## 4 Discussion  
The aim of this study was to test whether there was a statistically significant difference between occlusal devices printed for the same jaw but of different height and volume. The results revealed that the null hypothesis had to be rejected. The volume measurements showed that there was a minimal shrinkage of the printed object in relation to the reference data file. In relation to their reference files, for the more voluminous [4.5_TOTAL], a volume difference of approximately 2.11% and for of approximately 2.35% was measured. This may lead to the conclusion that the polymerization shrinkage of the resin during printing was not completely compensated. The comparison of the trueness values of the [2.5_TOTAL] and the [2.5_INTERNAL] and of the [4.5_TOTAL] and the [4.5_INTERNAL] revealed only minor differences. The low precision values of all four data sets [2.5_TOTAL], [2.5_INTERNAL], [4.5_TOTAL], and [4.5_INTERNAL] confirmed a good reproducibility referring to absolute deviations. With respect to precision, the maximum difference between the absolute deviations and the RMSE values was 16 \(\upmu\)m. These small differences underline the good reproducibility as RMSE squares all deviations, because the RMSE is more sensitive to outliers. For [2.5_INTERNAL] the mean trueness was 59 \(\upmu\)m (SD \(\pm\) 5 \(\upmu\)m). [PERSON] et al. revealed mean positive deviations around +174 \(\upmu\)m [SD \(\pm\) 66 \(\upmu\)m] and mean negative deviations \begin{table}
\begin{tabular}{c c} \hline
**[2.5_TOTAL]** & **Volume [mm\({}^{3}\)]** \\ \hline Reference file & 5682.69 \\ \hline Printed (mean) (N = 10) & 5548.93 \\ \hline Absolute Volume Difference & 133.76 \\ \hline Relative Volume Difference & 2.35\% \\ \hline
**[4.5_TOTAL]** & **Volume [mm\({}^{3}\)]** \\ \hline Reference file & 6737.55 \\ \hline Printed (mean) (N = 10) & 6595.38 \\ \hline Absolute Volume Difference & 142.17 \\ \hline Relative Volume Difference & 2.11\% \\ \hline \end{tabular}
\end{table} 
Table 6: Absolute and relative volume differences between reference and prints. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multicolumn{2}{c}{**n**} & \multicolumn{2}{c}{**Precision Based on Absolute Deviation [\(\upmu\)m]**} & \multicolumn{4}{c}{**Precision Based on RMS Error [\(\upmu\)m]**} \\ \hline  & & **Minimum** & **Maximum** & **Mean \(\pm\)** & **Mean \(\pm\)** & **Mean \(\pm\)** & **Mean \(\pm\)** & **Mean \(\pm\)** & **Mean \(\pm\)** & **Mean \(\pm\)** & **Mean \(\pm\)** \\  & & & **Detailation** & **Median** & **Maximum** & **Maximum** & **Median** & **Detailation** & **Median** \\ \hline
[2.5\_TOTAL] & 10 & 6 & 29 & \(19\pm 10\) & 26 & 21 & 46 & \(34\pm 8\) & 37 \\ \hline
[4.5\_TOTAL] & 10 & 7 & 45 & \(26\pm 13\) & 25 & 23 & 65 & \(42\pm 12\) & 41 \\ \hline \end{tabular}
\end{table} 
Table 5: Precision [2.5_TOTAL] and [4.5_TOTAL]. around \(-135\) um [SD \(\pm\) 60 um] using a DLP printer for occlusal devices with a material thickness of 1. mm [42]. In comparison, SLA technology showed mean positive deviations of +105 um [SD \(\pm\) 18 um] and mean negative deviations of \(-85\) um [SD \(\pm\) 15 um] [42].The present study exhibited lower results; [2.5_INTERNAL] showed a mean absolute deviation of 59 um, while the DLP printer results described above would lead to mean deviation of 154.5 um ((174 + 135)/2). The [4.5_INTERNAL] showed better results with an absolute mean trueness of 80 um as well. The [2.5_INTERNAL] also achieved better trueness in contrast to the SLA printer which exhibited a mean absolute deviation of 95 um ((105 + 85)/2). [PERSON] et al. evaluated the accuracy of the intaglio surfaces of printed occlusal devices (material thickness: 2 mm) which were horizontally and vertically positioned on the building platform [17].