## 4 Discussion  
Adhesion to the denntinal walls of the root canal has been and continues to be the subject of many research topics. Studies on micro infiltration, using different methods of determination, have led to contradictory results, some unfavorable, others favorable. In addition to the issue of micro infiltration, the ability of the tooth to adapt to physiological conditions through a dynamic status of the sealer-dentin interface must be taken into account [25, 26]. SEM and AFM images obtained in the present study showed a more profound penetration into the denntinal tubules for the bioceramic based sealers (both commercial (TotalFill BC and E2-BC). Meanwhile, hydroxyapatite-based sealers have a thinner layer on the interface with the dental structures. The formation of a homogeneous hybrid layer was present in case of all materials, ensuring the closure of any communication path between the root canal and the outside, thus achieving a sealing of the denntinal wound. The E1-DCR material has a composition that allows it to infiltrate the demineralized denntinal structure and succeeds in forming this layer. The failure of its formation means allowing the communication between the endodontic space and the periodontal or oral environment, with the appearance of marginal infiltration [27]. Thus, a communication pathway is created for bacteria, which will colonize the endodontic space in this way. At the same time, water is allowed to enter, which will lead to the hydrolytic degradation of the cement and the connections formed between it and the dental tissues [28]. [PERSON] and collaborators carried out a study comparing the dentin-sealant interface for two commercial sealants: RealSeal and AH Plus at two magnification orders (\(\times 150\) and \(\times 1000\)) using a scanning electron microscope (SEM). They concluded that there are fewer gaps in the dentin/RealSeal interface than in the dentin/AH Plus interface [27]. The formation of the hybrid layer in case of E2-BC sealer is favored by the existence of hydrophilic monomers and of the solvent that the sealer contains. It is well known that it is impossible to completely remove extrinsic wastewater from root canal spaces. As the components of the bioceramic material enable the formation of calcium hydroxide and hydroxyapatite, they ensure an excellent bond to both the dentin and the filling material. Meanwhile they allow the practitioner to perform the microbial control without removing dentin unnecessarily and leaving a stronger root for restorative reconstruction [22]. A problem with hardening of premixed bioceramic sealers could be the lack of moisture in the root canal system, especially in already endodontically treated teeth [26]. Total Fill BC (FKG, Germany) is a bioceramic sealer recognized for its biological properties such as biocompatibility, bioactivity and antibacterial activity as well as for its excellent physic-chemical properties. Unlike conventional filling cements, the setting reaction of Total Fill BC (FKG, Germany) is triggered by the moisture present in the denntinal tubules. Using this moisture, Total Fill BC sealer forms hydroxyapatite, to ensure optimum chemical adhesion between the dentin and the cement [29]. The bond strength of root canal sealers to dentin is important for maintaining the integrity of the seal in root canal filling in both static and dynamic situations. In a static  
Figure 5: Initial situation (**A1**–**D1**), Gutta-percha/sealer interface failure- E2-BC (**A2**), Dentin/sealer interface failure E1-DCR (**B2**), Core material failure—gutta-percha (**C2**)-Real Seal, (**D2**)-Total Fill BC). situation, it should eliminate any space that allowed the percolation of fluids between the filling and the wall; in a dynamic situation, it was needed to resist dislodgement of the filling during subsequent manipulation [13]. In this study, the push-out test method was used to test the dentin bond strengths of different root canal sealers; the model had been shown to be effective and reproducible.