## 4 Discussions  
This study compared four models obtained with a DLP printing system with four SLA printed models. The measurements were obtained via extra-oral scanning. The average accuracy (precision and bias) of the two printing methods were compared. As the data were not normally distributed, non-parametric tests were performed. The results of the comparison show that models printed with SLA (printer A) had a lower precision in the mesiodistal and buccolingual directions but similar precision in the other measured features (tooth height, arch curvature and interdental distances). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Kolmogorov–Smirnov**} & \multicolumn{3}{c}{**Shapiro–Wilk**} \\  & & **Variable** & **Statistic** & **df** & \(p\)**-Value** & **Statistic** & **df** & \(p\)**-Value** \\ \hline \multirow{4}{*}{Precision (RMS)} & \multirow{2}{*}{SLA} & Height of the tooth & 0.192 & 16 & 0.119 & 0.876 & 16 & 0.034 \\  & & Mesial–distal dist. & 0.205 & 16 & 0.071 & 0.893 & 16 & 0.062 \\  & & Buccal–lingual dist. & 0.096 & 41 & 0.200 & 0.969 & 41 & 0.329 \\ \cline{2-10}  & & Height of the tooth & 0.184 & 16 & 0.15 & 0.938 & 16 & 0.32 \\  & & Mesial–distal dist. & 0.183 & 16 & 0.158 & 0.855 & 16 & 0.016 \\  & & Buccal–lingual dist. & 0.11 & 40 & 0.200 & 0.944 & 40 & 0.047 \\ \hline \multirow{4}{*}{Bias} & \multirow{2}{*}{SLA} & Height of the tooth & 0.16 & 16 & 0.200 & 0.918 & 16 & 0.159 \\  & & Mesial–distal dist. & 0.104 & 16 & 0.200 & 0.956 & 16 & 0.587 \\  & & Buccal–lingual dist. & 0.11 & 41 & 0.200 & 0.961 & 41 & 0.166 \\ \cline{2-10}  & & Height of the tooth & 0.152 & 16 & 0.200 & 0.965 & 16 & 0.749 \\  & & Mesial–distal dist. & 0.156 & 16 & 0.200 & 0.881 & 16 & 0.041 \\  & & Buccal–lingual dist. & 0.1 & 40 & 0.200 & 0.931 & 40 & 0.017 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Normality tests for the data of the analyzed features. The models manufactured with the DLP method showed, on the other hand, significantly higher bias for tooth height and mesial-distal direction. This indicates that although some methods may be more precise than others, other factors (e.g., parameter setting, model orientation along the printing axes) can influence the accuracy of the resulting models. Although models printed with DLP were more precise in certain directions, the models also showed deviations from the target values (bias). A set of advantages that digital models offer are their ease of use for educational, diagnostic and therapeutic purposes. Digital models also have another advantage of providing much better tactile and visual information. There are only a few studies that establish a clinically acceptable range of errors for such measurements. For clinical accuracy, the acceptable range was considered 0.20 to 0.55 mm [15]. The conclusion of our measurements based on previous study recommendations indicate that the printing models produced by DLP and SLA printers are clinically acceptable. The results indicate that the models can be viable options for various clinical applications. In the digital dental workflow, discrepancies can be built in at every step. It is important to fully define the main characteristics evaluated in this study. The finest feature a 3D printer can reproduce is called resolution. This depends on the technology used and the printer. The three axes x, y and z are used to define the resolution (in \(\upmu\)m). It is common to consider the layer thickness to be measured on the z axis [21]. The characteristic that represents how close two printed objects are to each other is called accuracy. Another measure that is important is the trueness. It measures the discrepancy between the desired dimensions of the object and the actual measurements [18]. The discrepancies depend also on the type of material chosen, the material activation range and its wavelength and even on the total exposure during the manufacturing of the model. Sometimes you have incompatibility between the printer and the material.