ROS play an important role in the pathomechanism of periodontitis.Gram-negative anaerobes colonizing dental plaque trigger the recruitment and activation of neutrophils, which subsequently produce a range of antimicrobial factors during phagocytosis of periodontal pathogens and release an excess of ROS through the NADPH oxidase pathway (130, 131). The gene discussed is FMO5; the disease is periodontitis.