## 4 Discussion
In contrast to SAI, traditional passive ultrasonic irrigation (PUI) systems use rigid tips or endodontic files, which can cause dentine preparation during activation and may cause irregularities in the root canal surface [25; 63]. The study deliberately included an innovative sonic-based system instead of PUI, because the efficiency of ultrasonic activation was reportedly limited in constrained root canals due to wall contact [64]. Although PUI is regarded as a gold standard, EDDY was reported to perform similarly in terms of debris removal [21; 54; 65]. Another innovative method to activate the endodontic disinfectant during final irrigation is AutoSWEEPS. Here, a fiberglass tip is positioned in the access cavity to produce vapor bubbles, which advance into the root canal without alteration of the canal anatomy. Their collapse causes cavitation and photoacoustic streaming of the irrigant [66; 67]. It is described that dual-pulse laser modalities, like AutoSWEEPS, combined with a flat fiberglass tip, as used in this study, show significantly more debris removal compared to single-pulse laser modalities in an _ex-vivo_-setting [68]. Another clinical advantage over sonic and ultrasonic instruments is the absent risk of instrument fracture [59; 69; 70]. However, the costs for purchase and consumption of laser-based systems are considerable. To our knowledge, no study exists so far that directly compared EDDY and AutoSWEEPS by \(\upmu\)CT-imaging for their ability to remove dentine debris from a complex root canal system. Overall, the results of this study confirmed that CNI is inferior to SAI and LAI regarding hard tissue debris removal. After conventional needle irrigation, approximately 15% of the debris remained in the endodontic system, with up to 50% in the apical third, which is in line with previous studies [11; 21; 54]. In contrast to CNI, SAI with EDDY led to extensive removal of hard tissue debris in the coronal, middle and apical thirds of the root canals. Summarizing data from the three segments, a slight advantage over LAI was observed; however, there was no significant difference between sonic and laser activation in the individual root thirds. LAI also enabled sufficient removal of accumulated artificial debris with a significant advantage over conventional needle irrigation. Remarkably, a few samples showed residual debris in the apical third of the root canals after LAI, which was not observed in any of the specimens after SAI. This finding may be related to the fact that compacted and solid debris in the apical region may be more difficult to remove, since there is no direct mechanical force with LAI. However, literature reports are controversial on this issue: [PERSON] et al. reported a superiority of laser-based PIPS over sonic-activated irrigation (EndoActivator) regarding the removal of artificial debris from artificial grooves in the apical third of root canals [71]. When compared to EDDY, PIPS delivered equal results for hard tissue debris removal [54]. As a further development of the laser-based systems, SWEEPS showed even better results in hard tissue debris removal compared to PIPS [32]. Furthermore, SWEEPS seemed to be advantageous over sonic activation with EndoActivator in terms of smear layer removal [72].