## 5 Discussion
Therefore, NaCl is highly suggested as the main irrigant due to its broad antibacterial range, its special ability to dissolve necrotic tissue debris and the organic components of the smear layer, and its capacity to eliminate deep-rooted pathogens organized in biofilms and dental tubules [42]. Subsequently, pre-treatment with HP affected PDI disinfection capacity [12; 43]. HP is identified by a moderate antibacterial activity, and the PDI process improves its efficiency due to peroxide activation [44]. Up until now, most studies have investigated the combined use of HP and lasers for managing periodontitis [45; 46]. A previous study from our group, which was performed using a 96-well plate, showed that HP significantly reduces biofilm development and metabolic activity of _E. faecalis_[22]. During the SWEEPS procedure, a laser pulse is delivered to enhance the dynamic movement of irradiated liquid. The primary laser pulse is followed by a subsequent pulse after secondary bubbles have occurred at the fiber tip. This leads to accelerated violent collapse and advances the secondary bubbles deeper into the root canals [29]. These bubbles gradually grow to approach the maximum size. With irradiation cessation, the bubble volume would begin to shrink. With consecutive pulse delivery, secondary bubbles are formed. Due to the collapse of bubbles, cavitation shock waves give rise to strong shear stress acting on the root canal wall, aiding debridement and improving the root canal disinfection efficiency [28]. Therefore, the bacterial biofilm attached to the root canal walls can be simply fragmented and removed [3]. The pulse duration of the SWEEPS technique used in this study was 25 \(\upmu\), which results in a pulse peak power as high as 800 W. This technique generates a physical force in the irrigating liquid and enhances its flow. The auto-SWEEPS cycle was designated in this study as the temporal separation between the SWEEPS laser pulse pair with 200 and 650 \(\upmu\)s. In this regard, the auto-SWEEPS cycle has a further benefit in order to reach an optimal pulse separation with respect to the different activating mechanisms at least twice during each SWEEPS cycle [47]. The results of this study indicate that the dual-stage light strategy (660 or 980 nm diode laser + SWEEPS) is significantly more effective in biofilm removal in comparison with the already highly effective 660 or 980 nm diode laser mediated PDI. As can be seen from Figure 3, the MB + 660 nm diode laser + SWEEPS outperforms the MB + 660 nm diode laser or MB + SWEEPS (1.58 vs. 0.73 or 0.77 log\({}_{10}\) CFU/mL reduction, respectively). Additionally, the HP + 980 nm diode laser + SWEEPS was more than \(\sim\) 5 log\({}_{10}\) CFU/mL more effective than HP + 980 nm diode laser or HP + SWEEPS. This is in agreement with another study where the most effective biofilm removal from the root canal was detected when the curcumin-LED was coupled with SWEEPS [32]. Our findings also show that for biofilm removal from the root canal, although the MB or HP-mediated SWEEPS outperforms the MB or HP-mediated PDI, there are no significant differences between these two groups (\(p\) = 0.982). [PERSON], et al. [48] observed improved bacterial clearance of _E. faecalis_ in root canals using auto-SWEEPS when compared to 3% NaCl alone and photon-induced photoacoustic streaming (PIPS). In addition, this efficacy was confirmed by SEM images, which showed that the SWEEPS group resulted in complete biofilm removal from the canals. Notably, shock waves cannot be emitted in narrow root canals simply during LAI [27]. The higher single pulse energy will rapidly increase cavitation bubbles and slow bubble dynamics at higher laser energies. In addition, the laser pulse-shaping optimization by using the SWEEPS technique enhances the effects of photoacoustic flow [27; 49]. Developing more effective root canal cleaning techniques will improve the disinfecting capability of root canals.