## 4 Discussion
The hydrophilic properties of the monomers that form the backbone of resin composites are different, and there is a close relationship between this property and the water absorption of the resin composite. The monomer with the most hydrophilic properties is TEGDMA. Bis-GMA monomer has been shown to have hydrophilic properties, although not as much as TEGDMA monomer. It has been reported that resin composites containing Bis-GMA show greater water absorption than resin composites containing UDMA and Bis-EMA [29]. On the other hand, the water absorption of UDMA monomer is lower than that of Bis-GMA and TEGDMA monomers. In addition to its low water absorption, its low solubility also results in less colouration of resin composites containing this monomer [2; 3]. Bis-EMA monomer has low water absorption due to the hydrophobic group in its structure. In light of this information, the lower mean \(\Delta\)E\({}_{00}\) values obtained with OM at both the T1 and T2 measurements may be due to the UDMA monomer it contains. However, the fact that higher \(\Delta\)E\({}_{00}\) values were obtained with this resin composite at T3 suggests that the degree of conversion as well as the monomer structure may influence the colour change. It has been reported that there is a relationship between the degree of conversion and the colour change in resin composites after polymerisation. Resin composites with a low degree of conversion exhibit poor colour properties due to residual monomers such as methacrylate remaining in their structures after polymerisation [29]. However, as the degree of conversion of the resin composites tested in the study was not investigated, further studies are required. When the effect of detox drinks on mean \(\Delta\)E\({}_{00}\) values was examined, it was found that there was a significant difference between detox drinks in terms of \(\Delta\)E\({}_{00}\) values in samples prepared with OM at all measurement periods; whereas, there was no significant difference between detox drinks in terms of mean \(\Delta\)E\({}_{00}\) values in samples prepared with OS. For samples prepared with FU and EU, it was found that there was no significant difference between detox drinks in terms of \(\Delta\)E\({}_{00}\) values only at T1. Based on these findings, it can be said that the structural properties of detox drinks play an important role in the effect of colour change in universal resin composites [23; 24]. A similar finding was reported in a study by [PERSON] et al., which evaluated the colour stability of single-shade composites after exposure to acidic beverages such as coffee, tea, and fruit juices [4]. The study observed progressively higher \(\Delta\)E\({}_{00}\) values in specimens immersed in pigmented acidic solutions, with a notable increase by day 30. These results support the idea that prolonged exposure to low-pH, chromogenic beverages can accelerate colour instability in resin-based materials. When the relationship between the exposure time of universal resin composites to detox drinks and colour change was examined, it was found that the highest colouration was obtained at T3 in all detox drinks in samples prepared with OM, OS, and EU. In samples prepared with FU, the highest \(\Delta\)E\({}_{00}\) values were obtained at T3 in the green and orange detox drinks, while it was obtained at T2 in the red detox drink. The different content and pH of the detox drinks may play a role in this finding. With resin composite restorations, especially in the anterior region, it is desirable that the colour remains stable and the translucency is similar to that of natural teeth [17; 30]. However, this is quite difficult to achieve, especially in Class III and Class IV restorations. In this study, the mean \(\Delta\)TP\({}_{00}\) values of the universal resin composites tested varied between 8.38 and 17.65.