## 3 Results
### Evaluation of Animal Experiment  
Four dogs were treated in the frame of the animal experiment as it was carried out. One animal died during root canal treatment, and consequently, the teeth treated in this animal were excluded from analysis. As a consequence, the sample size was n = 5 teeth for groups \"conventional open\" and \"BDD sealed\", while n = 4 teeth were available in groups \"conventional sealed\" and \"untouched\". For the evaluation of periapical radiolucency, the width of the roots in the apical third, as well as the vertical and horizontal dimensions of the defects, were determined (Figures 2 and 3) and statistically analyzed. The mean values and the standard deviations for periapical radiolucency as determined radiographically and histologically are given in Figures 5 and 6.  
Figure 4: Results of cell viability assay for the treatments detailed in Table 1. The mean of confluent and PBS-treated cells was set at 100% value. Panel (**a**) shows the cell viability of HeLa cells after a potentiostatic treatment with a 3 \(\times\) 4 mm electrode immersed in PBS overlaying the cells (direct treatment) for 2.5 min. Panel (**b**) contains the outcome of cell treatment with different commercial irrigants frequently used in dental treatment and their ten-fold dilutions in PBS for five minutes. Panel (**c**) compares direct and indirect treatment of cells and the effect of a treatment with physiological NaCl as a potential electrolyte in comparison to PBS. Note the different scale used for cell viability in panels (**a–c**).  
Figure 5: Mean values of radiographic measurements given in pixels and standard deviations for measurements of periapical radiolucencies in the vertical (dark grey) and horizontal (light grey) directions relative to the width of the respective root.  
The results of the Kruskal-Wallis tests, as well as the pairwise comparisons between the different treatment groups, are given in Tables 3 and 4 for both vertical and horizontal dimensions of periapical defects as determined radiographically and histologically. Comparing radiographic radiolucucency both in the vertical and horizontal directions did not lead to a statistically significant difference among the treatment groups. Based on histologic evaluation, the teeth treated with BDD electrodes showed significantly greater radiolucency as compared to untouched teeth (horizontal direction \(p\) = 0.039 and vertical direction \(p\) = 0.030). No difference could be seen between the conventionally treated and sealed teeth and teeth treated with BDD electrodes (horizontal direction \(p\) = 0.862 and vertical direction \(p\) = 0.940).  
\begin{table}
\begin{tabular}{l l l l l} \hline
**Vertical radiolucency** & & & Kruskal–Wallis test: \(p\) = 0.0427 & \\ \hline  & Conventional open & Conventional sealed & BDD sealed & Untouched \\ \hline Conventional open & & 0.922 & 0.963 & 0.281 \\ \hline Conventional sealed & 0.704 & & 0.998 & 0.096 \\ \hline BDD sealed & 0.208 & 0.878 & & 0.110 \\ \hline Untouched & 0.958 & 0.433 & 0.086 & \\ \hline \multicolumn{4}{l}{**Horizontal radiolucency**} & & Kruskal–Wallis test: \(p\) = 0.0412 \\ \hline \end{tabular}
\end{table}
Table 3: Comparative statistical analysis for vertical and horizontal radiolucency as determined radiographically. Statistically significant differences \(p\) < 0.05 are written in bold.  
Figure 6: Mean values of histologic measurements given in \(\upmu\)m and standard deviations for measurements of periapical radiolucencies in the vertical (dark grey) and horizontal (light grey) directions relative to the width of the respective root.