# Accuracy of 3D-Printed Master Cast Workflow Using a Digital Light Processing Primer
## 4 Discussion
Other studies reported a mean trueness deviation of 97 \(\upmu\)m (SD \(\pm\) 73 \(\upmu\)m) and RMSE values of 105.5 \(\upmu\)m (SD \(\pm\) 22,5 \(\upmu\)m), 27 \(\upmu\)m (SD \(\pm\) 7 \(\upmu\)m) and 28.09 (SD \(\pm\) 2.11 \(\upmu\)m) [1,30,31,32]. For SLA, [PERSON] et al. showed RMSE values of 85.2 \(\upmu\)m (SD \(\pm\) 13.1 \(\upmu\)m) [32]. [PERSON] et al. reported median trueness values of 146.6 \(\upmu\)m for FFF and 125.2 for photopolymer jetting [33]. CLIP was shown in recent literature with a trueness of 48 \(\upmu\)m (SD \(\pm\) 44 \(\upmu\)m) [30]. The full-arch precision results based on mean deviation of 32 \(\upmu\)m (SD \(\pm\) 10 \(\upmu\)m) were competitive, too. [PERSON] et al. stated a precision of 53.8 \(\upmu\)m (SD \(\pm\) 22.5 \(\upmu\)m) [32]. The analysis of the single steps, [REF]-[IOS], [IOS]-[PRINT], and [REF]-[PRINT], revealed that the widening of the arch in the molar area, whilst performing intraoral scans, was partially compensated by a relative compression of the arch by the printing process. Figure 5 shows this observation exemplarily. On the condition that the deviations in the different working steps took place in the same area which was confirmed by the color maps, the compensation theory can be justified as follows: [REF]-[IOS] showed an absolute mean deviation of 19 \(\upmu\)m. Based on the intraoral scan, [IOS]-[PRINT] differed by 38 \(\upmu\)m. For [REF]-[PRINT], deviations in the same direction resulted in the sum of [REF]-[IOS] and [IOS]-[PRINT] (19 \(\upmu\)m + 38 \(\upmu\)m). In this study, [REF]-[PRINT] displayed an absolute mean deviation value of 33 \(\upmu\)m which was below the sum value (19 \(\upmu\)m + 38 \(\upmu\)m) and additionally below the deviations of [IOS]-[PRINT]. This indicates that the deviations acted in opposite directions (widening and compression) and consequently compensated each other. The compression after printing can be explained by a potential shrinkage of the printed object during polymerization. The local RMSE deviations of [local_PRINT] were 35 \(\upmu\)m (SD \(\pm\) 9 \(\upmu\)m) for the FDP preparation, 18 \(\upmu\)m (SD \(\pm\) 5 \(\upmu\)m) for the single crown, and 19 \(\upmu\)m (SD \(\pm\) 3 \(\upmu\)m) for the inlay preparation. Other authors using a DLP printer achieved RMSE trueness values of 51.39 \(\upmu\)m (SD \(\pm\) 3.37 \(\upmu\)m) for FDP preparations, 46.93 \(\upmu\)m (SD \(\pm\) 2.28 \(\upmu\)m) for crown preparations, and 46.0 \(\upmu\)m (SD \(\pm\) 1.58 \(\upmu\)m) for inlay preparations [1]. [PERSON] et al. described RMSE values of 66.9 (SD \(\pm\) 20.9) for inlay, 84.3 (SD \(\pm\) 22.5) for single crowns, and 117.3 \(\upmu\)m (SD \(\pm\) 38.5) for FDP [32]. Therefore, the results of the present study were comparable or lower than the findings in recent literature. Trueness RMSE values reported for SLA were 60.7 \(\upmu\)m (SD \(\pm\) 12.1 \(\upmu\)m) for inlays, 62.0 \(\upmu\)m (SD \(\pm\) 10.6 \(\upmu\)m) for single crowns, and 81.5 \(\upmu\)m (SD \(\pm\) 14.1 \(\upmu\)m) for FDP [32]. [PERSON] et al. reported RMSE values of 22 (SD \(\pm\) 5) for the internal area [31]. The local accuracy values of the FDP preparation obtained from [local_CON] and from [local_PRINT] did not differ significantly, whereas the values of the inlay preparation and the single crown preparation of the [local_PRINT] were more than twice lower than the [local_CON] trueness. In the case of the inlay and crown preparation, the standard deviations for [local_CON] were more than five times higher than those for [local_PRINT]. The RMSE values amplified these observations. The high [local_CON] trueness values of the inlay and single crown preparation could be explained by high retention forces that were necessary when removing the impression from the reference cast. These applied high forces may have led to an irreversible distortion of the polyvinyl siloxane. It could be  
Figure 5: Compensation of the arch widening during the entire workflow: (**a**) [REF]-[IOS] (grey = REF; red = IOS).