Singlet oxygen generated by a new nonthermal atmospheric pressure air plasma device exerts a bactericidal effect on oral pathogens

Oral diseases generally have certain bacteria associated with them. Non-thermal atmospheric pressure plasma (NTAP), generated at atmospheric pressure and room temperature, incorporates several molecules, including reactive oxygen species, that can inactivate various bacteria including oral pathogens. For this reason, several NTAP devices have been developed to treat oral diseases. Use of noble gases can enhance the bactericidal efficacy of NTAP, but this requires additional gas supply equipment. Therefore, a new NTAP device that employs ambient air as the working gas was developed. The device generates non-thermal atmospheric pressure air plasma. Here, the singlet oxygen (O-1(2)) levels generated, their bactericidal effects on oral pathogens (Streptococcus mutans, Porphyromonas gingivalis, and Enterococcus faecalis), and the bacterial oxidative stress they imposed were measured. O-1(2) generation in phosphatebuffered saline was assessed qualitatively using electron spin resonance (ESR) spectroscopy, and bactericidal efficacy was evaluated by counting of colony-forming units/mL. Bacterial oxidative stress was determined by measurement of hydrogen peroxide (H2O2) and superoxide dismutase (SOD) activity. ESR indicated that the level of O-1(2) increased significantly and time-dependently, and was inversely correlated with distance, but the bactericidal effects were correlated only with treatment time (not distance) as H2O2 increased and SOD levels decreased, suggesting that the new device has potential applicability for treatment of oral disease.