## 3 Results and Discussion
### Scanning Kelvin Probe Study of the CoCrMo Alloy Surface  
Using the SKP method, the surfaces of the CoCrMo electrode subjected to the corrosion process in various solutions were analyzed. The SKP technique allowed for the determination of the contact potential difference (CPD) distribution on the sample surface (Figure 9). Based on the registered 3D maps, parameters characterizing the surface state, such as the arithmetic average of CPD heights (\(\text{CPD}_{\text{av}}\)), the root mean square deviation of  
Figure 9: Exemplary contact potential difference (CPD) map for the CoCrMo electrode after corrosion tests in: (**a**) (1) saliva with pH = 7.4; (**b**) (6) saliva with pH = 7.4 + 15 mL of Meridol®; (**c**) (3) saliva with pH = 7.4 + 0.1 M NaF; (**d**) (2) saliva with pH = 5.5. CPD heights (CPD\({}_{\text{rms}}\)), the skewness (CPD\({}_{\text{sk}}\)), and the kurtosis (CPD\({}_{\text{ku}}\)), were determined and are shown in Table 5. The highest average contact potential difference value was obtained for the sample tested in saliva with pH = 5.5 (2). Samples after the corrosion tests in saliva with pH = 5.5 + 0.1 M NaF (4) and saliva with pH = 7.4 + 0.1 M NaF (3) exhibited approximately 50% lower values of CPD\({}_{\text{av}}\) compared to samples after being tested in saliva with pH = 5.5 (2). In turn, the CPD\({}_{\text{av}}\) determined for samples after being tested in saliva with pH = 7.4 + 15 mL of Meridol(r) (6) was around 80% lower. For the samples tested in saline with pH = 7.4 (7), saliva with pH = 7.4 + 15 mL of Listerine(r) (5), and saliva with pH = 7.4 (1), the averages of measured CPD heights were 2.1, 2.7, and 3.1 times lower, respectively, compared to the samples after being tested in saliva with pH = 5.5 (2). The CPD\({}_{\text{av}}\) parameter suggests that the samples tested in saliva with pH = 5.5 (2) exhibited the lowest electrochemical activity among all the tested samples. In contrast, the sample subject to corrosion tests in saliva with pH = 7.4 (1) had the most electrochemically active surface. Keeping in mind that the material from which the samples were made was the same and that the samples underwent similar potential current treatments, it can be concluded that measured CPD\({}_{\text{av}}\) values depend on the composition of the solution. Thus, the sample tested in saliva with pH = 5.5 (2) was most likely subjected to the least aggressive environment, whereas the sample studied in saliva with pH = 7.4 (1) was soaked in the most aggressive one. The CPD\({}_{\text{rms}}\) values determined for samples in all corrosion solutions varied from 17 mV to 21 mV. This indicates that the deviation of CPD heights from the average value is comparable for all the investigated samples. Skewness and kurtosis quantitatively describe the shape of the CPD distribution. As shown in Table 4, both parameters vary from about \(-\)0.1 to about 0.2, indicating that the CPD distribution is of a Gaussian type. Moreover, CPD\({}_{\text{sk}}\) and CPD\({}_{\text{ku}}\) close to zero indicate that the contact potential difference heights are symmetrically distributed around the average and that no areas with relatively large/small CPD values are observed on the examined surfaces. CoCrMo alloys have been widely used in dentistry for many years for partial dentures, replacing gold alloys [22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39]. During prosthetic and clinical treatment, one of the most important aspects is the precision of the reconstruction. Clinical studies show that the proper reconstruction of the tooth crown guarantees durability and prevents the infiltration of bacteria into the tissues [34]. Research shows that, in CoCrMo alloys, metal ions constituting the alloy components are released into the body to a small extent, even in an acidic environment [35; 36; 37; 38].