# Influence of Food Pigments and Thermal Aging on the Color Stability of Denture Base Resins
## 4 Discussion
Multiple comparisons revealed a similar trend across the various resin groups. Immersion of the specimens in red wine caused significantly higher changes compared to water (\(p<0.05\)) for all resins and compared to the carbonated soft drink (\(p<0.05\)) in the Rapid FN V4 and S V4 resins. Wine was the beverage that caused the greatest color changes, regardless of the resin type, was as has been presented in previous studies [2; 8; 12; 20; 23; 24]. Red wine contains darker pigments called chromogens (anthocyanins and derivatives) that adhere to the surface of dentures and promote discoloration over time [2]. Also have polyphenols, called tannins, that help the pigments bind to the proteins present in saliva, forming a tannin-protein complex that precipitates on the surface of resins and enamel, altering their color. Another aspect that favors the discoloration is that red wine is acidic, which makes the denture more porous, thus capturing more staining. Additionally, the presence of ethanol softens the resin surfaces, making them more susceptible to pigmentation [32]. The surface adsorption and absorption of pigments by the organic phases of acrylic resins can lead to alterations in their color [12; 24]. The fact that they are hydrophilic materials makes them more prone to absorbing pigments from beverages with which they come into contact. Some studies have shown that caramel, tannin acid, caffeine, and caffeic acid, which are present in coffee, may be responsible for the pigmentation shown in the present study [8; 13; 17; 20; 21; 23; 25; 26]. Coffee seems to maximally stain the resins due to tannic acid solutions allowing the yellow/brownish colorant in caffeine to be compatible with the polymer phase [24]. [PERSON] et al. [13] found that after 7 days of immersion in coffee, there was a reduction in luminosity and an increase in hue for the resins studied. Regarding the carbonated soft drink, in addition to being an acidic beverage, it contains phosphoric acid, which can affect the surface integrity of the material through erosion [22]. According to [PERSON] [16], its low pH increases the solubility of the resin, and as immersion time increases, water absorption becomes the main cause of discoloration. This explains the lower color change values of specimens immersed in this beverage compared to the others, which has also been seen in previous studies [2; 8; 13; 17; 22; 26]  
It is important to highlight that the control group also demonstrated color changes. As mentioned earlier, acrylic resins are hydrophilic materials, making water absorption the primary cause of the observed chromatic changes. The same finding was reported in the studies by [PERSON] et al. [24] and [PERSON] et al. [2]. For the present study, \(\Delta\)E values greater than 3.3 were considered clinically unacceptable [3; 7; 8; 22; 34], and \(\Delta\)E values between 1 and 3 were considered perceptible to the human eye [3; 35]. All specimens exhibited clinically acceptable values (\(\Delta\)E < 3.3). At T1, all color changes were perceptible to the human eye (\(\Delta\)E > 1), whereas at T2, only the color changes of specimens immersed in coffee and red wine were perceptible, regardless of resin type. The NBS units demonstrated that no specimen exhibited color changes above the \"perceptible\" level (between 1.5 and 3.0), meaning that, in a clinical scenario, these changes would be difficult for the patient to detect, as they would require a color alteration across the entire prosthesis surface. According to [PERSON] et al. [28], patients cannot detect chromatic changes below the \"slight\" level, that is, below 6 NBS units. Thus, the chromatic stability of the resins under study, after immersion in pigments from the beverages, was satisfactory, as it fell within clinically acceptable values and would hardly be detected by patients. Since pigments do not bind to the internal composition of resins; diffusion and degradation of the pigments can occur in the acrylic resin material.