Additionally, ligature-induced acute periodontitis in the molar region causes neuroinflammation and cognitive decline through the STAT3 signaling pathway [37], and ligature-induced periodontal disease-associated microbiome increases activation of microglial cells and enhances phagocytosis of amyloid β via the TLR2/TLR9-mediated pathway [38]. This evidence concerns the gene TLR9 and periodontal disorder.