## 3 Materials and Methods  
### Materials and Sample Preparation  
A total of 10 identical square plates were fabricated using SLM. The dimensions of the plates were 5 \(\times\) 5 mm, with a thickness of 0.3 mm. These dimensions were chosen so that the samples would fit into the diffractometerray and would correspond to the clinical requirements for the metallic substructure thickness of a metal-ceramic crown. The design was defined using the exocad basic (Darmstadt, Germany) software. Remanium star CL Co-Cr-W alloy (powder), Type 5 (Dentaurum, Ispringen, Germany) was used for the SLM fabrication of metal plates. The nominal chemical composition of the alloy is given in Table 1[45]. The Mlab 200R SLM (GE Additive, West Chester, PA, USA) machine was used for the fabrication of the metal plates. The Mlab 200R SLM machine uses a laser system of 200 W, with a scanning speed of 7 m/s and a focus diameter of approximately 75 \(\upmu\)m. The printing process takes place under inert gas, shielded from external influences. The printing planes are perpendicular to the SLM building direction. \begin{table}
\begin{tabular}{c c} \hline \hline
**Component** & **(wt \%)** \\ \hline Co & 60.5 \\ Cr & 28 \\ W & 9 \\ Si & 1.5 \\ Other elements \(<\) 1\%: Mn, N, Nb, Fe; free from Ni, Be, and Ga \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of remainium star CL Co-Cr-W alloy (as given by the manufacturer). After finishing the printing procedure, the plates were removed from the printing tray using a micromotor disc and were then sandblasted using a sandblasting machine standard for dental use. Subsequently, each of the 10 plates was subjected to ceramic veneering, as described in Tables 2 and 3. To ensure the flatness of the samples, the ceramics were layered while keeping the same thickness of 1.5 mm, which matches the clinical requirements. Two different feldspathic ceramics from two different manufacturers (P1 and P2), with different firing parameters, were used for veneering the Co-Cr-W alloy plates. IPS InLine (Ivoclar, Schaan, Liechtenstein) Basic Kit was used for 5 plates (P1) and the Baot Metal Ceramic Standard Kit (Baot, China) for the other 5 plates (P2). Only one side of the samples was layered with ceramic (denoted as C), while the other side was left unlayered, consisting of as-3D-printed Co-Cr-W dental alloy (denoted as M). The firing parameters used were chosen according to the manufacturer's instructions (Tables 2 and 3). The veneering and the firing were carried out by the same dental technician (C.S.). Each of the samples was placed in the center of the ceramic furnace. The chemical composition of IPS InLine (Ivoclar, Schaan, Liechtenstein), the ceramic layers of Dentin, Enamel (Transpa), Glaze, and Opaquer (according to the manufacturer), is given in Table 4 and is described as consisting of a glassy matrix and leucite crystals [46]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample Number** & **Ceramic Layers Deposited on** & **Number of Firings and Firing Parameters for** \\  & **the C Side** & **Each Ceramic Layer** \\ \hline
1\_Co-Cr-W\_alloy & As-3D-printed & No firing \\
2\_P1\_C & Opaquer & First firing at 930 \({}^{\circ}\)C for 13 min \\
3\_P1\_C & Opaquer + Dentin & First firing at 930 \({}^{\circ}\)C for 13 min and \\  & & second firing at 910 \({}^{\circ}\)C for 15 min \\  & & First firing at 930 \({}^{\circ}\)C for 13 min, second firing at \\
4\_P1\_C & Opaquer + Dentin + Enamel & 910 \({}^{\circ}\)C for 14 min \\  & & First firing at 930 \({}^{\circ}\)C for 13 min, second firing at \\
5\_P1\_C & Opaquer + Dentin + Enamel + Glaze & 910 \({}^{\circ}\)C for \\  & & 15 min, third firing at 900 \({}^{\circ}\)C for 14 min, and \\  & & fourth firing at 800 \({}^{\circ}\)C for 15 min \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Ceramic firing parameters of the P1 samples.