal surface RMS values (\(p\leq 0.026\)). Milled crowns presented significantly lower RMS values than 100 \(\upmu\)m crowns at both intaglio (\(p\) = 0.025, estimated difference in means: \(-\)20.2 \(\upmu\)m) and intaglio occlusal (\(p\) = 0.021, estimated difference in means: \(-\)10 \(\upmu\)m) surfaces. Every other pairwise comparison for intaglio (\(p\geq 0.251\)) and intaglio occlusal (\(p\geq 0.178\)) surfaces were nonsignificant. Average margin quality of the crowns showed significant differences (Figure 7); based on the 3-point scale, milled crowns presented higher quality than the others (\(p\) < 0.001 vs. 20 \(\upmu\)m, estimated difference in means: 1.25 points; \(p\) = 0.001 vs. 50 \(\upmu\)m, estimated difference in means: 0.68 points; and \(p\) < 0.001 vs. 100 \(\upmu\)m, estimated difference in means: 1.53 points). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Layer Thickness** & **Overall RMS (\(\upmu\)m)** & **External RMS (\(\upmu\)m)** & **Intaglio RMS (\(\upmu\)m)** & **Marginal RMS (\(\upmu\)m)** & **Intaglio Oclusal RMS (\(\upmu\)m)** \\ \hline Control (Milled) & 64.5 \(\pm\)10.94 \({}^{\text{a}}\) & 54 \(\pm\)21.29 \({}^{\text{a}}\) & 32.6 \(\pm\)15.01 \({}^{\text{a}}\) & 11.3 \(\pm\)14.36 \({}^{\text{a}}\) & 31.5 \(\pm\)6.92 \({}^{\text{a}}\) \\
20 \(\upmu\)m & 56.1 \(\pm\)10.7 \({}^{\text{a}}\) & 59.4 \(\pm\)10.7 \({}^{\text{a}}\) & 49.9 \(\pm\)12.13 \({}^{\text{ab}}\) & 14.9 \(\pm\)9.57 \({}^{\text{a}}\) & 33.4 \(\pm\) 2.22 \({}^{\text{ab}}\) \\
50 \(\upmu\)m & 53.3 \(\pm\)9.3 \({}^{\text{a}}\) & 48.5 \(\pm\)13.67 \({}^{\text{a}}\) & 45.4 \(\pm\)15.75 \({}^{\text{ab}}\) & 9.1 \(\pm\)8.02 \({}^{\text{a}}\) & 34.7 \(\pm\)1.83 \({}^{\text{ab}}\) \\
100 \(\upmu\)m & 61.3 \(\pm\)15.31 \({}^{\text{a}}\) & 62.4 \(\pm\)18.21 \({}^{\text{a}}\) & 52.8 \(\pm\)17.32 \({}^{\text{b}}\) & 14.6 \(\pm\)9.94 \({}^{\text{a}}\) & 41.5 \(\pm\)12.55 \({}^{\text{b}}\) \\ \hline \hline \(p\) values & 0.145 & 0.263 & 0.026 & 0.576 & 0.024 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean RMS (\(\upmu\)m) values \(\pm\) standard deviations for milled and 3D-printed interim crowns. Different superscript lowercase letters in same column indicate significant differences among groups (\(p\) < 0.05). Figure 6: Box-plot graph of the RMS values of milled and 3D-printed interim crowns according to different surfaces. The margin quality of 50 \(\upmu\)m crowns was higher than that of 20 \(\upmu\)m (\(p\) = 0.006, estimated difference in means: 0.58 points) and 100 \(\upmu\)m (\(p\) < 0.001, estimated difference in means: 0.85 points) crowns. The difference between 20 \(\upmu\)m crowns and 100 \(\upmu\)m crowns was nonsignificant (\(p\) = 0.348). Table 2 summarizes the \(p\) values when the Tukey HSD test was applied to analyze the effect of margin location on the margin quality within each fabrication technique. No significant differences were found between the quality of the margins at different locations for 20 \(\upmu\)m (\(p\)\(\geq\) 0.121) and 50 \(\upmu\)m (\(p\)\(\geq\) 0.765) crowns. However, margin quality of milled (\(p\) = 0.002) and 100 \(\upmu\)m (\(p\) < 0.001) crowns were significantly affected by the margin location. The mesial, distal, and lingual margin quality of the milled crowns was similar (\(p\)\(\geq\) 0.885), while buccal margin quality was inferior to that at other locations (\(p\)\(\leq\) 0.03). For the 100 \(\upmu\)m crowns, lingual margin quality was higher compared with other locations (\(p\) < 0.001); the differences among other locations were nonsignificant (\(p\)\(\geq\) 0.831).