## 4 Results  
The transmittance data, before and after aging, recorded at 400 nm and 700 nm by the spectrophotometer (Table 1) (chosen as the limits of the measurement range) were used to create average curves for each aligner produced with the three 3D printers and the two thermoforming disks considered in this study (Figures 4 and 5). The pre- and post-aging transmittance curves show that more constant transparency was maintained with Zendura FLX material than with Scheu Ca Pro + material, for all three printers compared. At T0, Scheu CA Pro+ aligners printed with Prodways LD20 have a higher transmittance (T%) than the other analyzed, with values of 88.169 \(\pm\) 0.65 and 89.581 \(\pm\) 0.91, at 400 and 700 nm, respectively. At T1, the same material and printer showed a high-significance change (_p_ < 0.001) with transmittance values of 84.171 \(\pm\) 0.29 and 87.345 \(\pm\) 0.80, at the respective wavelengths. (Figure 6) \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Aligner**} & \multicolumn{5}{c}{**Trasmittance at 400 nm (\(\pm\) SD)**} & \multicolumn{5}{c}{**Trasmittance at 700 nm (\(\pm\) SD)**} \\ \cline{2-9}  & **As Received** & **After Aging** & _p-Value_ & **\% Variation** & **As Received** & **After Aging** & _p-Value_ & **\% Variation** \\ \hline
**CA-ze** & \(85.492\pm 2.67\) & \(84.985\pm 0.65\) & \(0.604\). & \(-0.6\) & \(88.309\pm 2.21\) & \(87.009\pm 0.54\) & \(0.119\) & \(-1.5\) \\ \hline
**CA-scCA** & \(87.367\pm 0.63\) & \(80.404\pm 2.95\) & \(<\)0.001 & \(-8.0\) & \(88.965\pm 0.62\) & \(84.516\pm 2.28\) & \(0.003\) & \(-5.0\) \\ \hline
**PR-ze** & \(85.643\pm 1.90\) & \(85.837\pm 1.12\) & \(0.799\). & \(0.2\) & \(88.408\pm 1.67\) & \(88.029\pm 1.20\) & \(0.592\) & \(-0.4\) \\ \hline
**PR-scCA** & \(88.169\pm 0.65\) & \(84.171\pm 0.29\) & \(<\)0.001 & \(-4.5\) & \(89.581\pm 0.91\) & \(87.345\pm 0.80\) & \(<\)0.001 & \(-2.5\) \\ \hline
**RS-ze** & \(82.312\pm 1.17\) & \(81.075\pm 2.67\) & \(0.238\). & \(-1.5\) & \(85.408\pm 1.00\) & \(83.545\pm 1.77\) & \(0.018\) & \(-2.2\) \\ \hline
**RS-scCA** & \(87.587\pm 1.34\) & \(79.878\pm 0.49\) & \(<\)0.001 & \(-8.8\) & \(88.853\pm 1.29\) & \(84.304\pm 0.76\) & \(<\)0.001 & \(-5.1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Transmittance values of six type of aligners before and after in vitro aging. The data are the average of nine values \(\pm\) SD. High significance level (_p_ < 0.001). Figure 3: The 18 aligner after aging. Figure 4: Transmittance curves of all aligners at T0 without SD for better visual clarity. Figure 5: Transmittance curves of all aligners at T1 without SD for better visual clarity. Transparency decreased after aging even with Carbon L1 and RapidShape D100+ printers and Scheu CA Pro+ material. (Figures 7 and 8). The highest percentage variation was reported by the RapidShape D100+ printer with Sheu CA Pro+ of \(-8.8\) and \(-5.1\), respectively, recording a significant loss of transparency. This printer with this material had mean values of 87.587 \(\pm\) 1.34 and 88.853 \(\pm\) 1.29 before aging and 79.878 \(\pm\) 0.49 and 84.304 \(\pm\) 0.76 after aging. On the other hand, non-significant variation (\(p\) > 0.01) is found with the Zendura FLX material for the three printers considered in the study. Prodways LD20 printer with this second material presented transmittance values, at 400 nm and 700 nm, of 85.643 \(\pm\) 1.90 and 88.408 \(\pm\) 1.67 at T0 and 85.837 \(\pm\) 1.12 and 88.029 \(\pm\) 1.20 at T1. Figure 6: Comparison of transmittance values of the Scheu CA Pro + with Prodways LD20.printer before and after aging. The curves are the average of nine spectrophotometry measurements \(\pm\) SD. Figure 7: Comparison of transmittance values of the Scheu CA Pro + with Carbon L1 printer before and after aging. The curves are the average of nine spectrophotometry measurements \(\pm\) SD. When it comes to comparing the same printer with the two different materials, it is clear that the transmittance curves are more constant with Zendura FLX.