## 3 Results  
### Degree of Conversion (DC)  
FTIR spectra of liquid (resin) and polymerized NextDent Ortho Flex and Graphy material are shown in Figure 1, while the spectra of Tera Harz TC-85 resin are described in detail in previous studies [11; 15]. The spectrum of the liquid sample of NextDent Ortho Flex material indicates a complex mixture of initial monomers, where the vibrational bands of methacrylate can be distinguished, which are more abundant compared to the spectrum of the liquid Tera Harz TC-85 material (Table 1). The presence of the carbonyl group is indicated by a stretching vibration at 1715 cm\({}^{-1}\), followed by a medium absorption with a maximum at 1650 cm\({}^{-1}\), which is contributed by the stretching vibration of the aliphatic C=C group visible as a slightly pronounced shoulder at 1638 cm\({}^{-1}\). The presence of an aliphatic C=C group is also proven by an additional band at 1617 cm\({}^{-1}\) as well as the sharp band of twisting vibrations at 810 cm\({}^{-1}\). Symmetric and antisymmetric deformationsand the stretching of methyl and methylene groups are visible as medium bands in the range -1500-1350 cm\({}^{-1}\) and -3000-2820 cm\({}^{-1}\), respectively. Below 1350 cm\({}^{-1}\), many strong C-C-O and C-O-C stretching vibrations can be seen. Absorption bands at 980 cm\({}^{-1}\) and 847 cm\({}^{-1}\) have been attributed to the C-H rocking and skeletal C-C stretching mode, while maxima at 754 cm\({}^{-1}\) (aromatic C-H wagging) and 693 cm\({}^{-1}\) (the bending of the aromatic ring) imply the presence of aromatic functional groups that are significantly smaller in the Tera Harz TC-85 material [34; 35]. The spectra also contain absorption features associated with N-H stretching (3343 cm\({}^{-1}\)) and bending vibrations (1522 cm\({}^{-1}\)) as a characteristic of urethane compounds. The differences in the FTIR spectra of the initial mixture and the polymerized material are primarily visible through the loss or diminishing of the bands mainly related to the C=C bonds (1617, 810 cm\({}^{-1}\)) and C-H and C-O bonds (1407, 1322, 1297 cm\({}^{-1}\), etc.) in the monomers, which can be used, more or less successfully, to monitor the extent of polymerization. In this paper, according to the previous study, the degree of conversion for both resin materials was determined by a peak at 810 cm\({}^{-1}\), originating from twisting vibrations of carbon-carbon methacrylate double bonds [11]. To enhance the resolution of the chosen band and \begin{table}
\begin{tabular}{l l} \hline \hline
**Wavenumber (cm\({}^{-1}\))** & **Vibration** \\ \hline
3343 & \(\
u\) N\({}_{-}\)H \\
2941 & \(\
u_{\rm ss}\) C\({}_{-}\)H (CH\({}_{2}\), CH\({}_{3}\)) \\
2859 & \(\
u_{\rm s}\) C\({}_{-}\)H (CH\({}_{2}\), CH\({}_{3}\)) \\
1715 & \(\
u\) C=O (ester) \\
1650 & \(\
u\) C=O (amide) \\
1638 & \(\
u\) C=C \\
1617 & \(\
u\) C=C \\
1522 & \(\delta\) N\({}_{-}\)H \\
1407 & \(\delta\) CH\({}_{2}\) \\ \(\sim\)1350–1000 & \(\
u\) C\({}_{-}\)C–O \\
980 & \(\delta_{\rm rc}\) C\({}_{-}\)H \\
847 & \(\
u\) C\({}_{-}\)C \\
810 & \(\delta_{\rm tw}\) C=C \\
754 & \(\delta_{\rm wg}\) C\({}_{-}\)H (aromatic) \\
693 & \(\delta\) aromatic ring \\ \hline \hline \end{tabular} Abbreviations: \(\
u\) = stretching, \(\delta\) = bending, \(\rm s\) = symmetric, as = asymmetric, rc = rocking, tw = twisting, and wg = wagging.  
\end{table} 
Table 1: FTIR peak identification for the NextDent Orto Flex resin. Figure 1: FTIR spectra (**A**) NextDent Orto Flex resin, (**B**) NextDent Orto Flex printed, (**C**) Tera Harz TC85 resin, and (**D**) Tera Harz TC85 printed. eliminate possible baseline shifts between samples, the Savitzky-Golay algorithm (second derivative with nine smoothing points) was applied. The DC is presented in Figure 2.  
The DC was analyzed for two brands, NextDent Orto Flex and Tera Harz TC 85, under varying durations of UV exposure. For NextDent Orto Flex, the DC values were significantly lower at 5 s (\(p\) = 0.003), 6 s (\(p\) < 0.001), and 8 s (\(p\) < 0.001) compared to the control at 7 s (Median = 97.55%).