## 3 Results and Discussion
### DC Analysis  
The DC of UTBCs due to photo-irradiation was assessed using FTIR. The peak area of the aliphatic curable vinyl group at about 1638 cm\({}^{-1}\) (A\({}_{1638}\)) was compared with that of the internal standard aromatic C=C peak (A\({}_{1608}\)) before and after light curing (Equation (1)). The results of DC measurements were reported as the average and standard deviation (SD) of four independent replicates of each resin composite (Figure 4 and Table 2). The DC was higher for composites containing dCl-BisGMA than for the reference dCl-BisGMA-free  
Figure 3: Storage modulus (G’, solid markers) and loss modulus (G”, open markers) of UTBC resin composites at 25 \({}^{\circ}\)C.  
one. However, the difference was statistically insignificant. The slight increases in DC of dCl-BisGMA to 79.01% for UTBC100, compared with 74.18% of UTBC0, is likely due to the lower viscosity of dCl-BisGMA, allowing better mobility of the particles (molecules and radicals) and thus facilitating higher conversion. Generally, incomplete vinylic DC is due to rapid solidification and gelation that may hamper radical mobility. Since the experimental conditions are the same, and dCl-BisGMA has a structure similar to that of BisGMA, except for the secondary hydroxyl groups, the altered properties of UTBC100 could be attributed to the absence of \(-\)OH and the presence of \(-\)Cl. Furthermore, dCl-BisGMA allows enhancement of the hydrophobicity characteristic and thus reduced the intermolecular interaction, leading to lower viscosity compared to BisGMA. According to literature [30; 31; 32], many factors can influence the DC of composites, including resin matrix composition, filler type and geometry, and their ratios and curing conditions. The effect of filler loading and degree of salinization on the DC has also been investigated [30], reporting lower conversion with increasing filler percentage but no visible differences between the DC of silane treated and untreated fillers, whereas DC decreases with silane amount increase. Compared with filled composites, the DC of the unfilled resin matrix is higher due to mobility restriction caused by fillers [33]. This negative impact of filler on the DC is independent of whether or not the filler was silanized [30]. In this regard, the DC of unfilled composites containing dCl-BisGMA was found to increase with dCl-BisGMA amount increase [2]. For instance, the DC of resins containing 70 wt% of BisGMA or dCl-BisGMA (and 30 wt% TECDMA) were 62.0 and 70.6%, respectively, which is reasonably due to the lower viscosity of dCl-BisGMA, compared with that of BisGMA. In this study, the DC of UTBCs was in the range of 74.18-79.01% and increased with dCl-BisGMA amount increased. However, the apparent higher values of DC of UTBCs are due to the high amount used of diluents TECDMA and UDMA (50% and 30% with respect to the total resin weight, respectively). Generally, the percentage of DC for adequate clinical performance has not yet been determined [34]. Nevertheless, for both filled and unfilled dCl-BisGMA-based composites, the obtained DC was above the minimum acceptable values for clinical use (>55%) [35]. The DC of dental composite commonly varies between 40% and 75% [36]; however, other ranges were also reported [37; 38] with higher values closer to 85% [39]. The difference in the DC of various systems can be due to several reasons, including the variation in composition, viscosity, curing conditions, curing times, etc. In this work, the resin matrix of UTBC0 consists of conventional monomers (TEGDMA, TEGDMA, and BisGMA) commonly used in dental composites. Thus, this dCl-BisGMA-free composite was used as a control during the evaluation of the tested properties of dCl-BisGMA containing composites (UTBC25-UTBC100).