## 4 Discussion  
In the present study, the performance of three reciprocating single-file systems was investigated ex vivo based on their obturuation quality with a matching single-cone gutt-percha point. The stated hypothesis, that the obturuation performance of the three different systems differs significantly, resulting in variations in the percentage of gutta-percha, sealer, and unfilled areas across different sections and configurations of the root canals, had to be rejected. The results of the present investigation revealed no significant impact of the used system, the standardized root canal curvature, or the examined root canal section. Therefore, the null hypothesis, that all three systems showed no significant differences in the composition, could be confirmed. This means that single-cone obturuation using matching  
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gutta-percha points after root canal preparation with reciprocating single-file systems might help to achieve favorable results when focusing on the obturation composition. The treatment steps for sample preparation, application of all materials, and the subsequent evaluation of the slices under the microscope were performed by one researcher, avoiding any influence by other persons. The endodontic treatment of the specimens followed a clinical recommended protocol including all clinical steps. Prior studies suggest that root canal preparation followed by a matching-taper single-cone filling technique offers better shaping and root canal filling quality in the apical third compared to different cold and warm obturation methods, although results are less optimal in the central and cervical portions of the root canals [15; 23]. The result of this study shows that the proportion of gutta-percha is highest in the coronal region at 85% and decreases apically (79%), while the proportion of sealer increases from coronal (14%) to apical (21%) regions. This study shows that the middle area of the canal has the highest proportion of unfilled areas with 1.5%, which can be caused by irregular shapes of the canals or due to the sawing process under water cooling [24]. Additionally, these unfilled areas might be mainly created due the presence of debris after the instrumentation and irrigation of the root canal. The curved canals also have a larger proportion of cavities than the straight canals, although the difference is not significant. In this context, previous studies have shown that the AH-Plus exhibited higher leakage values than other gutta-percha containingand bioceramic sealers [25; 26]. To improve the filling quality of the matching-taper single-cone technique in irregular canals, additional use of vertical and lateral condensation was recommended [15]. In our opinion, a combination of a shape-matched single-cone and isonormal gutta-percha points can also be an option for filling irregularly shaped canals. The bond strength of root canal fillings technique also appears to depend on the sealer [27]. The effect of irrigants on sealer bond strength was also investigated in prior studies. The epoxy resin-based AH-Plus sealer showed no impact in this context, whereas a methacrylate resin-based (RealSeal SE, SybronEndo, Orange, CA, United States) exhibited limitations [28]. Future studies may explore the influence of bioceramic sealers in this regard. Although numerous studies regarding the composition of root canal fillings are available [29; 30], the influence of obturation on clinical success is still discussed controversially and difficult to determine [17; 31]. However, in terms of healing rates of periapical lesions, studies on single-cone obturation methods, using reciprocating file-matched single cones compared to other techniques for obturation, showed equivalent results regarding apical periodontitis healing after treatment [16; 18]. So, regarding the clinical outcome, single-cone obturation might be comparable and seems to have no disadvantages compared to other techniques [17].