# Effect of Different pH Beverages on the Color Stability of Smart Monochromatic Composite
## 3 Results
The possible reason for this color change is based on the fact that the acidic pH of Cola has the potential to erode the surface texture of the resin restoration and increase its water sorption, which eventually affects the affinity of the resin to extrinsic stains. Moreover, [PERSON] et al. [19] also observed that the Filtek Z250 was more stain-resistant than the Supreme composite after immersion in different beverages. In contrast, [PERSON] and [PERSON] [20] observed that despite having the lowest pH, Cola did not produce as much discoloration as coffee and milk tea. This observation may be due to the presence of yellow colorants in both coffee and tea, which have different polarities. Higher-polarity components, such as those present in milk tea, are eluted first, followed by the lower-polarity components present in coffee. Therefore, it is anticipated that discoloration by milk tea could be due to the adsorption of polar colorants onto the surface of the composite, whereas discoloration by coffee could be due to both the adsorption and absorption of colorants on the surface of the composite. This is further explained by the fact that the organic phase of the composite material allows for the penetration and absorption of colorants due to the polymer phase of the composite's affinity for the yellow colorants in the coffee [21]. Furthermore, [PERSON] et al. [22] also support the finding that coffee and tea produce more discoloration than cola or red wine. The resin component in composite plays a crucial role in staining susceptibility. Studies have shown that urethane di methacrylate is more stain-resistant compared to bis-GMA due to its low water solubility and absorption [19; 23]. Filtek Z250 contains three main components: bis-GMA, UDMA and bis-EMA. However, the TEGDMA (hydrophilic monomer) in Filtek Z250 was replaced with a blend of UDMA and bis-EMA, although it is still expected to absorb water; therefore, we observed highest \(\Delta\)E value in the FiltekZ250 coffee group. On the other hand, the major component of Omnichroma is urethane dimethacrylate (UDMA), which is hydrophobic in nature and may be attributed to the lowest \(\Delta\)E value, as observed in the Omnichroma milk tea group. The long-term color stability of the composite after restoration is an area of concern for many clinicians. Previously, studies have reported that the 24 h of tooth sample immersion in different beverages is equal to approximately one month in vivo [19]. However, this was expected at an oral temperature of 37 \({}^{\circ}\)C. The rise in temperature due to the hot beverages may expedite this process, so that temperatures higher than 51 \({}^{\circ}\)C are expected to simulate 12 months of in vivo environment compared to one-month in vitro at 37 \({}^{\circ}\)C [24]. Therefore, the 2 weeks of immersion in beverages in current study would correspond to an in vivo immersion of 14 months. In this study, color measurements were taken using a spectrophotometer. The perception of color is a psychophysical phenomenon with high chances of variation between persons or the same person at different times. The color measurements made by a spectrophotometer have eliminated the possibility of human errors. Studies have shown that the human eye cannot detect color changes with a color alteration value of less than 3.5 [18; 19]. In the present study, FT and OM showed color differences of more than 3.5, except for OM in the milk tea group. This indicates that the prolonged exposure of both the FT composite and OM composite are prone to staining by Pepsi and coffee. However, other chemical factors, such as the purity of the monomers and oligomers, initiators and inhibitors, type or concentration of activator, filler loading and color of the inorganic pigments, should also be considered [25]. The findings of this study must be seen in light of certain limitations. First, it is worth mentioning that this was an in vitro study, with inherent limitations when simulating an in vivo environment; therefore, the results should be interpreted cautiously.