## 3 Results and Discussion
### In Vitro Electrochemical Study Using Electrochemical Impedance Spectroscopy
Saliva with pH = 5.5 before (2) (R\({}_{\text{ct}}\) = 6.6(11) \(\times\) 10\({}^{4}\)\(\Omega\) cm\({}^{2}\)) and after the addition of NaF (4) (R\({}_{\text{ct}}\) = 2.71(16) \(\times\) 10\({}^{4}\)\(\Omega\) cm\({}^{2}\)), and in saliva with pH = 7.4 (1) (R\({}_{\text{ct}}\) = 3.71(21) \(\times\) 10\({}^{4}\)\(\Omega\) cm\({}^{2}\)), was characterized by the lowest R\({}_{\text{ct}}\) values. The smaller the R\({}_{2}\), the faster kinetics of the pitting corrosion of the CoCrMo electrode. Extrapolating a straight line with a slope equal to \(-1\) in the Bode system \(\log\mid\)Z\(\mid\) = f(logf) allows the parameter that ascertains the capacity of the electrical double layer (C\({}_{\text{dl}}\)) to be determined (Table 4). A high C\({}_{\text{dl}}\) value indicates the greater exposure of the CoCrMo electrode surface to pitting corrosion due to the faster kinetics of the electrochemical process. Based on the discussion of results obtained using the EIS method, it can be concluded that the corrosion resistance of the CoCrMo dental alloy improved, caused by the presence of Meridol(r) (6) and Listerine(r) mouthwashes in a neutral environment. Both the acidic reaction of the environment and the presence of Cl\({}^{-}\) ions reduced the corrosion resistance of the tested electrode in the environment of body fluids. Chloride anions \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Electrolyte Type** & **R\({}_{\text{I}}\)** & **CPE\({}_{\text{I}}\)-T** & \multicolumn{2}{c}{**R\({}_{\text{2}}\)**} & **C\({}_{\text{dl}}\)** \\  & **(\(\Omega\) cm\({}^{2}\))** & **(F cm\({}^{-2}\) s\({}^{\phi-1}\))** & **CPE\({}_{\text{I}}\)-\(\phi\)** & **(\(\Omega\) cm\({}^{2}\))** & **(F cm\({}^{-2}\))** \\ \hline (1) saliva with pH = 7.4 [30] & 11.72(92) & 0.74(9) \(\times\) 10\({}^{-5}\) & 0.880(14) & 3.71(21) \(\times\) 10\({}^{4}\) & 4.11 \(\times\) 10\({}^{-6}\) \\ (2) saliva with pH = 5.5 & 10.33(65) & 0.24(2) \(\times\) 10\({}^{-5}\) & 0.720(6) & 6.6(11) \(\times\) 10\({}^{4}\) & 7.72 \(\times\) 10\({}^{-6}\) \\ (3) saliva with pH = 7.4 + 0.1 M NaF & 12.13(63) & 0.14(12) \(\times\) 10\({}^{-4}\) & 0.862(8) & 4.10(35) \(\times\) 10\({}^{5}\) & 7.00 \(\times\) 10\({}^{-6}\) \\ (4) saliva with pH = 5.5 + 0.1 M NaF & 9.64(61) & 0.37(3) \(\times\) 10\({}^{-5}\) & 0.820(10) & 2.71(16) \(\times\) 10\({}^{4}\) & 7.77 \(\times\) 10\({}^{-7}\) \\ (5) saliva with pH = 7.4 + 15 mL of Listerine® & 7.79(32) & 0.83(4) \(\times\) 10\({}^{-5}\) & 0.843(4) & 1.59(16) \(\times\) 10\({}^{6}\) & 5.26 \(\times\) 10\({}^{-6}\) \\ (6) saliva with pH = 7.4 + 15 mL of Meridol® & 27.43(35) & 0.27(6) \(\times\) 10\({}^{-5}\) & 0.800(16) & 1.03(29) \(\times\) 10\({}^{6}\) & 9.97 \(\times\) 10\({}^{-7}\) \\ (7) saline with pH = 7.4 & 6.39(34) & 0.14(9) \(\times\) 10\({}^{-4}\) & 0.881(5) & 1.43(17) \(\times\) 10\({}^{6}\) & 7.81 \(\times\) 10\({}^{-6}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameters of the electrical equivalent circuit obtained on the basis of the CNLS fitting of experimental EIS data for the CoCrMo electrode in the biological environment at 37 \({}^{\circ}\)C (see Figures 5–7). initiated the growth and expansion of pits in the self-passive oxide layer on the electrode surface, which were the main causes of the deterioration of parameters, such as \(\mathrm{R_{ct}}\), as confirmed by the corrosion current density values determined in direct current electrochemical tests. The \(\mathrm{C_{dl}}\) values for the CoCrMo electrode in a physiological saline (1) were relatively high, which proves the material's strong ability to corrode in an environment containing \(\mathrm{Cl^{-}}\) ions. The addition of NaF to the artificial saliva environment reduced the \(\mathrm{C_{dl}}\) value in both acidic (4) and neutral (3) environments. The increase in \(\mathrm{R_{ct}}\) value was caused by modifications in the corrosive environment in the form of mouthwashes. A change in the pH of the electrolyte may destabilize the passive layer due to local anodic reactions.