## 2 Materials and Methods  
Table 1 summarizes all material details used to conduct the current study. Disc-shaped specimens were prepared according to ISO 4049:2000 that were 7 \(\times\) 2 \(\pm\) 0.03 mm in diameter and thickness, respectively [29]. To reduce variability, all specimens were fabricated by the same examiner. Two hundred RBC specimens (\(n\) = 10, 70/beverage) were fabricated based on a sample size calculated using the necessary values from previous studies [20; 21; 30]. According to NP types, specimens were divided into four groups: three modified groups--ZrO(Zr), TiO\({}_{2}\) (Ti), and SiO\({}_{2}\) (Si); and one that remained unmodified as a control group (N0). According to NP concentrations (3 wt.% and 7 wt.%), these three groups were further subdivided into two subgroups (Zr3, Zr7, Ti3, Ti7, Si3, and Si7) for a total of six tested experimental groups. The selected nanoparticles (ZrO\({}_{2}\), TiO\({}_{2}\), and SiO\({}_{2}\)) were treated separately using a silane coupling agent [3-trimethoxysil-propyl-methacrylate (TMSPM)] (Shanghai Richem International Co., Ltd., Shanghai, China) to generate reactive groups on their surfaces for better adhesion between the NPs and resin matrix. The amount of silane coupling agent (X) required for efficient and uniform coverage of the nanoparticles was calculated by the following equation [15]:  
\[\mathrm{X}=(\mathrm{A}/\omega)\ f\]  
where A is the surface area of the nanoparticles (m\({}^{2}\)/g), \(\omega\) is the surface coverage per gram of silane MPS (\(\omega\) = 2525 m\({}^{2}\)/g), and \(f\) is the number of nanoparticles (g). The TMSPM was dissolved in acetone to ensure that it would evenly coat the surface of the NPs; then, the NPs were collected in the TMSPM-acetone solution and stirred with a magnetic stirrer for 60 min. A rotary evaporator (Rotavapor(r) R-300, Buchi AG, Flawil, Switzerland) was used to eliminate the solvent under a vacuum for 30 min at 60 \({}^{\circ}\)C and 150 rpm. As the mixture dried, it was heated at 120 \({}^{\circ}\)C for 2 h and then bench cooled to room temperature to obtain surface-treated nanoparticles [31; 32; 33]. An electronic scale of 0.001 g in accuracy was used to weigh and incorporate two concentrations (3 wt.% and 7 wt.%) of RBCs. Regarding the nanocomposite formulation, a glass beaker with a 7 mm-diameter glass rod was used to mix the NP powder into a composite resin material for 5 min at room temperature to form a homogeneous mix expressed as a constant color. Subsequently, the homogenous mix was packed into a Teflon split mold with the exact dimensions (7 \(\times\) 2 mm) and then covered by Mylar strips prior to light curing [14; 34]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Brand Name/Manufacturer** & **Company Name** & **Specifications** \\ \hline \multirow{2}{*}{Nexcomp} & META BIOMED, Cheongju-si, & Resin: Bis-GMA, Bis-EMA, UDMA, TEGDMA. \\  & Republic of Korea & Fillers: 0.04–0.7 μm barium aluminum boro-silicate. \\  & & Light cured, A2 \\ \hline \multirow{2}{*}{ZrO\({}_{2}\) nanoparticles} & & Spherical, white, and tetragonal nanoparticles \\  & & (12 \(\pm\) 3 nm; purity \(>\) 99\%) \\ \hline \multirow{2}{*}{TiO\({}_{2}\) nanoparticles} & NanoGATE, 6 October, Giza, Egypt & Spherical, white, and anatase nanoparticles \\  & & (15 \(\pm\) 3 nm; purity \(>\) 99\%) \\ \hline \multirow{2}{*}{SiO\({}_{2}\) nanoparticles} & & Spherical, white, and amorphous nanoparticles \\  & & (21 \(\pm\) 3 nm; purity \(>\) 99\%) \\ \hline \multirow{2}{*}{Silane-coupling-agent} & Sigma/Aldrich Chemie GmbH, & 3-trimethoxysilyl propyl methacrylate (TMSPM). \\  & Taufficren, Germany & Purity 98\%, ethanol 99.7\%., lot No. 440159 \\ \hline \multirow{6}{*}{ZrO\({}_{2}\): zirconium dioxide; TiO\({}_{2}\): titanium dioxide; SiO\({}_{2}\): silicon dioxide; Bis-GMA: bisphenol A glycidyl methacrylate; Bis-EMA: bisphenol A ethoxylated dimethacrylate; UDMA: urethane dimethacrylate; and TEGDMA: triethylene glycol dimethacrylate.}