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Color Stability of Nanoparticles-Modified Dental Resin-Based Composites  
**[PERSON] 1,*-\(\copyright\), [PERSON] 1(\copyright\), [PERSON] 2, [PERSON] 3, [PERSON] 4(\copyright\) and [PERSON] 3,*-\(\copyright\)  
Footnote 24: [[https://www.mdpi](https://www.mdpi)]([https://www.mdpi](https://www.mdpi))Many previous studies have shown that immersion of light-cured composite restorative material in different beverages may cause varying degrees of staining. This variation depends mainly on their composition and properties, the concentration of staining agents, and the amount of exposure time [10; 11]. Several advancements were introduced to improve the properties of composite filling, including the incorporation of nanofillers, which enhance their mechanical, physical, and optical properties [12; 13]. The use of NPs can offer many advantages when they are incorporated into dental restorations; due to their decreased size, they provide a larger specific surface area that leads to unique characterization compared to bulk-size particles [3; 14]. However, NPs show an aggregation tendency that may interfere with the chemical interaction between these particles and the organic matrix. To overcome this drawback, a silane-coupling agent was used for the treatment of inorganic filler, leading to improved bond strength of the NPs and resin matrix and thus enhancing the properties of nanocomposite [15]. This enhancement encouraged the researchers to incorporate different NPs into dental biomaterials to improve their properties, including zirconium dioxide (ZrO\({}_{2}\)), titanium dioxide (TiO\({}_{2}\)), and silicon dioxide (SiO\({}_{2}\)) [16; 17; 18]. TiO\({}_{2}\) is favored in the dental field due to its superior properties, including corrosion resistance, high microhardness, adequate antimicrobial properties, and low cost. Moreover, the incorporation of TiO\({}_{2}\) into polymeric materials can enhance the mechanical, physical, and optical properties of the nanocomposite [19]. ZrO\({}_{2}\) is a white crystalline metal oxide that has widespread application in dentistry due to its biocompatibility, great strength, high wear resistance, and aesthetic acceptability; it has been used in many previous studies for the reinforcement of acrylic resin denture base materials and RBCs [12; 19]. Similarly, the tested SiO\({}_{2}\)-incorporated nanocomposites showed adequate resistance to abrasiveness and appropriate thermal stability. Prosthetically, the addition of SiO\({}_{2}\) nanoparticles to the acrylic resin denture base improved the wear resistance; additionally, it showed greater color stability after immersion in different beverage solutions [20; 21]. [PERSON] et al. and [PERSON] et al. found that the addition of NPs to dental restorations could improve their different properties, such as flexural strength, hardness, and wear resistance [12; 22]. The color stability of a restorative material greatly determines the success of dental fillings and patient acceptance [23]. NPs incorporating restorative materials presented improved optical properties when tested in previous studies. Because the NP dimension is less than the wavelength of visible light, the results showed an improved color appearance and enhanced light transmittance [24; 25]. Color measurement devices have been heavily used when testing dental materials to accurately assess their color changes. A spectrophotometer is considered an accurate and flexible measurement tool [26]. Compared to human eye observation, it can provide 33% increased accuracy and allow for higher objective matches in most of the cases tested [27]. A three-dimensional color space-based system was developed by the International Commission on Illumination (Commission Internationale de l'Eclairage; CIE) in 1976, and it consists of three axes. The L axis is a grayscale that represents the lightness, the a axis represents the red-green coordinates, and the b axis describes the blue-yellow coordinates.