## 2 Materials and Methods
Since errors may occur depending on the operator [27; 40], a single skilled operator (K.S.) performed all of the analyses. A CDM file was retrieved with the 3D inspection software, which was set to perform a 3D comparison of the inner surface of the crown. The inner surface of the crown was divided into four parts (marginal, axis, angular, and occlusal regions). The trueness of the inner surface of the crown may affect the marginal and internal fit, and many previous studies have evaluated the marginal and internal fit according to the region [2; 13; 14; 15; 16; 17; 18]. Therefore, the inner surface of the crown was divided into four parts to evaluate the trueness. The region up to 0.5 mm from the prosthesis margin was defined as the marginal region, the region starting at the end of the marginal region through the axis to the point where the curve starts was the axis region, the region starting from the end of the axis region \begin{table}
\begin{tabular}{c c c} \hline
**Lithium Disilicate Block** & **Material** & **Lot Number/Manufacturer** \\ \hline IPS e.max CAD (e.max) & Lithium disilicate glass ceramic & V36449/Ivoclar Vivadent \\ \hline Rosetta SM (HASS) & Lithium disilicate glass ceramic & ABD06 KE1502/HASS \\ \hline VITA Suprinity (VITA) & Zirconia-reinforced lithium silicate & 46191/VITA \\  & glass ceramic & \\ \hline \end{tabular}
\end{table} 
Table 1: Data for lithium disilicate blocks. Figure 2: Fabrication of scanned model. (**A**) Crowns fabricated from three types of lithium disilicate block; (**B**) contact scanning procedure. through the line angle to the point where the curve ends was the angular region, and the remaining region starting from the angular region was the occlusal region. After preparing a CDM file, a CSM file was retrieved, and the initial alignment was conducted with the best fit alignment. The inner region of the partitioned crown was appointed, and it was overlapped with the best fit alignment only in the point cloud of the appointed part. The sampling ratio was set to 100%. The dimensional difference between the CDM file and the CSM file was calculated for all data points of the partitioned inner region. The differences between all of the data points of the CDM and CSM were calculated from the closest data points to each other in all directions. At this time, the data points were calculated with the root mean square (RMS) value using the following formula:  
\[RMS=\frac{1}{\sqrt{n}}\cdot\sqrt{\sum_{i=1}^{n}(X_{1,i}-X_{2,i})^{2}}\]  
For all data points, \(X_{1,i}\) was the position of measurement point \(i\) in the reference scan data, and \(X_{2,i}\) was the position of measurement point \(i\) in the evaluation scan data. In addition, \(n\) refers to the total number of data points measured in each analysis. The RMS value indicates the degree of deviation of the scan data. A low RMS value indicates a good three-dimensional agreement of the overlapped data [27]. The CAM process aims to reproduce a modeled design and produce an accurate product. The tool target position may not be reached or exceeded, however, due to various factors affecting the cutting rate (e.g., the hardness of the material, the performance of the milling unit). Therefore, the 3D comparison is shown as a color difference map, with a range of \(\pm\)100 \(\upmu\)m (20 color segments) and an allowable tolerance range (green) of \(\pm\)10 \(\upmu\)m assigned. The red zone (10\(\sim\)100 \(\upmu\)m) shows that the CSM data are located above the CDM data, implying that the milling failed to reach the target position. In addition, the blue zone (\(-\)10 to \(-\)100 \(\upmu\)m) shows that the CSM data are located below the CDM data, implying that the milling exceeded the target position. The green zone (\(\pm\)10 \(\upmu\)m) corresponds to the areas that were machined very accurately. All of the data were analyzed using SPSS statistical software (IBM SPSS Statistics v23.0, IBM Corp, USA). First, through an application of the Shapiro-Wilk test, the normal distribution of the data was investigated.