## 3 Results and Discussion
### In Vitro Electrochemical Study Using Electrochemical Impedance Spectroscopy
The widest plateau ranges were observed for the CoCrMo electrode in an artificial saliva environment with the addition of Meridol(r) (6) and Listerine(r) (5) mouthwashes. The narrowest plateau range was characterized by the tested electrode in a solution of artificial saliva with pH = 7.4 (1). The remaining environments had very similar plateau ranges. The Bode plot in the form of \(\log|Z|=\) f(log f) provides information about the corrosion resistance of the tested material in a given environment (Figure 7). The highest corrosion resistance was demonstrated by the sample in the artificial saliva environment at a neutral pH with the addition of NaF (3); the logarithm value of the impedance modulus at the lowest tested frequency f = 1 mHz was 6.06 \(\Omega\) cm\({}^{2}\). A slight decrease in the log value of \(|Z|_{\text{f = 1 mHz}}\) = 6.03 \(\Omega\) cm\({}^{2}\) was observed in the case of the sample tested in the saline environment (7). For artificial saliva with pH = 7.4 following the addition of Meridol(r) mouthwash (6) (log \(|Z|_{\text{f = 1 mHz}}\) = 5.9 \(\Omega\) cm\({}^{2}\)) and Listerine(r) (5) (log \(|Z|_{\text{f = 1 mHz}}\) = 5.94 \(\Omega\) cm\({}^{2}\)), we observed a slight difference in the impedance modulus, which is caused by the different chemical  
Figure 7: Experimental (symbols) and simulated (lines) Bode diagrams in the form of \(\log|Z|=\) f(log f) for the CoCrMo electrode in the applied corrosion environments at a temperature of 37 \({}^{\circ}\)C.  
compositions of the added fluids. One of the basic factors influencing the corrosion resistance of a material is the chemical composition of the corrosive environment. In an acidic artificial saliva solution after modifying the environment with NaF (4), the \(\log\mid\)Z\(\mid\)\({}_{\text{f = 1 mHz}}\) value was 5.32 \(\Omega\) cm\({}^{2}\), and, in a neutral environment with the addition of NaF (3), the \(\log\mid\)Z\(\mid\)\({}_{\text{f = 1 mHz}}\) value was 6.06 \(\Omega\) cm\({}^{2}\). In the environment of neutral artificial saliva (1), the \(\log\mid\)Z\(\mid\)\({}_{\text{f = 1 mHz}}\) value was 4.62 \(\Omega\) cm\({}^{2}\); this is the lowest value obtained in impedance tests, which is associated with the lowest corrosion resistance of the sample in this environment. Figure 7 clearly shows that the corrosion resistance of the CoCrMo electrode is in the range between good and basic protection against electrochemical corrosion. Depending on the modifiers added to the tested environment, an increase in the corrosion resistance of the tested material can be observed. In the case of a NaF-modified artificial saliva solution (3) (4), fluoride ions act to improve the corrosion resistance of the CoCrMo electrode. The drop in pH (acidification) accelerates corrosion due to the increased intensity of hydrogen depolarization. The corrosion rate increases significantly in the presence of aggressive chloride ions (Cl\({}^{-}\)). Additionally, chloride ions inhibit the formation of passive layers and can also penetrate the oxide layer through pores or lattice defects and destroy it, which then leads to the corrosion of deeper parts of the metal. In order to explain the impedance behavior of the CoCrMo electrode in the tested corrosion environments, the model for the electrical equivalent circuit CPE1, presented in Figure 4, was used. The detailed error in determining the parameters was below 28% (Table 4). The \(\phi\) values ranged from 0.720 to 0.881. The R\({}_{\text{ct}}\) parameter was characterized by the highest value of 1.59(16) \(\times\) 10\({}^{6}\)\(\Omega\) cm\({}^{2}\) for the electrode in the environment of artificial saliva with the addition of Listerine(r) mouthwash (5), which has the strongest protective properties (Table 4). The corrosion resistance decreased successively, but it is of the same order of 10\({}^{6}\) in saline (7), and saliva with pH = 7.4 following the addition of Meridol(r) mouthwash (6). The electrode in the artificial saliva solution with pH = 7.4 + 0.1 M NaF (3) decreased by an order of magnitude.