Passive ultrasonic irrigation in the presence of a low concentration of hydrogen peroxide enhances hydroxyl radical generation and bactericidal effect against Enterococcus faecalis

Abstract

Chemomechanical procedures can be used to eliminate bacteria from root canals. However, detectable bacteria sometimes remain because of the complexity of the root canal system. Endodontic passive ultrasonic irrigation (PUI) with hydrogen peroxide (H₂O₂) may be a promising option for increasing bactericidal hydroxyl radical (HO^•) generation. In this in vitro experiment, we examined the effects of HO^• generated using PUI and a low concentration of H₂O₂. An ultrasonic tip was submerged in 0.45 mol/L (1.5%) H₂O₂ in a microfuge tube. H₂O₂ was activated by an ultrasonic unit, the tip of which was kept centered in the tube, to mimic PUI. HO^• generation was detected by electron spin resonance spectroscopy. An Enterococcus faecalis suspension in H₂O₂ was then preparedand activated as described above. Bactericidal effects were assessed by viable counting. Two-way analysis of variance and Tukey’s test were used to assess the statistical significance of differences among groups (P < 0.05). HO^• generation and bactericidal activity were significantly increased by PUI in H₂O₂ in a time-dependent manner and were significantly higher than with H₂O₂ alone or with PUI in a Tris-HCl suspension. These results suggest that PUI in the presence of a low H₂O₂ concentration is a promising new disinfection strategy. (J Oral Sci 56, 35-39, 2014)