Microbiological evaluation of three endodontic disinfection methods in the treatment of root canal failures

In this study traditional EDTA + sodium hypochlorite endodontic irrigation was compared with Nd:YAG laser irradiation either alone or in combination with EDTA + sodium hypochlorite irrigation, in vivo, for the eradication of infecting microorganisms.Forty three human subjects with good general health and with failed root canal treatment were selected. The criteria included root canals filled within 4 mm from the apex, presence of a periapical radiolucency and a minimum obturation history of 4 years.After removal of the filling material, root canal enlargement (#50), disinfection and medication, root canal samples were taken with sterile paper points (Samples S1, S2, S3 and S4, respectively). Colonies were counted and isolated colonies were identified using traditional microbiological and biochemical and enzymatic methods.Corynebacterium spp; 55,8, Bacillus spp; 39,5, Enterococcus faecalis; 25,5, Streptococcus mutans 25,5 and unidentified oral Streptococcus spp 25,5 % were amongst the most frequently recovered microorganisms in the retreated cases.All disinfection methods significantly reduced the number of cultivable microorganisms (t-test; p<0.05). Sodium hypochlorite + EDTA (Group 1) and laser combined with sodium hypochlorite + EDTA irrigation (Group 3) among the three groups yielded decreased colony counts, however difference were not statically significant (Kruskal-Wallis; p>0,05). Laser treatment, probably due to its physical effect on the root canal dentinal wall, reduced the antibacterial effectiveness of the calcium hydroxide medication.Best colony counts results were taken in group 1 where calcium hydroxide was applied after irrigation with sodium hypochlorite, however differences between the groups were not statistically significant (Kruskal-Wallis; p>0,05).