## 2 Materials and Methods  
### Surface Preparation of Samples  
The biomaterial under study was a dental Wirobond(r) C cobalt-chrome metal-to-ceramic alloy (BEGO Bremer Goldschlagerei Wilh. Herbst GmbH & Co. KG, Bremen, Germany), which complies with ISO 22674 [19] and ISO 9693-1 [20] standards. Wirobond(r) C is produced in accordance with the ISO 13485 standard [21] and is approved as a class IIa medical device. This alloy is commercially used for the fabrication of prosthetic restorations, or sections thereof, with thin cross-sections exposed to very high loads, e.g., removable partial dentures, clasps, veneered crowns, long-span bridgework or bridges with small cross-sections, bars, retainers, and implant-supported superstructures (Figure 1).  
The Wirobond(r) alloy does not contain nickel, cadmium, beryllium, or lead. It is primarily intended for patients allergic to nickel. Cerium in its chemical composition ensures a high bond strength with the ceramic, minimizing the risk of subsequent flaking or chipping. This cobalt-based dental casting alloy does not cause a chemical reaction in the patient's mouth. It does not require oxidation. It is characterized by simple processing and casting, as well as its carbon-free composition (making its especially suitable for laser welding), high adhesion to ceramics, and low heat conductivity (ensuring pulp protection and high wearing comfort for the patient) (Table 1). The Wirobond(r) alloy is biocompatible, corrosion-resistant (thanks to a firmly adhering passive layer), and can easily be laser-welded. It is as flexible as precious metals. No cytotoxic potential was determined, in accordance with the ISO 10993-5 standard [25].  
The Wirobond(r) C dental alloy was provided in the form of cylinders, from which disc-shaped samples were cut with thicknesses of 3 mm. The samples were included in graphite using an ATM Opal 400 hot mounting press (Spectrographic Ltd., Guiseley, Leeds, UK) at a pressure of 3.5 bars at 180 \({}^{\circ}\)C for 10 min. The included samples were ground using the metallographic grinding and polishing machine Metkon Forcipol 102 (Metkon Instruments Inc., Bursa, Turkey) on P320-P2500 abrasive papers (Buehler Ltd., Lake Bluff, IL, USA) and were polished using colloidal SiO\({}_{2}\) suspension (0.04 \(\upmu\)m grain size, Struers, Cleveland, OH, USA). The polished samples were degreased in acetone (Avantor Performance Materials Poland S.A., Gliwice, Poland) for 20 min using an ultrasonic cleaner USC-TH (VWR International, PA, USA), and then sonicated in ultrapure water (Milli-Q Advantage A10 Water Purification System, Millipore SAS, Molsheim, France) for 20 min.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Value** \\ \hline Type (accord. to ISO 22674) & 4 \\ Density & 8.5 g cm\({}^{-3}\) \\ Preheating temperature & 900–1000 \({}^{\circ}\)C \\ Solidus and liquidus temperature & 1360 \({}^{\circ}\)C, 1420 \({}^{\circ}\)C \\ Casting temperature & 1500 \({}^{\circ}\)C \\ Young’s modulus & 180 GPa \\ Proof strength (R\({}_{\text{p0,2}}\)) & 440 MPa \\ Ultimate strength (Rm) & 780 MPa \\ Elongation after fracture & 16\% \\ Vickers hardness & 310 HV10 \\ Coefficient of thermal expansion (CTE) & 14.3 \\
25–500 \({}^{\circ}\)C, 10\({}^{-6}\) K\({}^{-1}\) & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Wirobond® C dental alloy characteristics.  
Figure 1: Wirobond® C dental alloy. (**a**) Ref [22]; (**b**) the alloy used in the dental and prosthetic office for partial dentures [23]; (**c**) the trading condition of the alloy (available as cylinders) [24].