## 2 Materials and Methods  
Four different resin-modified CAD/CAM ceramic materials, Lava Ultimate Restorative, Vita Enamic, Cerasmart, and Crystal Ultra, were evaluated. The tested materials are detailed in Table 1.  
CAD/CAM blocks were milled into 12 mm cylindrical blocks using a milling device (Ceramill Motion 2, [PERSON], Koblach, Austria). Next, the cylindrical blocks were sectioned (IsoMet 1000, Buehler, Bluff, IL, USA) to obtain a 1.2 mm disc shaped under water cooling. Forty-eight specimens (12 \(\times\) 1.2 mm\({}^{2}\)) were prepared from each material (LU, VE, CS, and CU). The specimen size was calculated using a free ware (G*Power v. 3.1.9.7 for windows, Heinrich-Heine-Universitat, Dusseldorf, Germany) based on the 0.8 power, 0.032 effect size, and 0.05 significance level. The prepared specimens were polished with increasing grit sizes (300-1200 grit) of silicon carbide papers (Waterproof SiC Paper; Struers) at 300 rpm with water coolant for 30 s by a single operator (M.H.) in order to standardize and establish a baseline roughness profile for all the groups [39]. A digital micrometer (Digimatic Micrometer; Mitutoyo) was used to confirm the specimen thickness, and any specimen that did not fit the required specifications was replaced. All the specimens underwent ultrasonic cleaning (Quantrex, L and R Manufacturing, Inc., Kearny, NJ, USA) in distilled water for 10 min, followed by 40 s of air drying [40]. Afterwards, the specimens were roughened with a fine 30 um grit diamond rotary bur (Komet, Rock Hill, SC, USA) under running water for 30 s in a single direction [41; 42] to simulate the clinical adjustment of a dental prosthetic crown. Then, the specimens were randomly allocated into four subgroups (n = 12) using simple randomization (Research Randomized, v.4; [[http://www.randomizer.org/](http://www.randomizer.org/)]([http://www.randomizer.org/](http://www.randomizer.org/)), accessed on 12 June 2022). One group (n = 12) was designated as the control for each material and did not receive any surface treatment. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **Shade/Code** & **Manufacturer** & **Composition** \\ \hline \begin{tabular}{c} Lava \\ Ultimate \\ Restorative \\ \end{tabular} & A2-HT/LU & 3M ESPE, St. Paul, MN, USA & Matrix: BisGMA, BisEMA, TEGDMA, and UDMA (20 wt.\%) \\ \begin{tabular}{c} Ultimate \\ Restorative \\ \end{tabular} & A2-HT/LU & 3M ESPE, St. Paul, MN, USA & Fillers: zirconia nanoparticles, silica, and silica/zirconia nanoclusters (80 wt.\%) \\ \hline \begin{tabular}{c} Vita Enamic \\ \end{tabular} & 2M2-HT/EN & \begin{tabular}{c} Vita Zahnfabrik, H. Rauter \\ GmbH \& Co, Bad Säckingen, \\ Germany \\ \end{tabular} & \begin{tabular}{c} Feldspathic ceramic containing aluminum oxide \\ (86 wt.\%) infiltrated by cross-linked polymers of \\ BisGMA and UDMA (14 wt.\%) \\ \end{tabular} \\ \hline Cerasmart & A2-HT/CS & GC America, Alsip, IL, USA & Matrix: BisMEPP, UDMA, and DMA (29 wt.\%) \\ \begin{tabular}{c} Crystal Ultra \\ \end{tabular} & A2-C block/CU & Digital Dental, Scottsdale, AZ, USA & \
\begin{tabular}{c} Ceramic-like inorganic silicate glass fillers (70 wt.\%) \\ infiltrated by cross-linked polymers of BisGMA, UDMA, and BUDMA) (30 wt.\%) \\ \end{tabular} \\ \hline
\begin{tabular}{c} BisGMA, Bisphenol-A-glycidyldimethacrylate; BisEMA, Ethoxylated bisphenol A dimethacrylate; TEGDMA, Triethyleneglycdimethacrylate; UDMA, Urethane Dimethacrylate; BisMEPP, Bispenol A bis (2-hydroxyethyl ether) dimethacrylate; DMA, Dimethacrylate; BUDMA, 1, 4-butanediol dimethacrylate. \\ \end{tabular} \\ \hline \end{tabular}
\end{table} 
Table 1: Resin-modified CAD/CAM ceramic materials. The experimental groups were surface treated using different protocols in accordance with the respective manufacturer's recommendations. The MP group was polished using a Luster Meisinger polishing kit (Hager and Meisinger GmbH, Neuss, Germany) comprising diamond-impregnated rubber polishers designed for resin-modified ceramics.