## 4 Discussion  
This study was designed to assess the ability of four irrigation systems to remove Ca(OH)2 from root canals through a quantitative evaluation. CH paste is a widely used intracanal dressing during root canal therapy due to its alkalinity (pH 12.5) to reduce residual bacteria [4], but the presence of residues on dentin walls can prevent sealer penetration into dentinal tubules, thus compromising the endodontic seal and increasing apical leakage [8]. For the previously mentioned reasons, the intracanal dressings should be completely removed before permanent obturation of the root canal [24]. Many studies have been published regarding the removal of CH or other medicaments from the root canal system using other supplementary systems to the conventional irrigation [15; 16; 28; 29; 30]. The aim of this study was to compare Irrisafe, Endovac, and XP-endo Finisher efficacy with the conventional endodontic needle irrigation. One of the major strengths of the present investigation is represented by the quantitative evaluation performed through SEM images. Different methods have been used to measure residual material inside root canals, spanning from direct visualization to micro-CT, from digital microscopy to scanning electron microscopy [9; 13; 31]. In most of the cases, studies conducted by SEM analysis achieved a semi-quantitative evaluation. Other studies performed using the grooves model had several advantages with respect to studies investigating smooth root canals wall, because the scoring of the groove's cleanness is presumably more reproducible than the percentage assessment of the whole canal [30]. In this study, standardized grooves were not performed in the canals because a quantitative method was used that allowed measuring the total amount of CH left without visual evaluations by different examiners. In particular, a rectangular area of images was selected. Brightness and contrast were adapted to accentuate CH remnants. The threshold function was used to select the contrasted spots to obtain a binary black and white image, permitting accurately measuring the area of the white spots inside the area selected [26]. Moreover, one of the significant criticisms of the SEM investigation to evaluate the CH removal is the difficulty of discriminating between Ca(OH)2 residues and the smear layer or dentin debris, since EDX spectroscopy analysis reveals Ca++ in both  
Figure 4: Representative SEM images of areas used for CH residues evaluation for each kind of treatment and root level from the apex. cases [9]. In the present study, this problem was overcome by using a Barium sulfate-doped paste of Ca(OH)\({}_{2}\). Barium sulfate, probably added by the manufacturer for its X-ray opacity properties, permitted the EDX analysis to perfectly distinguish CH remnants from the dentin debris. According to [PERSON] [31], in the present study, it was decided to preserve the tooth crown as an irrigant reservoir during the endodontic procedures, preventing the same irrigants coronal leak during ultrasonic activation. The main finding of this investigation was that Irrisafe, Endovac, and XP-endo finisher showed significantly better performance than the conventional endodontic needle irrigation when the whole canal was considered, regardless of the coronal, middle, and apical level. Among the three techniques, XP-endo Finisher and Irrisafe were able to remove a significantly higher amount of CH than Endovac. Altogether, the results suggest that the null hypothesis has to be rejected. In a recent study, XP-endo Finisher was less efficient than ultrasonic activation in the removal of CH from apical grooves [30]. These results are in contrast with the present findings probably because, in this study, the CH removal procedures were executed at 37 \({}^{\circ}\)C, and at this temperature, XP-endo Finisher inside the root canal changes shape becoming curved due to the transition from the martensitic state to austenitic state [21,30].