Intracanal microbial reduction after root canal preparation with different tapered instruments. An ex-vivo study.

Aim: The objective of this ex vivo study was to assess the dual impact of instruments taper and irrigation activation methods on bacterial reduction in infected root canals.Materials and methods:42 extracted human molar teeth were inoculated with Enterococcus faecalis for 2 weeks to develop a mature biofilm. The samples were divided into four experimental groups and two control groups. The experimental groups underwent root canal preparation using two different instruments: XP Shaper (taper 0.04) and Reciproc Blue R25 (taper 0.08). Additionally, two different activation methods were tested: mechanical (XP Finisher) and sonic (EDDY). Bacterial reduction was assessed using Colony Forming Unit (CFU) analysis and Confocal Laser Scanning Microscopy (CLSM) to evaluate the efficacy of the treatments.Results: Results showed significant microbial reduction in all groups after root canal preparation. Root canal preparation with the Reciproc Blue R25 (0.08 taper) achieved a significantly higher bacterial reduction compared to the XP-Endo Shaper (0.04 taper). Additionally, EDDY-activated irrigation resulted in a greater bacterial reduction than the XP Finisher. The interaction between instrument taper and activation method was statistically significant (p<0.001), indicating that both factors contribute to the efficacy of microbial reduction in root canals.Conclusion: Both the instrument taper and the method of irrigant activation significantly affected the reduction of intracanal bacterial load. The use of larger tapers and sonic activation provides microbial reductions that may improve clinical outcomes in endodontic treatments.