The ROS production levels in blue light-irradiated P. gingivalis were measured with CellROX® Green Reagent (Promega Corporation, Madison, WI, USA). The washed P. gingivalis was adjusted to an optical density of 0.6 at 550 nm. P. gingivalis was suspended in PBS with 20 µM CellROX® Green Reagent and placed into a 96-well plate at 150 µL per well and irradiated for 0, 1, 10, or 100J. Non-target wells were covered with aluminum foil. After irradiation, the entire 96-well plate was covered with aluminum foil and incubated for 30 min at room temperature. The fluorescence intensity was measured with an infiniteM200 (Tecan Group Ltd., Männedorf, Switzerland) connected to PLATEmanagerV5 (Wako Pure Chemical Industries, Ltd., Osaka, Japan) at an excitation wavelength of 485 nm and an emission wavelength of 520 nm.