## 4 Discussion  
The series of experiments described in this study aimed to evaluate the risk of host tissue damage during the application of BDD electrodes during root canal treatment. With the working principle of electrochemical disinfection producing unspecific OH radicals, an optimization between bacterial inactivation and cell viability must be achieved for clinical application. The effect of rinsing solutions such as H\({}_{2}\)O\({}_{2}\), NaCl, and CHX [21] frequently used in endodontics as well as non-surgical and surgical treatment of peri-implantitis has been studied as a control for cell viability. Regardless of the application mode of the BDD electrodes, cell viability was greater in almost all settings as compared to the use of the rinsing solutions. A possible explanation for this phenomenon may be that the only locally formed radicals during the electrolysis of saline are strictly transient. Considering proper disinfection of contaminated root canals a prerequisite for peri-apical healing [2; 5] and acknowledging that none of the existing irrigation solutions and protocols can proof superiority [22] electrochemical disinfection using BDD electrodes was envisaged. In a related paper reporting on the same animals, it has been shown that electrochemical disinfection clearly further reduces the bacterial load as compared to conventional endodontic treatment [15]. Despite being aware of the potential differences in oral microbiota being present in humans vs. animals, the bacteria populating infected root canals were not identified as part of this study [23]. With eliminating bacteria being only one aspect of the treatment, this investigation was aimed at roughly evaluating the host response. As a simple indicator, periapical radiolucency was chosen as a parameter comparable to the clinically applicable radiographic periapical index [24; 25]. In contrast to the other studies, it was neither possible to determine changes of periapical lesions following the endodontic treatment [1] nor to quantify inflammation [26; 27]. Only two out of twelve pairwise comparisons involving teeth treated with BDD electrodes showed significant differences with respect to apical radiolucency. There was no instance where teeth treated conventionally and sealed vs. teeth treated conventionally plus using BDD electrodes and sealed showed a significant difference, indicating that no additional damage had been introduced by electrochemical disinfection. From a clinical perspective, defining successful treatment by the absence of apical periodontitis and clinical symptoms [2], neither of the treatment rendered was successful. In this context, it may also be argued that mechanical instrumentation, only until reaching working length instead of creating apical patency, had led to favorable results. The fact that dog teeth in general do not contain a main apical foramen to connect with the periapical tissues but only an apical delta may be seen as a confounder here. Based on a report indicating that maintaining apical patency did not affect endodontic treatment outcomes in teeth with necrotic pulp and apical periodontitis, it was decided not to overinstrument [28]. As the teeth treated as part of this experiment developed periapical lesions, indicating that no complete healing \begin{table}
\begin{tabular}{l l l l l} \hline
**Vertical radiolucency** & & Kruskal–Wallis test: \(p=\)0.0152 & & \\ \hline  & Conventional open & Conventional sealed & BDD sealed & Untouched \\ \hline Conventional open & & 0.680 & 0.280 & 0.730 \\ \hline Conventional sealed & 0.664 & & 0.940 & 0.170 \\ \hline BDD sealed & 0.167 & 0.862 & & **0.030** \\ \hline Untouched & 0.899 & 0.297 & **0.039** & \\ \hline \multicolumn{4}{l}{**Horizontal radiolucency**} & Kruskal–Wallis test: \(p=\) 0.0178 & \\ \hline \end{tabular}
\end{table} 
Table 4: Comparative statistical analysis for vertical and horizontal radiolucency as determined histologically. Statistically significant differences \(p<\) 0.05 are written in bold.