## 3 Results  
There was a significant difference in the trueness of the inner surface of the crown according to the type of lithium disilicate block (\(p<\) 0.001; Figure 3; Table 2). There was no significant difference between e.max (27.7 \(\pm\) 2.9 \(\upmu\)m) and HASS (28.0 \(\pm\) 3.4 \(\upmu\)m) in the marginal region (\(p\) = 1.0), while the trueness was at a minimum for VITA (20.7 \(\pm\) 6.6 \(\upmu\)m) (\(p<\) 0.001). In addition, the values for the axis, angular, and occlusal regions were the highest for e.max, and there was no significant difference between HASS and VITA (\(p>\) 0.05). The overall RMS value was at a maximum (42.9 \(\pm\) 4.4 \(\upmu\)m) for e.max, followed by HASS (30.1 \(\pm\) 9.0 \(\upmu\)m) and then VITA (27.3 \(\pm\) 7.9 \(\upmu\)m). However, there was no significant difference between HASS and VITA (\(p\) = 0.541).  
There was a significant difference between all of the regions for the inner surface of the crown (\(p<0.001\); Table 2). The angular region on the inner surface of the crown exhibited a significantly higher trueness (\(p<0.005\)). There was no significant difference in the marginal, angular, or occlusal regions, except for in the e.max group (\(p>0.05\)).  
Figures 4 and 5 show the color difference map of the 3D analysis. In the angular region, the red zone is predominant, meaning that the milling failed to reach the target position. In the marginal region, the green color is most common, indicating that the milling was performed accurately. In the axis and occlusal regions, several color zones appear to equal degrees. The green zone appears the least with e.max. Furthermore, in the angular and occlusal regions, the range of the red zone is greatest.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **e.max** & **HASS** & **VITA** & \(p\) \\ \hline
**Crown Inner Region** & & **RMS (\(\mu\)m), Mean \(\pm\) SD** & & \\ \hline Margin & \(27.7\pm 2.9^{\text{Aa}}\) & \(28.0\pm 3.4^{\text{Aa}}\) & \(20.7\pm 6.6^{\text{Ab}}\) & \textless{0.001 *} \\ \hline Axis & \(42.6\pm 6.5^{\text{Ba}}\) & \(26.6\pm 11.1^{\text{Ab}}\) & \(27.1\pm 10.4^{\text{Ab}}\) & \textless{0.001 *} \\ \hline Angular & \(71.4\pm 6.3^{\text{Ca}}\) & \(46.8\pm 14.5^{\text{Bb}}\) & \(38.1\pm 7.5^{\text{Bb}}\) & \textless{0.001 *} \\ \hline Occlusal & \(37.2\pm 4.2^{\text{Ba}}\) & \(30.3\pm 5.9^{\text{Ab}}\) & \(22.8\pm 4.0^{\text{Ac}}\) & \textless{0.001 *} \\ \hline \(p\) & \textless{0.001 *} & \textless{0.001 *} & \textless{0.001 *} & \\ \hline Overall RMS value & \(42.9\pm 4.4^{\text{a}}\) & \(30.1\pm 9.0^{\text{b}}\) & \(27.3\pm 7.9^{\text{b}}\) & \textless{0.001 *} \\ \hline \hline \end{tabular} RMS: root mean square. Significance was determined by the * Kruskal–Wallis test: \(p<0.05\). The letters indicate significant differences revealed by the Mann–Whitney \(U\)-test and the Bonferroni correction method. The upper- and lower-case letters indicate the differences in the crown inner region (row) and block type (column), respectively.  
\end{table}
Table 2: Comparison of RMS values for different lithium disilicate blocks and crown inner regions.  
Figure 3: Comparison of RMS values for each crown inner region for different lithium disilicate blocks.