## 4 Discussion
Through FT-IR, the characteristic vibrations of different groups within a material are identified, and the presence of additional substances is determined by interpreting the peaks in the obtained graph. Each component or bond structure exhibits its specific peak values, revealing interactions between different groups as wavelengths vary. In the realm of dental restorative materials, FT-IR spectra can detect carbon-carbon (C=C)-stretching vibrations both pre- and post-polymerization [29]. Additionally, the microhardness and monomer conversion values of restorative materials may reflect the efficacy of the polymerization process [32]. In addition, by utilizing the thermal properties of polymers, the extent of conversion from monomer to polymer and the amount of unreacted double bonds can be determined. The statistically significant difference among the restorative materials in terms of conversion rates, with Neo Spectra exhibiting the highest conversion, aligns with its superior mechanical performance observed in the microhardness analysis. The presence of aromatic and aliphatic double bonds in the monomers, as indicated by absorption bands at 1608 cm\({}^{-1}\) and 1638 cm\({}^{-1}\), respectively, underscores the complexity of polymerization reactions in dental composites. DSC analysis complements FT-IR by providing quantitative data on the degree of conversion and polymerization kinetics. Although the conversion rate of Omnichroma was higher than Myra, the absence of a statistically significant difference suggests similar curing efficiencies between these materials. This discrepancy with FT-IR results could be attributed to differences in the sensitivity and resolution of the two techniques, highlighting the importance of using complementary analytical methods for comprehensive material characterization. Moreover, the Tg value identified serves as a crucial parameter for polymer characterization, signifying a region of significant change in the polymer's physical properties. This value represents the temperature range at which the polymer transitions from a glassy state to a rubber-like material [14; 33]. Furthermore, indirect inference regarding monomer conversion can be made by comparing the microhardness measurements of the bottom/top surfaces, thereby establishing a correlation between the two values [34]. The process of ensuring thorough polymerization through irradiation leads to elevated microhardness values on the surfaces of resin materials [35]. This phenomenon arises from the high conversion rate of polymerization in resin-based materials, which is facilitated by a specific energy density [33]. However, the utilization of indirect methods such as microhardness may result in erroneous outcomes, as they do not directly determine the number of unreacted carbon double bonds [36]. Our findings suggest that polymerization appears to be quite effective based on the bottom/top microhardness values of the three dental composites. However, direct output from FT-IR and DSC methods contradictsthis observation. Essentially, our findings underscore the importance of not overlooking the potential margin of error in indirect methods. Merely assessing ratios should not be considered indicative of sufficient monomer conversion of resin-based materials. Each monomer possesses its own unique viscosity and flexibility, directly influencing the degree of conversion for dental composites [37]. While BIS-GMA exhibits a lower conversion rate compared to other monomers, TEGDMA has been found to have the highest conversion rate among monomers. Additionally, UDMA and BIS-EMA demonstrate better degree of conversion compared to BIS-GMA [38; 39]. Furthermore, the combination of TEGDMA and BIS-GMA increases the material's sensitivity to aqueous environments [40]. If a composite contains a nano content, it may affect BIS-GMA, thereby increasing the monomer conversion efficiency [41].