Mechanical reduction of the intracanal Enterococcus faecalis population by Hyflex CM, K3XF, ProTaper Next, and two manual instrument systems: an in vitro comparative study.

Aim: In the present study, the effectiveness of three rotary and two manual nickel titanium instrument systems on mechanical reduction of the intracanal Enterococcus faecalis population was evaluated.

Methods: Mandibular premolars with straight roots were selected. Teeth were decoronated and instrumented until 20 K file and irrigated with physiological saline. After sterilization by ethylene oxide gas, root canals were inoculated with Enterococcus faecalis. The specimens were randomly divided into five groups for canal instrumentation: Manual Nitiflex and Hero Shaper nickel titanium files, and rotary Hyflex CM, ProTaper Next, and K3XF nickel titanium files. Intracanal bacterial sampling was done before and after instrumentation. After serial dilution, samples were plated onto the Mitis Salivarius agar. The c.f.u. grown were counted, and log10 transformation was calculated.

Results: All instrumentation systems significantly reduced the intracanal bacterial population after root canal preparation. ProTaper Next was found to be significantly more effective than Hyflex CM and manual Nitiflex and Hero Shaper. However, ProTaper Next showed no significant difference with K3XF.

Conclusion: Canal instrumentation by all the file systems significantly reduced the intracanal Enterococcus faecalis counts. ProTaper Next was found to be most effective in reducing the number of bacteria than other rotary or hand instruments.