## 4 Discussion
The correct interpretation of the results is probably that trephine TEMS is comparable to pilot drill TEMS in terms of accuracy (the latter being significantly more accurate than the conventional freehand approach, as shown in previous studies [29; 31]). As the accuracy of all surgical procedures is multifactorial, every single parameter can gain overall success. Fortunately, the depth of apicoectomy is less than other guided surgical interventions'; in this way, the difference in DGD can be decreased while maintaining the same importance in practice. Our research group already published accurate data about trephine osteotomy [26]. That study concentrated on the contribution of the depth stop to the accuracy of the procedure. The mean DGD was 0.92 mm when the trephine had a depth stop and 2.35 mm when it did not. Naturally, only the data from the depth stop trephine group can be compared with the data of the present study. One should not overlook the fact, however, that our previous study was carried out in porcine mandibles to provide human-like circumstances during apicoectomy. The mineral content and bone hardness of the porcine mandible are similar to those of human bones, which suggests that the trephine can be more precise in realistic conditions when the penetration depth is under physical control [36; 37; 38; 39]. Another preclinical study was published by [PERSON] et al. in 2021 [40]. The authors performed 40 osteectomies on cadavers. Trephine osteectomies were performed without a control group. The mean DGD was 1.23 \(\pm\) 0.38 mm, which is almost the same as what we found in this study. They further emphasized that there was no noteworthy distinction in the precision of osteectomies performed by experienced surgeons and dental students, thereby demonstrating the applicability of this approach to ensure the safety of apicoectomy across varying levels of expertise. As for AD, this is a parameter that is usually not reported in the literature in connection with TEMS (in contrast to studies on the accuracy dental implantology), while angulation is obviously not irrelevant in this context either. AD can have a severe effect on the precision during the removal of the apical 3 mm, since the presence of lateral canals and ramification in the apical third are the common causes of persisting apical infection [41]. Any deviation in this area can result in the failure to remove the infected tissue, hindering the healing chances and the survival of the tooth. In this respect, our study definitely offers new information. In this study, we found a mean AD of 3.3\({}^{\circ}\) for the pilot drills and 3.5\({}^{\circ}\) for the trephines. As said, due to the lack of data, a direct comparison with other TEMS studies is not possible, but in the literature on guided dental implantology, similar values are associated with the highest achievable accuracy [35; 42; 43; 44; 45]. As the method itself is based on the guided implantation steps, the results found by [PERSON] et al. on freehand-guided pilot and fully guided drilling can help to compare our results. The fully guided procedure was significantly better (2.30\({}^{\circ}\), standard error 0.92\({}^{\circ}\)) regarding AD than the accuracy of the freehand (6.99\({}^{\circ}\), standard error 0.87\({}^{\circ}\)) or guided pilot (5.95\({}^{\circ}\), standard error 0.87\({}^{\circ}\)) group [42]. The main reason why implant guide studies can provide slightly better AD results is probably the difference in the support of the guide. In most surgical studies, the guide is tooth-supported, while in the case of periapical surgery, the guide extends into the vestibular, modifying the support from dental to muco-dental or dento-mucosal. This seemingly small alteration can have a severe effect on the precision of these procedures.