## 4 Discussion
Another advantage of this method is that it allowed root canal sealers to be evaluated even when bond strengths are low. At the apical area, the E2-BC sealer had the highest mean bond strength. In descending order TotalFill BC, E1-HA and Real Seal followed. In the median area, the E1-HA sealer had the lowest mean bond strength and TotalFill the highest bond strength. Regarding TotalFill BC and RealSeal, the results are consistent with the results obtained by [PERSON] et al. [21]. In our study the obturation method used was warm vertical condensation technique in apical third and injection of gutta-percha in the coronal two-thirds. The heat generated during the filling technique can influence sealers characteristics. Previous studies on bioceramic endodontic sealers have reported that the chemical composition has not changed after heating [30, 31]. In addition, bioceramic sealer EndoSequence BC Sealer HiFlow (Brasseler USA, Savannah, GA, USA) underwent an improvement in flow, viscosity, and film thickness after heating [32]. The heat generated by the injected gutta-percha in the median area could explain the variations that occurred in the case of the E1-DCR sealer. [PERSON] et al. concluded that the evaporation of the liquid resin component of the sealer by heat generated during obturation technique could result in a highly viscous sealer that had a limited flow capacity into the patent dental tubules and lower bond strength; in addition, the rate of polymerization may be accelerated by heat and increase shrinkage and decrease bond strength [33]. Another explanation for the lower bond strengths at sealer/dentin interface detected in the groups containing a methacrylate resin-based sealer is the effect of cavity configuration factors (C-Factor: the ratio bonded to unbounded surface). Methacrylate resin-based sealers present greater C-factor, causing more polymerization shrinkage and hence more gap formation and micro-leakage [34]. A significant expansion of 0.20% of TotalFill BC Sealer also determines the disappearance of gaps on sealer/root canal interface, which makes the sealer more effective, with higher strength bond [35]. The environmental conditions affect the hydration of the bioceramic-based sealers and consequentially the material interaction with the environment. However, in vitro material assessment may not be representative of the clinical situation because carbon dioxide present in vivo leads to the formation of calcium carbonate rather than the hydroxyapatite reported in in vitro studies [36]. It is well-known that bioactive glasses have excellent biocompatibility. The SiO\({}_{2}\)-CaO glass with a range of 50-90 mol% SiO\({}_{2}\) in the system was bioactive and formed an apatite layer in simulated body fluid. The bioactivity of the sol-gel biogas nanoparticles with high silica contents is related to the broad distribution of the bonding network between the oxygen and silicon atoms [37]. The appearance of new absorption bands in the BAG and HA-containing sealers at \(\sim\)1400 cm\({}^{-1}\) can be assigned to C-O stretching vibration and therefore to the formation of carbonated apatite that mimics the apatite of bone and dental hard tissues. Some studies determined that the apatite layer formation on the surface of composites reinforced with HA fillers in the SBF solution may resulted from the dissolution of HA particles which can lead to the supersaturation of Ca\({}^{2+}\) and PO\({}_{4}\)\({}^{3-}\) and promote the nucleation and growth of HA crystals [38].