## 4 Discussion  
In the present study, the color matching ability of the single-shade resin composite (OM) was compared to the conventional resin composite (FT). Furthermore, the color stability (staining resistance) of the both materials (OM and FT) after cola and coffee immersion was investigated. The outcomes revealed a significantly better color matching ability for conventional resin (FT) for shades B1 and A3 compared to OM resin. However, the color matching ability in shades B2 and C3 for FT and OM resins was comparable. In addition, OM showed lower color stability (stain resistance) in cola and comparable color stability to the conventional composite in coffee. Therefore, the hypothesis was rejected. A plethora of explanations could be proposed for the outcomes observed regarding color matching and stability. OM is considered a smart material with ideal properties to reflect similar shades to those of the surrounding teeth [18]. This material is colorless and the color properties are based on the structural color. According to the current literature, OM comprises a 260 nm spherical filler, which generates a and b color coordinates that are necessary to match natural teeth [18]. [PERSON] et al. has suggested that the changes in the filler size and composition greatly influence the material's color stability and optical properties [19]. In the present study, the OM filler consisted only of specific, single-sized spherical particles, which enhanced the light reflection within a specific wavelength inside the tooth color space. Therefore, the claims of OM having better control of the optical properties of the material are supported by previous evidence [19]. Moreover, the tooth factor is another variable that influences the color matching ability of the restorative material [19]. The literature states the tooth color depends on the dentin color rather than the enamel color [20]. In previous studies [19; 20], enamel showed limited influence on the final shade of dental restorations; however, [PERSON] et al. [6] and [PERSON] et al. [4] suggested that enamel has a strong influence on color perception in terms of lightness. Moreover, the changes in enamel and dentin for each tooth also greatly influence the efficiency of the restorative material's color stability [11]. In the present study, the authors performed an experiment on acrylic teeth to establish standardization. Denture teeth were used to standardize the color measurements, as it is impossible to standardize the color of natural teeth; however, resin teeth have highly glossed and smooth surfaces (highly polished), which affects color assessments. Researchers believe that a material's composition greatly influences its optical properties and color matching effects [21]. Among the commonly used material, Filtek presented the highest degree of resistance against discoloration [21]. The hydrophobic nature of Filtek resin causes decreased water sorption, solubility, and diffusion coefficient due to the presence of silorane [22]. The absence of the Bis GMA monomer reduces the hydrophilicity of the material, thereby reducing the risk of saliva absorption, which affects the material  
Figure 3: Color stability testing: Filtek specimens after immersion in cola (**A**) and coffee (**B**); OM specimens after immersion in cola (**C**) and coffee (**D**). over a long period. A similar outcome was found in a present study that showed Filtek to have better color stability compared to OM. Recent studies analyzing the color matching ability of OM have suggested the color matching to be 60.8% [23]. The present study showed similar outcomes, with variable \(\Delta\)E values for OM, the greatest color differences for shade B1, and the smallest differences in shade C3. The possible explanation for the vast differences is the colorless filler powder that strongly reflects light, which enhances the shade's appearance compared to the surrounding structure. However, this structural color phenomenon cannot be displayed on white backgrounds [23].