# Accuracy of 3D-Printed Master Cast Workflow Using a Digital Light Processing Primer
## Materials and Methods
\begin{table}
\begin{tabular}{l c} \hline \hline  & **Resin** \\ \hline Flexural strength [MPa] & \textgreater{}70 \\ \hline Elastic modulus [MPa] & \textgreater{}1500 \\ \hline Hardness [Shore D] & \textgreater{}80 \\ \hline Color & sand \\ \hline Curing wavelength [nm] & 385 \\ \hline \hline \multicolumn{3}{c}{**CAM Settings**} \\ \hline
**Printer** & \\ \hline DMD projector resolution [pixels] & \(1920\times 1024\) \\ \hline Spectral maximum of LED & 385 nm \\ \hline
**Membrane type of material unit** & flexible \\ \hline
**Support Structures** & \\ \hline Distribution & Based on object geometry \\ \hline Density & Medium \\ \hline Size & Medium \\ \hline Spherical support tip & Yes \\ \hline
**Cast** & \\ \hline Orientation strategy & Optimized quality \\ \hline
**Detail level (layer thickness [\(\mu\)m])** & Very high (50) \\ \hline Post processing & \\ \hline Washing solution & 99.9\% isopropyl alcohol \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Three-dimensional (3D) printing parameters settings. For local trueness evaluation of each preparation type (fixed dental prosthesis (FDP 17-15), inlay (24), and single crown (26)), the preparation surfaces were superimposed with the reference cast via local best-fit alignment (Figure 3). For FDP, only the surface of 17 was set as a reference for local best-fit alignment. [local_CON17-15,24,26], [local_PRINT17-15,24,26], and [local_IOS17-15,24,26] were measured against the reference file. Before point-to-surface measurement, the maximum tolerance was set to two millimeters and the surface comparison was applied on the test object. The values of the single distance measurements between two surfaces were exported as absolute values in American Standard Code for Information Interchange (ASCII) files. Each single data set of surface comparison contained approximately 300,000 point-to-surface measurements. For these values, a self-programmed python script for automated data evaluation was developed. This application allowed to run a data analysis under different prerequisites. For descriptive analysis, it was possible to include all deviation measurements or to exclude 1%, 5%, or 10% of the highest and lowest measurement values to avoid non-relevant outliers. In this study, all values were included and the absolute mean deviation, root mean square error (RMSE), median, standard deviation, and minimal and maximal distances were calculated. RMSE is defined as:  
\[\text{RMSE}=\sqrt{\frac{1}{n}\sum_{i=1}^{n}(\text{x}_{i}-\mu_{i})^{2}}\]  
where xi are the predicted values of the reference cast, \(\mu_{i}\) are the observed values of the test cast, and n is the number of observations. The RMSE describes the dispersion around a true value with respect to trueness and precision. Precision  
To analyze precision, the same alignment and superimposition procedure was applied, comparing the ILS scans of the ten gypsum casts [CON], the ILS scans of ten printed casts [PRINT], and the ten intraoral scans [IOS] among each other leading to 45 surface  
Figure 3: Local trueness evaluation via surface comparison: printed against reference: (a) [local_PRINT17-15;]; (b) [local_PRINT24]; (c) [local_PRINT26] [Scale \(\pm\) 50 \(\upmu\)m]. Figure 2: Principle of trimming of all test casts, best-fit alignment, and surface comparison: (a) reference cast; (b) test cast; (c) superimposition of reference and test cast; (d) surface comparison [Scale \(\pm\) 150 \(\upmu\)m]. comparisons each. The five ILS scans of the reference cast were compared with each other, too, leading to ten comparisons. Statistics  
SPSS 26 (IBM Corporation, Armonk, NY, USA) was used for statistical calculations. For full-arch trueness, the Shapiro-Wilk test revealed that the data of [REF]-[PRINT] and [REF]-[IOS] were not normally distributed. Therefore, the Mann-Whitney U test (two-tailed) was applied to test whether there was a statistically significant difference between [REF]-[CON] and [REF]-[PRINT] at \(p\leq 0.05\).