## 4 Discussion
Furthermore, the use of sealer with gutta-percha results in a thinner sealer film compared to a canal obturated with sealer only. This technique usually exhibits cohesive failure within the thin sealer film [29]. It has been reported that the single-cone technique shows greater leakage than the continuous wave technique [43]. This may be attributed to the relatively large sealer volume associated with the single-cone technique, which encourages the development of voids within the sealer layers [44; 45]. However, it has been suggested that the use of matching cones that are calibrated to the canal preparation could minimize the sealer volume [45]. The BC sealer has previously been reported to be gap-free or to have a small gap at the S/D interface [45]. However, previous research has found little adaptation at the AHP/GP interface and good adaptation at the BC/GP interface [45]. One factor that influences the adhesion ability of sealers to dentin is the chemical composition of the sealer and its interaction with radicular dentin [24]. It has been suggested that the high alkalinity of bioceramic sealers is responsible for the denaturation of the collagen fibers of radicular dentin, which can penetrate the dental tubules and improve the adaptation of the sealer to the dentin wall [33; 34]. On the other hand, the good dentin adaptation of AHP may be attributed to the chemical covalent bond between the dental collagen fibers and the amino groups of epoxy resin [46]; however, its polymerization shrinkage may lead to adhesive AHP/GP failure [35; 36]. AHP-Bio seems to possess properties of both AHP and bioceramics; however, it contains a thickening agent that may be responsible for gaps within the sealer layer, possibly resulting in cohesive failure. Bioactivity is the characteristic property of calcium silicate-based sealers, as their bioactive and/or calcium particles react with the phosphorus of simulated body fluid (SBF) to form a mineral structure similar to that of dentin apatite. It is an important property for improving the adaptation and sealing ability of the sealer [8; 9], as it may help prevent the filling material from dislodging from radicular dentin. Serum can be used similarly to SBFbecause it is typically made of protein, growth factors, hormones and minerals, including phosphorus [22; 47]. Additionally, it has been shown to successfully create an apatite layer over bioceramic materials [21; 22]. To create an apatite layer, the specimens used in the current study were soaked in serum for 30 days. Overall, the current bond strength values in all tested sealer groups were improved after immersion in serum compared to the sealers in the dry condition (Figure 2). This finding is supported by previous research showing that the displacement resistance of calcium silicate-based materials increased after immersion in SBF due to bioactivity and apatite layer formation at the S/D interface [30]. It has been suggested that these materials release calcium ions that react with the phosphorus in SBF, triggering the biomineralization process on the interfacial dentin surface. Calcium silicate-based materials provide mineral deposition similar to tooth structure, leading to the formation of tag-like structures that provide interfacial adaptation and reduce bacterial leakage [48]. This previous finding was confirmed in the current study's SEM analysis, which found a marked decrease in gaps in both bioceramic (BC and AHP-Bio) sealers (Figures 4D and 4E, respectively), which improved displacement resistance. However, due to AHP's lack of bioactivity, large voids were detected within the sealer layer and at the AHP/GP interface after immersion in serum (Figure 4F).