## 4 Discussion  
This pilot study analysed the outcome of root canal treatments filled with a recently introduced premixed CaSi-containing biocearamic sealer and warm carrier-based technique. The cumulative percentage of healed teeth was approx. 81.6%, with no extractions. The cumulative survival rate was 100%. These data are in line with previously published studies on carrier-based techniques used with an epoxy resin sealer [2; 3; 4]. A total of 8 teeth still presented a radiographically detectable periapical radiolucency at 12 months, which was stable or improved compared to the preoperative periapical lesion. Approximately half of the endodontically treated teeth had a diagnosis of necrotic pulp (21%) or a re-exacerbated periapical lesion (26%) at baseline. This condition critically affected the 12-month healing outcome, as demonstrated by the statistical analysis in Table 3a,b. Other obturation-related parameters were analysed to assess the potential effect of the sealer and technique on the healing rate of the root canal performed. Interestingly, a high percentage of periapical sealer extrusion (47% of the total) was observed. The analysis of periapical X-rays demonstrated some modification of their morphology or partially complete disappearance over time. The extrusion, at least in the present study, is mainly composed only of sealers. Recent studies confirmed that warm-carrier-based systems may induce a great percentage of extrusion, ranging from approx. 25% to 58% of the cases [23; 29]. A conventional gold-standard sealer (AH Plus), mainly composed of epoxy-resin components, offered a high percentage of radiographic extrusion (30%) [23], likely attributable to the higher flow when heating is applied [34]. In the present study, teeth that showed partial or complete resorption (and radiographic disappearance) of apical extrusion were associated with lower percentages of healing at 12 months but were not statistically significant (\(p>0.05\)). Longer follow-up (4 years, according to the European Society of Endodontology) may reveal a more significant association with the effect of sealer resorption on healing outcome [35]. Only a small number of studies evaluated the presence and the role of periapical extrusion on healing and their effect on clinical results [36; 37]. Previous studies found the non-significant effect of sealer extrusions on periapical healing (such as in the case of epoxy resin-based sealers and calcium hydroxide-based sealers) [36; 37] as also indicated by a recent meta-analysis [38]. The sealer composition, the ability to release bioactive ions, and the bioactivity properties could influence the periapical bone healing and formation of new bone tissue detectable by radiographic inspection [39]. The biological consequences of extrusion are probably modest if the sealer is mainly composed of biocompatible components [40] that induce fast bone regeneration during their degradation and release of bioactive ions [21; 23; 39]. The non-complete healing observed in this study may be explained by the fact that biological phases of periapical bone remodelling need time to remove the sealer radiopacifiers and to complete the bone regeneration. Moreover, the potential bioactivity (apatite nucleation ability) of the sealer could induce the formation of hard tissue in the periapical lesion, which may appear less radio opaque than healthy periapical bone. This aspect needs to be elucidated at longer follow-up to assess if the complete resolution of the periapical healing proceeds or remains stable. In previous times, the use of mineral trioxide aggregate (MTA) and other CaSi-based cement were tested as an approach to achieve effective sealing of wide apexes [7] while simultaneously facilitating the development of a durable and biologically active barrier in proximity to the periapical bone and into the internal surface of the canal. The formation of a biocompatible, osteeconductive cement barrier can stabilise the sealing, potentially stimulating the generation of new bone tissue [41; 42].