## 2 Materials and Methods  
### Specim Preparation  
The G*Power software program v3.1.3 (Heinrich Heine University, Dusseldorf, Germany) was used to calculate the sample size. The calculation was conducted based on an effect size of 0.4, a 90% power probability, and a 0.05 significance level, and it was determined that 10 specimens per group were required. In line with this, a total of 160 flat-shaped specimens (10 mm length, 10 mm width, and 2 mm thickness) were fabricated from four different materials using two distinct CAD/CAM production processes, milling and 3D printing, intended for use as definitive restoration materials, as shown in Figures 1 and 2. The milling blocks utilized in this study included LU (Lava(tm) Ultimate) and GR (Grandio(tm)), while the 3D-printed resins comprised CT (Crowntec(tm) and CB (C&B Permanent(tm)), as presented in Table 1.  
As shown in Figure 2, the flat specimens from milling blocks were fabricated by sectioning the blocks under water cooling using a low-speed precision cutting machine equipped with a precision diamond saw (IsoMet 1000; Buehler, Waukegan Road Lake Bluff, IL, USA). On the other hand, flat specimens from 3D-printed resins were prepared using an open-source LCD 3D printer (Sonic Mighty 4K; Phrozen, Hsinchu, Taiwan). The \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Material Type**} & \multicolumn{2}{c}{**Composition**} & \multirow{2}{*}{**Manufacturer**} \\ \cline{3-4}  & & & **Filler** & & **Polymer** \\ \hline \multirow{3}{*}{Lava Ultimate(TM) (LU)} & \multirow{3}{*}{\begin{tabular}{c} Milling block \\ nanoceramic composite \\ resin \\ \end{tabular} } & 80 wt.\% fillers of silica (size 20 nm), zirconia (size 4–11 nm) & 20 wt. \% Bis-GMA, UDMA, Bis-EMA, TEGDMA & 3M\({}^{\text{TM}}\) ESPE, St. Paul, MN, USA \\ \hline \multirow{3}{*}{Grandio(TM) (GR)} & \multirow{3}{*}{\begin{tabular}{c} Milling block \\ nanohybrid composite \\ resin \\ \end{tabular} } & 86 wt.\% nanohybrid fillers (particle size 20–60 nm) & 14 wt.\% UDMA, DMA & \begin{tabular}{c} VOCO GmbH, \\ Cuxhaven, Germany \\ \end{tabular} \\ \hline \multirow{3}{*}{Crowntec(TM) (CT)} & \multirow{3}{*}{3D-printed composite resin} & 30–50 wt.\% fillers (particle size 0.7 μm) & \begin{tabular}{c} SEterification products \\ of 4,4\({}^{\prime}\)- \\ isopropyldiphenol, \\ ethoxylated and \\ 2-methylprop-2 enoic \\ acid \\ \end{tabular} } & \begin{tabular}{c} Saemco Dental AG, \\ Rebstein, Switzerland \\ \end{tabular} \\ \cline{3-4}  & & & \begin{tabular}{c} Diurethane \\ dimethacrylate, \\ 2-Propenoic acid, \\ 2-methyl-, \\ (1-methylylidene) \\ bis \\ \end{tabular} & \begin{tabular}{c} ODS, Seoul, Republic \\ of Korea \\ \end{tabular} \\ \cline{3-4}  & & & \
\begin{tabular}{c} ODS, Seoul, Republic \\ of Korea \\ \end{tabular} \\ \cline{3-4}  & & &
\begin{tabular}{c} SEter, 2-HEMA, \\ diphenyl (2,4,6- \\ trimethylbenzoyl) \\ phosphine oxide, and \\ additives \\ \end{tabular} \\ \hline \hline \end{tabular} Abbreviations: BisGMA, bisphenol-A-glycidyldimethacrylate; UDMA, urethane dimethacrylate; BisEMA, ethylated bisphenol A dimethacrylate; BisEMA, ethylated bisphenol A dimethacrylate; TEGDMA, triethylenediydclimethacrylate; DMA, dimethacrylate.  
\end{table} 
Table 1: Data on CAD/CAM milling blocks and 3D-printed composite resins used in this study. Figure 2: Schematic diagram illustrating the workflow employed to produce specimens in the present study, using either the milling process or 3D printing. design of the specimens was created using freely available software on [[https://www.tinkercad.com](https://www.tinkercad.com)]([https://www.tinkercad.com](https://www.tinkercad.com)). The design files were then exported as STL files and imported into Preform Software Chitubox v.1.9.1 (Phrozen, Hsinchu, Taiwan) for slicing. To ensure uniformity, the specimens were duplicated and standardized by positioning them on supports at a 90\({}^{\circ}\) angle during the printing process.