## 4 Discussion
However, an oval-shaped canal configuration and a non-uniform removal of remnants in the root canal could lead to differences in both the percentages and quantity of remnants detected by the two radiographical analyses. Small remnants detected by bidimensional X-rays in a vestibular-lingual projection could result in higher percentages when observed through three-dimensional investigations. The differences shown between the X-ray and CBCT imaging can also be attributed to the different resolution of the two types of imaging and to the blooming effect that radiopaque materials (gutta-percha and bioceramic sealers) can cause when subjected to CBCT examination. This phenomenon has been analyzed in the literature by several studies [32; 33; 34; 35]. The data in Table 2 show an increase in the volume of the filled canal of up to 100% compared to the instrumented canal, as confirmed by other in vitro studies [33; 35]. As observed in the axial sections obtained using CBCT, the filled canal appears larger than the instrumented canal. This finding has important clinical relevance, as it highlights the usefulness of partially removing the filling material before performing CBCT examinations, aiming to reduce the blooming effect and allowing for a more accurate evaluation of the root canal anatomy (including poorly filled lateral canals, potential perforations, or broken instruments). Premixed bioceramic sealers are gaining clinical relevance due to their biointeractivity, apatite nucleation ability and ease of use [4]. In recent years, several clinical studies have been published, analyzing the outcomes of treatments involving these sealers [5; 8; 36]. However, there are still no in vivo studies that evaluate their retreatment outcomes. This research gap highlights a significant area for future investigation. Understanding the retreatability of bioceramic sealers is important for developing comprehensive endodontic treatment protocols. The present study contributes to filling this gap by demonstrating (in vitro) the feasibility of retreating bioceramic sealers and achieving complete apical patency [37], suggesting that the use of Neosealer Flo allows for better apical patency during endodontic retreatment compared to other premixed bioceramic sealers. Our data confirm this, as 100% of the samples achieved apical patency during retreatment. The findings led, therefore, to the rejection of the null hypothesis, revealing differences in the treatment outcomes and thereby challenging the initial assumption that there would be no significant difference between the two techniques. This study has some limitations. First, the decision to decoronate the teeth, while beneficial for improving access and visualization during retreatment, does not correspond to the clinical scenario, where additional challenges such as accessing and cleaning the root canal system are present. Second, while CBCT and X-ray imaging were used to assess the remnants, these imaging modalities have some limitations, such as resolution differences and the potential for the blooming effect, which can affect the accuracy of detecting remnants. Although Micro-CT provides a greater resolution and three-dimensional reconstructions of root canal systems, it was not employed in this study because the aim was to replicate clinically applicable methodologies. Finally, the retreatment procedures were performed 1 month after root canal filling, while clinically, this event may occur after a longer time span (10 or more years). The different aging of the obturation materials could potentially lead to different retreatment outcomes [38].