Mechanical and chemical debridement plays an important role in reducing intracanal microorganisms. Effective root canal irrigation depends on both the root canal irrigant and irrigation system. The objective of this study was to evaluate the debridement efficiency of four root canal irrigation systems, Endovac®, PiezoFlow™, EndoActivator® and traditional needle irrigation using saline as an irrigant. Seventy-five, single canal, extracted, mature teeth were selected. Teeth were standardized to canal lengths of 15 mm and instrumented to Master Apical File size #40 with 4% taper. Teeth were mounted in a centrifuge tube using PVS impression material. Teeth were randomly divided into four experimental groups (n=15) and one control group (n=15). The root canals were inoculated with 24-hour culture of Streptococcus mutans and incubated for 72 hours. Saline was delivered via each of the irrigation systems at the rate of 7 ml/min using a precision syringe pump. Immediately following the treatment, samples were collected from the untreated control and the experimental groups and plated on agar plates. Results were analyzed using repeated measures ANOVA and Tukey’s HSD multiple comparison tests. All the experimental groups were significantly better than the control group (p<0.0001). Among the experimental groups, Endovac® and PiezoFlow™ were significantly better in reducing microorganisms compared to needle and EndoActivator® groups (p<0.05). There was no statistical difference between Endovac® and PiezoFlow™. Debridement efficiency of Endovac® and PiezoFlow™ is better than needle and EndoActivator® irrigation systems using saline as an irrigant. Funded by Alexander Fellowship, VCU School of Dentistry.