## 1 Introduction  
After the chemical-mechanical preparation of root canals, residues precipitate on the dentin surface, causing obstruction of the dentin tubules and compromising the adhesion interface with endodontic sealers [1, 2]. On the other hand, these residues can dislodge and/or solubilize over time, causing apical marginal infiltration and consequently compromising the success of endodontic treatment due to possible contamination of the root canal [3, 4]. A sodium hypochlorite solution is usually recommended for root canal irrigation, especially associated with 17% EDTA as a final irrigation protocol [5, 6, 7, 8]. However, this clinical strategy shows several biases, such as the risk of dentin erosion and reduction of intertubular dentin [5]. To minimize these negative effects, the use of devices that provide mechanical agitation of the final irrigating solutions has been recommended to avoid direct chemical action on the dentin substrate [9]. The passive ultrasonic irrigation protocol uses inserts that promote acoustic wave propagation in the irrigation solution [10]. When these waves reach the dentin surface, they promote the displacement of the residues due to the local shear force exerted between the irrigation solution and radicular dentin [11; 12]. However, ultrasonic tips have low flexibility and need to oscillate freely in the root canal, which are factors that limit their use [13; 14]. Nickel-titanium instruments for irrigation solution agitation are more flexible than the inserts used in the PUI and increase root canal irrigation with safer strategies, minimizing the risk of insert separation and damage to the root surface, especially in canals with anatomical complexities [15]. The XP-Endo finisher is an #25 Ni-Ti instrument, and when activated by body temperature, its martensitic phase changes straight into an austenitic phase [15]. The instrument was introduced as an adjunct to agitate the irrigating solution, demonstrating similar potential for removing the smear layer from the canal when compared to PUI [16; 17], as well as providing a significant reduction in root canal microorganisms [18; 19]. The XP Clean is also an #25 Ni-Ti instrument, with a triangular cross-section and structural characteristics similar to the XP Endo finisher. To minimize costs, a plastic device (25.04) was recently designed to agitate the irrigation solution in root canals (Easy Clean). There are reports in the literature that this system provides greater debris removal than PUI without damaging the dentin surface due to its flexibility and dynamic use [2; 20]. An adequate interaction between the dentin substrate and the endodontic sealer used for root canal obturation provides a reliable adhesion interface and better treatment prognosis. Therefore, residues derived from the chemical-mechanical preparation can have negative effects on this adhesive interface, allowing root canal recontamination, mainly during long-term follow-up [1; 3]. Recently, many endodontic sealers have been introduced into the endodontic arsenal, among which hydraulic calcium silicate-based sealers have attracted attention due to their biological properties [21]. However, some of the physicochemical properties of these materials are worrying, such as their high solubility [22]. On the other hand, the irrigation protocol strategy can have an immediate positive impact on the bond strength of the calcium silicate-based sealer in root dentin [23]. Despite this, there are no studies that evaluated the interaction between root canal irrigation protocols using mechanically activated devices and endodontic obturation in the long-term. Thus, the objective of this study was to evaluate the residue incidence and the open dentinal tubules after final root canal irrigation using mechanical activation (XPE, XPC, or ECL) in comparison to PUI through SEM analysis.