Bactericidal effect of 445-nm blue diode laser in the root canal dentin on Enterococcus faecalis of human teeth

Objectives: The objective of this in vitro study was to determine the bactericidal effect of a blue diode laser with a wavelength of 445 nm in dentin slices of human teeth. Materials and methods: A total of 81 dentin slices (longitudinal section) with different thicknesses of (300, 500, and 1000 μm) were used in this study. The dental slices were divided into three laser test groups and four control groups (positive and negative). All (except the negative control groups) were inoculated with a suspension of Enterococcus faecalis (2.0 × 107 CFU/ml). The tested groups were subjected to different irradiation parameters: group I (1.2 W peak power, 0.6 W average power), group II (0.6 W, CW), and group III (0.4 W, CW). The irradiation was performed using a bare fiber with a diameter of 200 μm at an angulation of approximately 5° to the slice under constant sinus-shaped movement of the slice. Identical irradiation conditions were applied using a computer-controlled table. This appliance allowed to move the slices in a sinusoidal motion in a constant velocity during irradiation. Results: The results of this in vitro study showed the irradiation with a chopped mode of 1.2 W eliminated an average of 96%, 97.6%, and 84.9% of E. faecalis at dentin depths of 300 μm, 500 μm, and 1000 μm, respectively. The irradiation with continuous mode 0.6 W eliminated 82.41% (300 μm), 83.75% (500 μm), and 77.42 (1000 μm). Whereas, lower power 0.4 W in continuous mode eliminated 6.90%, 32.50%, and − 9.68% at dentin depths of 300 μm, 500 μm, and 1000 μm, respectively. Conclusion: No statistical but conspicuous difference was found between group I and group II in all dentin slice thicknesses, with p = 0.067 (p > 0.05), whereas the bacterial counts in groups I and II compared to group III were significantly different with p values as p = 0.002 and p = 0.01 (p < 0.05) respectively. Reducing the power in continuous mode had decreased the antibacterial effect of this laser. © 2018, Springer Nature Switzerland AG.