Aim. The aim of this in vitro study was to asses the antibacterial effectiveness of a new laser technique (using an Er:YAG laser equiped with newly designed stripped and tapered tips and low energy output and pulse duration) in extracted and infected root canals. Methods.148 single-rooted human teeth extracted for periodontal reasons were prepared with Mtwo nichel – titanium instruments (Sweden&Martina, DueCarrare-Pd,Italy) by “simultaneous technique” up to 25.06. The apical preparation was then completed to a master apical file, Mtwo Apical 2. After preparation all canals flooded with 17% E.D.T.A., 5% sodium hypochlorite (E.D.T.A. 17% and Niclor 5, OGNA Laboratory, Muggiò - Milan, Italy) and sterile bidistilled water than were dried, autoclaved at 134°C for 17 minutes and stored until use. Ten teeth were not infected as negative control group. All the other 138 teeth were contaminated in its root canal by a pure culture of Enterococcus faecalis producer of biofilm (American Type Culture Collection [ATCC] 29212, Oxoid Limited, Basingstoke, Hampshire, United Kingdom) grown in brain heart infusion broth (BHI) with a concentration of 108. After inoculation, all teeth were incubated at 37 °C in a CO2 for 48 hours. After incubation time, Ten teeth were not treated and formed the positive control group, while the remaining 128 teeth were randomly divided into four experimental groups, composed of 32 teeth each treated with different irrigation and laser methods for 20 seconds. Results. After treatment teeth exhibited bacterial growth were: 9 for group A (28,12%), 4 for group B (12,5%), 16 for group C (50%), 4 for group D (12,5%). The CFUs were compared using a Kruskal-Wallis test and Dunn's multiple comparison test. CFU count was significantly less in group A,B and D than in group C (P<0.05). However no statistical significant differences were found for comparisons between groups: A vs B; A vs D and B vs D (P>0.05). Conclusions. In the conditions of our study, all the laser methods resulted strongly effective in decontaminate the infected root canals, without causing unfavorable temperature rises at the settings used. This subablative laser tecnique with a new tip may be considered a valuable tool for root canal treatment.
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