## 2 Materials and Methods  
This study conformed to the Declaration of Helsinki in all respects. The protocol was approved by the Regional and Institutional Committee of Science and Research Ethics, University of Szeged, Hungary (Approval No. : RKEB 52/2018-SZTE). This study was carried out on extracted single-rooted human incisors and canines. The initial sample consisted of 200 specimens extracted at the Faculty of Dentistry, University of Szeged. Only teeth with a single, structurally intact root were eligible for inclusion. Exclusion criteria encompassed previous apical resection, root resorption, double roots, and the presence of metallic restorations. The inclusion and exclusion criteria were assessed through visual inspection. The remaining specimens underwent a progressive selection process as follows: The teeth were first visually examined by transillumination (DiaLux 2300L Kavo, Germany) under 12.5\(\times\) magnification (Zeiss OPMI Pico, Carl Zeiss AG Germany). All specimens with no visible accessory canals (as judged by the presence or absence of foramens) or with visible accessory canals outside the apical third were excluded. The four-eye principle was adhered to during the inclusion and exclusion process of the teeth, as well as in the initial visual selection step. This meant that any single tooth had to be agreed upon by two investigators, ensuring alignment with the specified criteria. The remaining teeth were radiologically tested with a multiscale X-ray microtomograph ([PERSON], Skyscan 2211, Bruker, Belgium). First, a prescan was performed in search of radiologically identifiable lateral canals. Teeth with no detectable ramifications or lateral canals were excluded. Specimens that passed this scan underwent a full scan at 2.5 \(\upmu\)m pixel resolution, using a 1 mm Al filter, with the following source parameters: 110 kV tube voltage, 300 \(\upmu\)A tube current, and 600 ms exposition time. The final study sample consisted of teeth in which lateral canals and/or ramifications could be identified with this method at the apical 3 mm portion of the apex (n = 33) (Figure 2). Figure 2: Flow diagram of screening and selection process of included teeth. The 'Apicoectomy' itself was performed as previously described by [PERSON] et al. [32], with hollow trephine burs of a 4.21 mm outer diameter (Hager & Meisinger, Neuss, Germany) at 800 rpm with a surgical motor (Implantmed W&H Dentalwerk, Burmoos, Austria). Copious water cooling (0.9% saline, 105 mL/min) was applied. The axis of the section was perpendicular to the axis of the root. The apical 3 mm was removed according to the following steps: (1) a line, measured at 3 mm from the tip of the apex, was marked on the root surface with a 0.4 mm point black permanent marker (Stabilo OHPen S, Stabilo, Germany); (2) with the help of Krampon pliers, the tooth was stabilized over a metal sheet with its palatal surface positioned coronally from the marked 3 mm line, to prevent any interference during the sectioning; (3) the trephine bur was held with its uppermost point of outer curvature touching the pre-marked line and perpendicular to the axis of the root (Figure 3). The apicoectomy was followed by micro-CT scanning, with the previously mentioned settings, to detect possible remaining lateral accessory canals and ramifications (SuperNumeraryCanal, SNC, Figure 4). In this study, SNCs were defined as any CT-identifiable additional canal (lateral canal or ramification) beside the main root canal. The number of teeth containing SNCs and the number of SNCs (by counting them in the CT images) were both documented. The complete removal of SNCs with semicircular section was determined in percentage, just like the number of straight cuts necessary to remove the SNCs remaining after the original sectioning method. Calculations were performed for the exact number of SNCs for the latter. The number of SNCs was listed by tooth type (central incisor, lateral incisor, or canine). Calculations were performed on the mean number of SNCs by tooth type as well.