They considered that periodontitis leads to the release of proinflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor into systemic circulation, and that psychological stress in patients with periodontitis promotes disturbances in the hypothalamic–pituitary–adrenal (HPA) axis and related hypercortisolism. This evidence concerns the gene TNF and periodontitis.