## 4 Discussion  
This study utilized a clinical spectrophotometer employing the CIEDE2000 system, designed to rectify shortcomings of the CIE L*a*b* formula [20], to assess color changes in specimens. The CIEDE2000 formula improves upon the accuracy of the CIE L*a*b* formula in calculating color differences, thereby providing enhanced indications of perceptibility and acceptability [21]. In clinical dentistry, understanding color variations in objects heavily relies on visual perceptibility and acceptability threshold values. Color changes in this research were assessed based on acceptability (AT: \(\Delta\)E00 = 1.8) and perceptibility (PT: \(\Delta\)E00 = 0.8) thresholds, as documented by [PERSON] et al. [22]. Red wine, employed as a solution in this investigation, induces staining on resin composite due to its acidic nature; ethanol content; and pigmented compounds, such as anthocyanins and tannins [9]. The pH of red wine at the beginning was measured, and the value was 3.92. According to [PERSON] et al. (2017) [23], an immersion period of 24 h in vitro corresponds to approximately one month of clinical exposure. Thus, the 144-h immersion protocol used in our study is equivalent to around six months of clinical consumption. Alcohol in beverages like wine is believed to act as a plasticizer, softening the polymer matrix of resin composites, particularly in Bis-GMA and UDMA-based systems. This softening effect allows staining agents to penetrate more easily into the material. Studies have also shown that the alcoholic content in beverages like wine contributes to discoloration by further softening the resin matrix, making it more vulnerable to staining. This combination of matrix softening and the presence of colorants leads to increased staining in resin-based composites [9; 12]. Moreover, the presence of ethanol enhances the color alteration caused by anthocyanins and tannins, facilitating deeper penetration of these pigments into the resin composite [14; 24]. The discoloration of resin composite is influenced by factors such as filler size, silanization, and the type of monomers used [18; 25; 26]. Smaller fillers provide better surface smoothness and color consistency due to reduced surface roughness [25]. In this study, variations in color stability and surface roughness among different composites are likely related to filler size. The manufacturer reports that U and F have an average cluster particle size between 0.6 and 10 \(\upmu\)m, larger than G's 0.15 \(\upmu\)m. This size difference explains U's significantly higher color change compared to G, but it does not fully account for F's lesser discoloration, suggesting additional influencing factors. The silanization process plays a crucial role in reducing the discoloration of resin composites by improving the bond between filler particles and the resin matrix [11; 27]. G-aial Universal Injectable, using full silane coverage (FSC) technology, has fewer hydroxy groups on its glass fillers than conventional methods. This ensures uniform silane coverage, enhancing physical, chemical, and mechanical properties, including color stability. In this study, G-enial Universal Injectable shows significantly lower \(\Delta\)E than U but no statistical difference compared to F, indicating that other factors may also influence the outcome [26]. Hydrophilic monomers such as TEGDMA, Bis-GMA, and UDMA are known for their high water sorption rates, which directly influence the degree of discoloration in resin composites. TEGDMA, in particular, has the highest water sorption rate among these monomers, making it the most susceptible to color change. This is because TEGDMA's hydrophilic nature allows it to absorb more water and colorants, leading to significant discoloration over time [9; 18; 28; 29]. Bis-GMA and UDMA, while also hydrophilic, have slightly lower water sorption rates compared to TEGDMA. However, they still contribute to discoloration due to their ability to absorb water and colorants.