## 4 Discussion  
In this study, we sought to determine in vitro if the efficacy of semicircular apicoectomy performed with a trephine is comparable to that of the conventional straight apicoectomy performed with a bur. We embarked on this exploratory investigation because this method is gaining popularity in practice, yet lacks preclinical evidence to substantiate its non-inferiority compared to the conventional approach to apicoectomy in terms of eliminating SNCs. We hypothesized that the efficacy of semicircular sectioning performed with a trephine would be comparable to that of the conventional straight section performed with a bur. According to our results, the hypothesis was confirmed. In our study, the proposed semicircular method eliminated all SNCs in 94% of the study specimens. Also, when looking at the total number of SNCs, it eliminated 97.3% of SNCs in all study specimens. The given percentages correspond almost exactly to those in the literature regarding the conventional straight-cut approach [11]. The comparison of the two methods did not show any significant difference regarding the complete removal of the SNCs from the apical 3 mm (\(\chi^{2}=1.00\), df = 1, and \(p=0.317\)). The treatment of the 2 teeth (6.1%) out of the 33 specimens with residual canals failed due to reasons that were not related to the method itself. In one sample, the problematic SNC was located coronally to the section line, so that it would have been impossible to remove it by following the conventional straight-line protocol. The presence of the other SNC was caused by operator error: asymmetric sectioning was performed as a result of misaligning the trephine bur to the midline of the root axis (Figure 6). As a result, only one side of the apex was eliminated properly, while a thick, triangular tooth structure remained on the contralateral side, involving the residual SNC. With the precise positioning of the trephine bur, these types of errors can be avoided, and the efficacy of the semicircular technique can be even more similar to the straight-line cut. In live surgeries, with the help of accurate digital planning followed by guided apicoectomy with the help of a 3D-printed surgical template, this operator error can easily be prevented. On the other hand, a misaligned apicoectomy can be intentional in certain cases, as [PERSON] and colleagues pointed out, to preserve adjacent anatomical structures [33]. \begin{table}
\begin{tabular}{l c c c c} \hline  & **Number of Teeth with** & **Number of SNC** & **Number of Teeth without SNC** & **Eliminated SNC** \\ \hline Teeth included in the & & & & \\ last phase & 33 & 72 & NA & NA \\ \hline Microtomograph & & & & \\ results after & 2 & 2 & 31 & 70 \\ semi-curcurcur cut & & & & \\ \hline Microtomograph & & 1 & 32 & 71 \\ results after straight cut & & & & \\ \hline \end{tabular}
\end{table} 
Table 3: Initial SNC numbers and their change after the semicircular and the straight-line apicoectomy (\(\chi^{2}=1.00\), df = 1, and \(p=0.317\), according to the McNemar test). As in most of the in vitro studies, the given optimal circumstances and precise following of the guideline can provide the result of an optimal procedure, resecting the apex exactly at 3 mm from the apex of the root [34; 35; 36]. This presupposes considerable accuracy. An in vivo apicoectomy with a trephine bur, in most of the cases, is a guided procedure, where a static surgical guide is providing stable circumstances. In the field of guided implant dentistry, guided surgery is considered to yield excellent accuracy [37], so that, theoretically, the 3D-printed guide based on the surgical plan and patients' individual anatomy should provide good enough accuracy to achieve the detected high SNC elimination percentages. As this type of guided technique is relatively new in surgical endodontics, hardly any empirical evidence is known to draw firm conclusions from.