## 4 Discussion
When NaOCl is used alone for irrigation, it provides better access to the resin cement for its interaction with the hydroxyapatite structure of dentin, so that chemical bonding and sealing can be improved [36]. At the same time, NaOCl application increases dentin roughness and improves frictional bonding, which may be one of the reasons for the high bond strength data [40]. In many studies, ultrasonic devices have been selected as an auxiliary technique to remove the smear layer more effectively [41; 42]. NaOCl/EDTA irrigation with ultrasonic activation performed better regarding the removal of the amount of debris and increased bond strength compared to NaOCl/EDTA irrigation without ultrasonic activation [41]. However, some studies have reported that ultrasonic irrigation has a similar effect to the conventional irrigation technique [42; 43]. In addition, [PERSON] et al. [44] also reported that ultrasonic activation did not have a curative effect on root canal disinfection. The discrepancies may be due to the different experimental setups used and the differences in tested areas. [PERSON] et al. [21] applied NaOCl and EDTA solutions without activation and under PUI activation on posts cemented using a self-etch resin cement and found that the PUI group showed higher bond strength but no significant difference was obtained between the groups. In our study, in the Rely X U200 group, (NaOCl + EDTA) PUI irrigation showed a higher bond strength value than NaOCl irrigation and NaOCl + EDTA irrigation, similar to the results of [PERSON] et al. 's [21] study, but this difference was not significant. In our study, total irrigation times were limited to an average of 40 s. In the PUI group, irrigation-activation cycles for each irrigation solution were performed with a standard protocol with 5 s intervals, similar to previous studies [21; 45]. Previously, this protocol has been recommended by researchers to prevent severe peritubular erosion [46] and also to prevent the possible dangerous effects of temperature increase on the dentin surface due to the use of ultrasonics in the root canal [47], which are the reasons why this protocol was preferred in our study. Since there is no study in the literature in which Panavia V5 was used for post cement, the fact that our data are not fully parallel with the studies using different self-etch resin cements and different results may be due to the structural differences of the materials. In a study on a self-etch cement (Panavia F2.0), it was reported that irrigation with a combination of NaOCl and EDTA caused an increase in bond strength at the post and dentin interface [48]. [PERSON] et al. [49] compared the bond strength of two dual-cure resin cements to dentin and found that Panavia V5 showed a higher bond strength value than its previous version Panavia F2.0 at two different curing conditions, but root dentin was not tested in this study. In our study, as in the study of [PERSON] et al. [32] NaOCl + EDTA and (NaOCl + EDTA) PUI irrigation protocols showed higher bond strength values in the groups where self-etch resin cement was applied. In the control group, this difference was not significant. Phosphate ester monomer 10-methacryloyloxydelyl dihydrogen phosphate (MDP) has been added into various bonding and luting products, such as primers, adhesives, and resins [50]. A recent study stated that post space pretreatment with synthetic hydroxyapatite significantly increased the bond strength of fiber posts luted with 10-MDP-based adhesive techniques [51]. [PERSON] et al. reported that the application of Clearfil ceramic primer plus, which contains MDP phosphate monomer, increased the shear bond strength of PANAVIA(tm) V5 in both zirconia and titanium alloys [52]. Similar results were found in our study. Higher bond strength values were reported in Panavia V5 treated groups that were used with MDP-containing ceramic primer than in Rely X U200 treated groups without ceramic primer.