Objective: Recent studies have shown that the apical negative-pressure irrigation system EndoVac (Discus Dental) produces better disinfection and cleanliness at the apical third of root canals than current irrigation methods using positive pressure. The aim of this histologic study was to compare the EndoVac system at two different exposure times to the traditional positive-pressure irrigation technique for root canal cleaning efficacy and to measure the volume of irrigation at the apical third. Method and Materials: Fifty extracted human incisors, canines, and premolars (with one canal) were used. All teeth were stored in sterile saline and then randomly assigned to one of three experimental groups of 15 each. All teeth were cleaned and shaped at working length using Profile Series 29 (Dentsply Tulsa) to a size 6 (ISO size 36) or larger depending on the first instrument to bind at the apical third. After working length was reached with the master apical file, apical irrigation was accomplished with 6% sodium hypochlorite (NaOCl) over a predetermined time for each group as follows: group 1, EndoVac for 210 seconds; group 2, EndoVac for 150 seconds; group 3, traditional positive-pressure irrigation for 210 seconds. The amount of debris left in the canals was quantified at 1 and 3 mm from working length. Results: No statistical differences were found at 3 mm from working length. At 1 mm from working length, an overall test of association was significant when comparing across the three groups (P = .03). Conclusion: The apical negative-pressure irrigation system EndoVac has the potential to achieve significantly better root canal cleaning at the apical third of root canals and in less exposure time than required with traditional positive-pressure irrigation. Keywords: apical negative-pressure irrigation, canal preparation, exposure time, irrigation, volume