## 4 Discussion
These differences include: (1) the volume of the solution used is very different between the multisonic technology (350 mL) and conventional irrigation (39 mL [57]); (2) the conventional technique uses intermittent irrigation while the multisonic technology uses continuous refreshing of fluids for 6.5 min; and (3) conventional irrigation uses laminar fluid flow in which the multisonic technology uses a combination of vortical flow and broad-spectrum acoustic energy. These differences may explain the multisonic technology's ability to better dissolve pulp tissue as well as remove bacteria. [PERSON] et al. [25] performed a meta-analysis comparing passive ultrasonic irrigation to conventional irrigation techniques. The study demonstrated that there is no statistically significant difference in the presence of bacteria between the two techniques and there is bacteria remaining in the root canal system. Using histological evaluation of cleaning with ultrasonic irrigation, [PERSON] et al. [58] showed that ultrasonic irrigation for 1 min in each canal after hand/rotary instrumentation cleaned the canals well 1-3 mm from the apex but the results for the isthmus region were not consistent over the same range. [PERSON] et al. [59] showed that ultrasonic irrigation and hand irrigation removed more pulp debris from round-shaped canals compared to oval-shaped canals. This study shows that the multisonic technology with minimal instrumentation of 20/04 is sufficient to remove pulp tissue and disinfect the main canal, isthmuses, and lateral canals at all levels regardless of the shape of the canal. This finding is consistent with a previous study using the same technology where non-instrumented premolars were evaluated with scanning electron microscopy and it was demonstrated that predentin and tissue were removed [40]. In addition, [PERSON] et al. [28] histologically evaluated mandibular and maxillary molars that were instrumented to 15/04 and they found the canals free of pulp tissue in 97.2% of mesial roots and 96.52% in the distal root. This study's results are consistent with the [PERSON] study. Root canal anatomy and root curvature are of main importance in the efficacy of ultrasonic irrigation. [PERSON] [60] compared passive ultrasonic irrigation (PUI) and continuous ultrasonic irrigation (CUI) in an artificial model. CUI had better results but had several disadvantages, including extrusion of irrigants beyond the root canal which compromises the safety of the technique and the possibility of creating a ledge if the irrigation needle is positioned beyond the root canal curvature. With the multisonication technology of the GentleWave System, the irrigation solution is able to reach the total length of the root canal with less likelihood of the solution being extruded into the periapical tissues due to negative apical pressure [29; 61]. The degassed solutions used in the GentleWave system could eliminate vapor lock from the apical portion of the root canal system, when compared to sonic and ultrasonic [61]. [PERSON] et al. [62] found that apical negative pressure (ANP) was the only technique able to deliver the irrigation solution to the full working length, while passive ultrasonic irrigation (PUI) was able to reach lateral canals but was unable to break vapor lock. In a histological study in mesial roots of lower molars, [PERSON] et al. [20] compared the efficacy of apical negative pressure (ANP) and manual dynamic irrigation (MDI) in the removal of debris from the isthmus area. The findings were similar in both groups with slightly better removal using ANP, especially in narrower isthmuses. [PERSON] [63] demonstrated better tissue dissolution obtained by GentleWave when compared to the same amount of NaOCl delivered by a size 19G needle attached to a syringe in a 5 min period. The technology uses degassed fluids which improves the implosive effect of the cavitation since the entrained air in non-degassed solutions can cause damping of acoustic and hydrodynamic energy [64].