## 4 Discussion  
Our own previous work [1; 2] on BDD electrodes, as well as the previous work of [PERSON] et al. [31], showed that flexible BDD electrodes may be applied for electrochemical disinfection in dental root canal treatment. During these proof-of-concept and preliminary studies, the disinfective effect of BDD-processed electrolytes on microbial contaminations was proven using different prototypes. This animal study aimed to explore the potential generalized effects of prototype BDD electrodes intended for electrochemical disinfection [1; 2] during endodontic treatment. Therefore, the focus of this study was not solely put on the electrophysiological effects, but also on design-dependent solutions for possible disturbances caused by different prototypes. With the final arrangement of the anode/cathode not yet determined, two different designs were applied. The design of the electrodes did have an effect on ECoG and ECG, with the anode (BDD-coated Nb wire) positioned inside the cathode (cannula) showing least interference. As expected, in this configuration, the  
Figure 4: Electrophysiological effects of intracavitary stimulation by three differently designed BDD electrodes in comparison with electrotome stimulation and short-circuit effects (representative examples). Note that **(a)** the BDD electrodes inside (i) had no visible effects on ECoG and ECG, while **(b)** BDD electrodes located outside (ii) had significantly stronger electrophysiological effects and even led to short-term epilepsy-like discharges in the ECoG (blue arrowheads). **(c)** The application of AC electrotome (iii) stimulation resulted in the greatest effects on ECoG and ECG, with transient overdrive of ECG and ECG amplifiers. **(d)** Electric shortcuts (iv) induced merely minor ECoG changes. (ECG, electrocardiogram; HR, heart rate; ECoG, electrocorticogram; orange-colored double arrows indicate stimulation periods). electric current follows the path of least resistance and not affecting host tissues. With respect to the prototype design presented by [PERSON] et al. [31] and our previously presented designs [1,2] this new generation of prototypes can be determined as suitable for use for electrochemical endodontic disinfection in living organisms. In contrast, it has been proven that, when BDD electrodes are used, design-related unshielded contact with body fluids leads to significant cerebral and cardiac effects (see Table 2, Figure 4b). Therefore, the main goal of the study was achieved by demonstrating that a design of the BDD electrodes for endodontic electrochemical disinfection could be developed that did not demonstrably cause any relevant electrophysiological cardiac or cerebral consequences in the living mammalian organism. Additionally, we also suggest that designs with direct contact between BDD anodes and patient tissue may lead to effects on human patients if DC currents higher than 20 mA are applied (Figure 1). The investigations carried out revealed that it is obviously essential to prevent the spread of direct current to induce electrochemical disinfection as best as possible. Previous studies have already shown that direct currents in the \(\mu\)A range lead to changes in cortical polarization in rat brains with drastic consequences for cerebral excitability [32,33]. Direct current effects on the heart muscle seem rather unlikely because, due to the anatomical conditions, the heart is hardly in the direct area of influence of potential current flows. In addition, the expected current intensities are several orders of magnitude smaller than those that occur in electrical accidents with heart muscle damage. The recorded ECG effects are most likely caused by electromagnetic interferences when switching on and/or off or possibly by motion artifacts. Altogether, the applicability of DC-driven electrochemical disinfection requires a high level of safety in terms of DC shielding. This also applies to an artificial technical failure with a subsequent electric shortcut.