Similarly, prostaglandin E2 (PGE2) released by macrophages and oxidative stress induced by neutrophils can cause more release of proinflammatory cytokines such as TNF‐α, IL‐1β, and IL‐6 and matrix metalloproteinases (MMPs) such as MMP-1, MMP-2, MMP-8, MMP-9, and MMP-13, which lead to local degradation of collagen fibers, loss of periodontal attachment, and resorption of alveolar bone, promote the progression of periodontitis, and enlarge inflammatory response and periodontal tissue (153–157). Here, TNF is linked to periodontitis.