Efficacy of different sterilization methods on the inactivation of bacterial endotoxin LPS adhered to endodontic files

The purpose of this study was to evaluate the presence of bacterial endotoxin LPS adhered to endodontic files, after in vitro contamination with E. coli LPS and subsequent sterilization in either autoclave or Pasteur oven (dry heat sterilizer), with or without previous immersion in a solution of calcium hydroxide PA and pyrogen-free water (HC). Seventy K-files were randomly assigned to five groups: Group I - contamination with LPS + sterilization in Pasteur oven; Group II - contamination with LPS + sterilization in autoclave; Group III - contamination with LPS + immersion in HC + sterilization in Pasteur oven; Group IV - contamination with LPS + immersion in HC + sterilization in autoclave; Group V - contamination with LPS; Group VI - contamination with LPS + immersion in HC and Group VII - files taken directly from the original package, as supplied by the manufacturer (not subjected to any sterilization method). LPS quantification was done using the kinetic Limulus Amoebocyte Lysate test (kinetic QCL) and the results were analyzed statistically by the t-test. The amount of LPS in the files of groups I to IV, VI and VII was less than 0.005 EU/mL, and no statistically significant difference was observed (p=0.0003). Only in the group V the average value recorded 0.262 EU/mL ± 0.1624. These results lead to the conclusion that both autoclave and Pasteur oven sterilization methods were effective in inactivating LPS adhered to endodontic files, without need of previous immersion in calcium hydroxide solution.

 

Key-words: “Limulus Amebocyte Lysate”, Kinetic-QCL^TM, endotoxin, LPS, calico hidroxin, autoclave, Pasteur oven.