## 4 Discussion  
Taking into consideration the above mentioned, our study reveals significant differences in the degree of conversion between two dental resin brands, NextDent Orto Flex and Tera Harz TC-85, under varying UV exposure durations while printing. For the NextDent Orto Flex, the optimal polymerization time was found to be 7 s, as both shorter (5 and 6 s) and longer (8 s) exposures resulted in significantly lower DC. This decline in DC at non-optimal exposure times can be attributed to insufficient cross-linking at shorter durations and the potential degradation of the photoinitiators or polymer matrix at longer durations. These results align with previous findings that excessive UV exposure can degrade photoinitiators and cause oxygen inhibition, leading to incomplete polymerization [36; 37]. Conversely, Tera Harz TC 85 maintained relatively stable DC values around a 4 s exposure, with only the 2 s exposure showing a significant difference. This stability indicates that Tera Harz TC 85 has a more robust photoinitiation system that efficiently initiates polymerization even at shorter exposure times without detrimental overexposure effects. The higher overall DC rates for Tera Harz TC 85 compared to NextDent Orto Flex could be due to a more effective photoinitiator or a formulation that better resists the negative effects of UV overexposure, such as thermal degradation and oxygen inhibition [38; 39]. However, numerous strategies have been suggested in the literature to mitigate oxygen inhibition in photopolymerizations [37; 40; 41]: (1) increasing the light dose or intensity, (2) raising the photoinitiator concentration, (3) employing co-initiators, (4) adding radical scavengers, (5) conducting the process in an inert environment, and (6) utilizing chemical mechanisms such as thiol-ene and thiol-acrylate-Michael systems, which are less sensitive to oxygen. The differences in the degree of conversion and their response to UV exposure duration highlight the importance of optimizing curing parameters for different materials to achieve  
Figure 4: Glass transition temperature (\({}^{\circ}\)C). the best polymerization outcomes. These findings are consistent with the earlier studies that show that both the duration of UV exposure and the formulation of the photoinitiator system play crucial roles in determining the final mechanical and thermal properties of photopolymerized materials [42; 43]. The storage modulus (E\({}^{\prime}\)) is a critical parameter for evaluating the stiffness and rigidity of polymer-based dental resins, directly influencing their performance and durability in dental applications. NextDent generally exhibits higher E\({}^{\prime}\) values compared to Tera Harz, indicating that it forms a stiffer material. The presence of aromatic functional groups in NextDent, indicated by maxima at 754 cm\({}^{-1}\) and 693 cm\({}^{-1}\) (aromatic C-H wagging and the bending of the aromatic ring), indicates enhanced rigidity due to the planar structure and strong intermolecular interactions (\(\pi\)-\(\pi\) interactions) of these groups [44]. In contrast, Tera Harz TC 85 has significantly fewer aromatic groups, which may contribute to its lower rigidity and, consequently, a lower storage modulus. Additionally, the higher intensity of absorption bands at 980 cm\({}^{-1}\) and 847 cm\({}^{-1}\) in Tera Harz TC 85, attributed to C-H rocking and skeletal C-C stretching modes, indicates a more flexible polymer chain structure, potentially reducing the storage modulus. Shorter polymerization times (5 and 6 s) of NextDent Orto Flex result in significantly lower E\({}^{\prime}\) values compared to the 7 s control, likely due to incomplete polymerization and cross-linking. This indicates that adequate polymerization time is crucial for achieving optimal stiffness. Increasing the polymerization time to 8 s does not significantly enhance E\({}^{\prime}\) beyond the 7 s control, indicating a threshold beyond which additional curing does not further improve stiffness.