Introduction: The aim of this study was to determine the efficiency of 4 irrigation systems in eliminating bacteria in root canals, particularly in dentinal tubules. Methods: Roots of human teeth were prepared to 25/04, autoclaved, and inoculated with Enterococcus faecalis for 3 weeks. Canals were then disinfected by (1) standard needle irrigation, (2) sonically agitating with EndoActivator, (3) XP Endo finisher, or (4) erbium:yttrium aluminum garnet laser (PIPS) (15 roots/group). The bacterial reduction in the canal was determined by MTT assays. For measuring live versus dead bacteria in the dentinal tubules (4 teeth/group), teeth were split open and stained with LIVE/DEAD BackLight. Coronal, middle, and apical thirds of the canal dentin were scanned by using a confocal laser scanning microscope (CLSM) to determine the ratio of dead/total bacteria in the dentinal tubules at various depths. Results: All 4 irrigation protocols significantly eliminated bacteria in the canal, ranging from 89.6% to 98.2% reduction (P < .001). XP Endo had the greatest bacterial reduction compared with other 3 techniques (P < .05). CLSM analysis showed that XP Endo had the highest level of dead bacteria in the Coronal, middle, and apical segments at 50-mu m depth. On the other hand, PIPS had the greatest bacterial killing efficiency at the 150-mu m depth in all 3 root segments. Conclusions: XP Endo appears to be more efficient than other 3 techniques in disinfecting the main canal space and up to 50 Am deep into the dentinal tubules. PIPS appears to be most effective in killing the bacteria deep in the dentinal tubules.