# Accuracy of 3D-Printed Master Cast Workflow Using a Digital Light Processing Primer
## 4 Discussion  
In the present study, the absolute mean deviations of the [REF]-[PRINT] revealed significantly better results compared with [REF]-[CON]. Therefore, the null hypothesis had to be rejected for the full-arch values. In the present study, the absolute mean deviation was 69 \(\upmu\)m (SD \(\pm\) 24 \(\upmu\)m) and the RMSE was 119 \(\upmu\)m (SD \(\pm\) 29 \(\upmu\)m) for the conventional workflow represented by gypsum casts. Since the deviations are squared in RMSE, high outliers were considered with a higher impact. Other studies revealed absolute mean deviations around 16.2 \(\upmu\)m (SD \(\pm\) 14.5 \(\upmu\)m) and 15 \(\upmu\)m (SD \(\pm\) 4 \(\upmu\)m) [21, 22]. Absolute median values of 16.3 \(\upmu\)m (SD \(\pm\) 2.8 \(\upmu\)m) and an RMSE of 28.49 \(\upmu\)m (SD \(\pm\) 1.74 \(\upmu\)m) were reported [1, 23]. One explanation for the higher deviation values observed in the present study may be that the reference model exhibited pronounced interdental undercuts. [PERSON] et al. stated that interdental areas in periodontally compromised dentitions are better displayed in intraoral scans than conventionally [24]. Furthermore, the crown lengths might exceed the heights of the crowns used in other studies. The anterior segment was relatively protruded. Although massive undercuts were partially blocked with wax, these properties may have resulted in higher withdrawal forces when removing the impression trays. As a result, there was a risk of deformation of the impression material. In that case, this phenomenon should have happened unnoticed since the quality of the impression was checked thoroughly to detect visible defects and to ensure a stable connection to the tray. In comparable studies, polyvinyl siloxane was used as established conventional impression material [1, 21, 25]. The study setup was tested thoroughly to get used to the material and to check the test environment. Before the main experiment was performed the workflow was tested by thirty impressions. The manufacturer's instructions were kept in all aspects for impression taking and further processing. The full-arch accuracy of the conventional workflow [REF]-[CON] and of the digital printer workflow [REF]-[PRINT] was evaluated by surface deviation measurement [23, 26]. To avoid unnecessary outliers during registration and deviation measurements, the digital data sets and the reference data set were identically trimmed at the borders and at the proximal areas. Additionally, all outlier measurements >2.00 mm were discarded before the calculation of deviations to avoid the inclusion of obvious artifacts. In other studies, the 20/80 quantile, the 10/90 percentile, and the 5/95 quantile were used due to the assumption that values beyond these thresholds were irrelevant artifacts [17, 23, 26, 27]. In the present study, 1/99, 5/95, and 10/90 ranges would have excluded relevant values (Figure 4). According to the authors' knowledge, this was the first study that evaluated the digital workflow by comparing the different steps with each other. The first step within the digital workflow was to achieve a digital data set from the reference cast using an intraoral scanner. The full-arch mean trueness value of these scans [REF]-[IOS] was 19 \(\upmu\)m (SD \(\pm\) 3 \(\upmu\)m). The  
Figure 4: Excluded areas depending on the included quantiles [Scale \(\pm\) 150 \(\upmu\)m]: (a) 10/90 quantile (highlighted area = excluded); (b) 5/95 quantile (highlighted area = excluded); (c) 1/99 (highlighted area = excluded). precision based on absolute mean deviation was 15 \(\upmu\)m (SD \(\pm\) 4 \(\upmu\)m). A study of the same working group found a full-arch accuracy of 29 \(\upmu\)m (SD \(\pm\) 3 \(\upmu\)m) using the same intraoral scanner but with an older software version (v5.1) [26]. In the former study, machined zirconia tooth surfaces were captured. To imitate tooth-like optical properties, the teeth of the present study were made of lithium disilicate with glazed surfaces. Only the prepared surfaces were left as machined.