## 4 Discussion  
One of the most common causes of endodontic therapy failures is bacterial leakage and ineffective eradication of microorganisms from the root canal system. Many variables could affect the leakage, such as the obturation techniques, the properties of the sealer, and the presence of a smear layer [24]. However, complete bacterial removal is not always feasible. Complete sealing is necessary to avoid the entrance of microorganisms from the oral cavity into the root canal system. During obturation, sealers are used to fill the spaces between the core material and the dentin wall. Moreover, they fill lateral canals and/or any canal irregularities [25]. Bio-ceramic sealers have potential importance in clinical practice due to their sealing ability, biocompatibility, hydrophilic nature, antibacterial property, bio-activity, and easy delivery which enhance their promising characteristics in the endodontic field. The bacterial leakage model method was used in this study to evaluate and compare the sealability of two bio-ceramic sealers: MTA Fillapex and CeraSeal, using the single-cone technique and comparing them with the conventional resin sealer AH Plus while using the lateral condensation technique as a benchmark. The results showed that there were several differences in the percentage of samples with no leakage. Within the limitations of this technique [26], our study reported that the CeraSeal group had the highest number of  
Figure 3: Scanning electron microscope micrographs after 60 days showing the sealer/dentin interface at magnifications of \(\times\)500, \(\times\)1000, and \(\times\)2000, respectively, for the tested groups. (**A–C**) Different magnifications of the MF group showing MTA Fillapex with the best adaptation at the root canal dentin-sealer interface (blue arrows). (**D–F**) Different magnifications of the CE group showing CeraSeal bio-ceramic sealer with marked interfacial gaps at the root canal dentinal wall/sealer interface (blue arrows). (**G–I**) Different magnifications of the CO group showing AH Plus with good adaptation with minor interfacial gaps at the root canal dentinal wall/sealer interface (blue arrows). leaked samples (80%) followed by the AH Plus group (50%), and the MTA Fillapex group had the least amount of non-leaked samples (30%). However, no significant difference was detected among the tested groups. The better sealing ability of MTA Fillapex sealer may be due to its high flow rate (27 mm) and low film thickness, so it easily penetrated the lateral and accessory canals, regardless of the obturation technique or obturation temperature. Moreover, MTA Fillapex has excellent antibacterial properties due to the high pH (9.5-10.4) for extended antibacterial action and the tendency toward keeping the Ca\({}^{2+}\) release relatively constant for up to 14 days. Moreover, MTA Fillapex has an extremely low solubility (0.1%) that prevents its erosion with time unlike the other sealers [27]. MTA Fillapex can expand and boost its sealing performance over time, especially if 17% EDTA was used as a final irrigant, as it helps the smear layer fuse to the MTA Fillapex sealer mass and adds volume to the sealer that will penetrate the dentinal tubules [28]. In addition, during the setting reaction of MTA Fillapex, it hydrates inorganic oxide components, which creates Ca\({}^{2+}\) hydroxide and Ca\({}^{2+}\) hydrate phases, forming a covalent bond with the amino group, which results in the expansion of the sealer and improves the overall sealing ability [29; 30; 31]. Furthermore, previous studies showed that bio-ceramic sealers do not shrink during the setting process since they do not contain any monomers, providing a good seal between the sealer and the canal walls [32]. These findings worked with [PERSON] et al. [33], who concluded that MTA Fillapex showed fewer leaked samples when compared with AH Plus over a period of 60 days, although there is no significant difference among the groups.