Study of the direct bactericidal effect of Nd:YAG and diode laser parameters used in endodontics on pigmented and nonpigmented bacteria |
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Authors: | Samo Pirnat Matjaz Lukac Alojz Ihan |
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Institution: | (1) Faculty of Medicine, Institute of Microbiology and Immunology, University of Ljubljana, Zaloska 4, 1000 Ljubljana, Slovenia;(2) Light and Matter Department, Institute Jozef Stefan, Jamova 19, 1000 Ljubljana, Slovenia |
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Abstract: | Laser light can be used during endodontic procedures to sterilize the root canal by destroying bacteria. Previous in-vitro
studies that investigated the mechanism of the destruction of bacteria inhabiting the root canal by 1,064-nm Nd:YAG and 808-nm
diode laser light used substrates that absorb light in the near-infrared (NIR) spectrum. These substrates heat the bacterial
microenvironment, which possibly contributes to cell death. To determine the direct effect of laser light on the bacterial
sample in the absence of detrimental heating, a sapphire substrate, which is virtually transparent in NIR spectrum, was inoculated
with bacterial samples and subjected to laser irradiation at 1,064 nm (1.5 W, 15 Hz) and at 808 nm (1.5 W, 20 Hz). Enterococcus faecalis, Escherichia coli, and Porphyromonas gingivalis bacteria were used. E. faecalis and E. coli were largely unaffected by laser light. The viability of P. gingivalis, a pigmented bacterium, was directly affected by both NIR wavelengths (a 57% decrease of viability at 1,064 nm and a 31%
decrease at 808 nm). Our results indicate that the primary mediator of cell death appears to be the interaction between NIR
laser light and the bacterial microenvironment, most likely in the form of heating. Our research suggests that when optimizing
the efficacy of laser-assisted endodontic sterilization of the root canal, the optical characteristics of the bacterial microenvironment
play a key role, as nonpigmented bacteria appear to be virtually transparent at 808 nm and 1,064 nm. |
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