الفهرس 
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Abstract
T
he aim of the present study was to evaluate the effect of single versus multiple Ni-Ti rotary systems (One shape representing the single file system) and (Protaper NEXT representing the multiple file system) on the bacterial reduction in root canal after the use of different irrigation systems: conventional syringe irrigation with no agitation, conventional syringe irrigation with passive ultrasonic irrigation and apical negative pressure irrigation system (EndoVac).
Seventy human permanent mandibular molars with mature apices were decoronated at length of 16 mm. The root canals were contaminated with Enterococcus faecalis. Samples were divided into three groups according to the instrumentation technique used into:
4. group I: consisted of 30 samples were cleaned & shaped using one shape file.
5. group II: consisted of 30 samples were cleaned & shaped using Protaper NEXT file.
6. group III: Consisted of 10 samples that were not subjected to chemomechanical preparation (n=10). (Negative control group).
Groups I & II were further divided into three subgroups according to the agitation technique used during final flush protocol:
4. Sub group A: consisted of 10 samples that were irrigated using conventional syringe irrigation.
5. Sub group B: consisted of 10 samples that were irrigated using conventional syringe irrigation with passive ultrasonic irrigation.
6. Sub group C: consisted of 10 samples that were irrigated using EndoVac system.
Bacterial colonies were collected & calculated after the procedure & colony forming units were counted.
Results showed that there was no statistically significant difference found between One shape and Protaper Next on bacterial count regardless to irrigation protocol. Also there was no statistically significant difference between passive ultrasonic on one hand and each of conventional syringe and EndoVac on bacterial count regardless to number of files in the NiTi rotary system used. While a statistically significant difference was found between conventional syringe and EndoVac on bacterial count also regardless to number of files in the NiTi rotary system used.