# Accuracy of 3D-Printed Master Cast Workflow Using a Digital Light Processing Primer
## 4 Discussion
These optical properties were important to provide realistic optical conditions for the optical impression system. [PERSON] et al. described that highly translucent materials can affect the accuracy [28]. They stated that materials such as lithium disilicate can decrease trueness and precision [28]. For Primescan, scanning lithium disilicate with a medium translucency and a Vita color A2 showed the highest mean deviation for both trueness (23 \(\upmu\)m \(\pm\) 3 \(\upmu\)m) and precision (33 \(\upmu\)m \(\pm\) 4 \(\upmu\)m) compared to fourteen other groups (e.g., composites, metals, dentin, enamel, etc.) [28]. The lowest mean deviation was obtained for polished amalgam with a trueness of 11 \(\upmu\)m and a precision of 16 \(\upmu\)m [28]. Due to the small differences between the lowest and highest trueness values, the influence of the material properties must be relativized. Although glazed lithium disilicate teeth were used in this study, the scans showed a good accuracy. Other authors using the same type of scanner based on the principle of parallel confocal microscopy achieved a full-arch trueness of about 30 \(\upmu\)m [23,29]. [PERSON] et al. obtained trueness values of 33.9 \(\upmu\)m (SD \(\pm\) 7.8 \(\upmu\)m) for the (90-10)/2 percentile [23]. [PERSON] et al. found mean deviation values of 33.8 \(\upmu\)m (SD \(\pm\) 31.5 \(\upmu\)m) [29]. However, all authors used software versions, which were below the version which was used in the present study (v5.2.2 RC1). Local mean trueness values of [local_IOS] ranged from 7 \(\upmu\)m (SD \(\pm\) 6 \(\upmu\)m) to 11 \(\upmu\)m (SD \(\pm\) 2 \(\upmu\)m). RMSE values were between 9 \(\upmu\)m (SD \(\pm\) 7 \(\upmu\)m) and 15 \(\upmu\)m (SD \(\pm\) 4 \(\upmu\)m). These minor differences between absolute mean deviation and RMSE values underlined the small spread of the deviation values. [PERSON] et al. reported a local accuracy of 18.7 \(\upmu\)m (SD \(\pm\) 2.8 \(\upmu\)m) using the (95-5)/2 percentile [27]. Within the digital workflow, the digital data sets which were produced with the intraoral scanner [IOS] were transferred into real casts by DLP printing. For evaluating the accuracy of the printer, this step is decisive. The lower the deviation between the digital data set and the corresponding cast the better the accuracy of the printer. This aspect was evaluated in the present study by digitizing the printed casts with an industrial scanner and comparing these data sets [PRINT] with their corresponding digital data sets obtained from the intraoral scanner [IOS]. The absolute mean deviation in this working step was 38 \(\upmu\)m. The standard deviation was 6 \(\upmu\)m, the range of deviation values was between 28 \(\upmu\)m (minimum) and 49 \(\upmu\)m (maximum), the median value was 38 \(\upmu\)m, and the root mean square error was 58 \(\upmu\)m. In particular, the latter value indicates the low variation of the printed objects. For clinical relevance, the deviation of the printed object from the original situation is of major importance. Full-arch accuracy is essential for the fitting process of CAD/CAM generated prosthetic restorations to assess occlusal contacts and dynamic contacts in articulated casts. Full-arch accuracy is also important to check proximal contacts of dental restorations or for the manual veneering of metal-based or ceramic frameworks. Local accuracy focuses on the preparation itself, neglecting adjacent teeth; therefore, the significance of proximal contacts is not considered. For fitting of multi-unit fixed partial dentures, full-arch accuracy is mandatory, too. Furthermore, the full-arch accuracy analysis is necessary to define overall distortions. In the present workflow, the digital workflow showed an absolute mean trueness of 33 \(\upmu\)m (SD \(\pm\) 4 \(\upmu\)m) and an RMSE trueness of 48 \(\upmu\)m (SD \(\pm\) 6 \(\upmu\)m).