An in vitro comparison of the bactericidal efficacy of lethal photosensitization or sodium hyphochlorite irrigation on Streptococcus intermedius biofilms in root canals

Abstract

Aim: To compare the bacterial killing of Streptococcus intermedius biofilms in root canals using lethal photosensitization with various combinations of photosensitizer concentration and laser light dose or 3% sodium hypochlorite (NaOCl) irrigation.

Methodology: Extracted teeth (n = 35) with single canals were selected and the canals prepared to apical size 25 with a 10% taper. The teeth were autoclaved and the canals inoculated with Streptococcus intermedius in brain heart infusion broth and were incubated for 48 h to allow a biofilm to form. The teeth were then subjected to 3% NaOCl irrigation (n = 4) or lethal photosensitization using combinations of a range of toluidine blue O (TBO) photosensitizer concentrations (12.5, 25, 50, 100 microgram/mL-1) and light doses (60, 90, 120, 300, 600 s equivalent to energy doses of 2.1-21 J) using a 35-mW helium-neon low power laser targeted at the access cavity (n = 4 for each combination). Controls consisted of laser light only (TBO = 0 microgram/mL-1) (n = 4), TBO only (light dose = 0 s) (n = 4), and no treatment (positive control n = 17). Following treatment the canal contents were sampled with sterile paper points, the sample was dispersed in transport medium, serially diluted and cultured on blood agar to determine the number of colony forming units (CFU).

Results: The combination of 100 microgram/mL-1 TBO and 600 s (21 J) of laser energy achieved maximum reduction in recovered viable bacteria (5 log10 CFU). TBO at low concentrations (< or =50 microgram/mL-1) was not bactericidal but treatment with 100 microgram/mL-1 TBO alone reduced recovered viable bacteria by 3 log10 CFU. Laser light alone had limited bactericidal effect. No viable bacteria were recovered following treatment with 3% NaOCl.

Conclusions: The combined use of a photosensitizing agent and a low power laser directed at the access cavity was bactericidal to S. intermedius biofilms in root canals but was unable to achieve total kill, unlike 3% NaOCl.