This study was designed to evaluate the effectiveness of the EndoVac system versus Ultrasonic irrigation in terms of weight of apically extruded debris and cleanliness of smear layer from root canal in vitro after endodontic instrumentation.Sixty extracted human mandibular incisors were selected. The crowns of all teeth were decoronated to allow access to root canal and establish an average root length of 17mm. The root samples were divided randomly into two main groups with thirty teeth per group. Group I experimental (Revo-S) is subdivided into three subgroups of ten each. Subgroup I.a (Macro-cannula) Subgroup I.b(Micro-cannula) Subgroup I.c(Ultrasonic). Group II control (Step-back) is subdivided into three subgroups II.a (Macro-cannula) Subgroup II.b (Micro-cannula) Subgroup II.c (Ultrasonic).The method of evaluation was done by collecting the extruded debris which was evaluated by weight then the specimens were examined under SEM with magnification 1500X to evaluate the cleanliness of smear layer in root canals.The results of the present study revealed the following: a.Weight of debris:In comparison between the two groups, there was no statistically significant difference when using Macro-cannula. However, Control group (Step-back) showed higher mean weight of debris than the experimental group (Revo-S) when using both Micro-cannula and Ultrasonic.In comparison between the irrigation subgroups, with (Revo-S) Ultrasonic subgroup showed statistically highest mean weight of debris, there was no statistically significant difference between Macro-cannula and Micro-cannula techniques; both showed lowest mean weight of debris. While with (Step-back), Ultrasonic subgroup showed statistically highest mean weight of debris followed by Micro-cannula which showed lower mean value while Macro-cannula showed the lowest mean value.b.Smear layer evaluation (Efficiency of canal irrigation)In comparison between the groups at the middle third, there was no significant difference between mean area percent of efficient canal irrigation in the six subgroups.In the apical third there was no statistically significant difference between mean area percent of efficient canal irrigation in macro-cannula subgroups, while there was statistically significant difference between mean area percent of efficient canal irrigation in micro-cannula subgroups and the ultrasonic subgroups.In comparison within Revo-S group in the middle third, the mean area percent of efficient canal irrigation was higher in micro-cannula subgroup followed by macro-cannula subgroup, while the ultrasonic subgroup showed the least mean value. However the difference was not statistically significant.In the apical third, the micro-cannula subgroup showed the highest mean value followed by the macro-cannula subgroup then the ultrasonic subgroup. The difference was statistically significant.In comparison within control group in the middle third, the micro-cannula subgroup showed the highest mean value followed by the macro-cannula subgroup then the ultrasonic subgroup; however the difference was not statistically significant.In the apical third, the mean area percent of efficient canal irrigation was higher in micro-cannula subgroup followed by ultrasonic subgroup, while macro-cannula showed the least mean value; however the difference was not statistically significant between the three subgroups.Conclusions:From the aforementioned results of this study, the following could be concluded:1. The EndoVac system produced less apically extruded debris when compared with the passive ultrasonic irrigation.2. EndoVac system produced fairly clean canals that had lower debris recognizable by scanning electron microscope when compared with passive ultrasonic irrigation.3. Both techniques did not completely remove debris from both the middle and the apical segments.