Aim: In this in vitro study we investigated the bactericidal effects on root canals of 2940-nm Er:Yag laser irradiation combinated with sterile saline solution, E.D.T.A. or sodium hypochlorite irrigation. Methods and Materials: Eighty-one single-rooted human teeth extracted for periodontal reasons were randomly divided into five experimental groups, composed of 15 teeth each. 8 other teeth were assigned randomly to 2 groups of control. The root canal of 83 teeth was prepared with Mtwo Ni-Ti instruments by simultaneous technique. All teeth were sterilized in an autoclave at 134 °C. 79 of these were contaminated in its root canal by a pure culture of vancomycin-resistant Enterococcus faecalis grown in brain heart infusion broth (BHI) with a concentration of 108 . The four teeth not contaminated constituted the negative control group. The 79 contaminated samples were incubated at 37°C for 7 days in micropipettes Eppendorff filled with agar, adding new broth every 24h. Spent the week of incubation, the 79 contaminated teeth, were divided randomly into 5 groups each consisting of 15 teeth, while the control group is composed of 4 infected teeth. To assess the bacterial effect of laser Er: Yag 2940 nm have constantly used always the same parameters. An endodontic conical laser fiber tip, was undertaken for 10 passes of 5 seconds each, with an interval of 5 seconds between each, and fresh irrigation with EDTA (Group A) or sterile saline solution (Group B) or sodium hypochlorite (Group C). A total of 50 sec. was the time of laser activity achieved to activate irrigants placed in controlled quantities (2ml), inside the root canals, in the 45 teeth of groups A, B and C. The 30 teeth of groups D and E were treated only with the irrigants, after a week of incubation and before of the bacterial count. Which irrigants were used: in group A 17% EDTA, in groups B and E, sterile saline solution; in groups C and D, 5.25% sodium hypochlorite. Then all the teeth were subjected to microbiological analysis and bacterial count by Colonies Forming Unit (CFU). Results: Average bactericidal effect obtained in group A (EDTA 17% + 50 sec. of laser activation) showed a bactericidal effect of 6.66 log mean CFU. The group B (sterile saline solution+ 50 sec. of laser activation) was 6.13 log mean CFU. The group C ( 5,25% sodium hypochlorite + 50sec of laser activation) showed the greatest reduction of bacteria with a 8 log mean CFU. The group E (sterile saline solution for 50 sec. without laser irradiation), presented the worst results with a bactericidal effect of 4.1 log mean CFU. A good result was also recorded in group D, that is characterized by the use of sodium hypochlorite without irradiation laser. Conclusion: The use of laser Er:Yag energy with a new conical optical fiber tip associated with sodium hypochlorite produces the same total sterility of the sodium hypochlorite solution used only after being experimentally infected. The use of fiber laser for 50 sec provides a statistically significant advantage in the groups treated with EDTA 17% or sterile saline solution. The use of laser Er: Yag 2940 nm providing a good bactericidal effect in the adopted experimental conditions.
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