TNF and periodontitis: Experimental chronic periodontitis, induced by repeated oral application of another live P. gingivalis W83 every 48 h over 22 weeks, has been demonstrated to increase extracellular Aβ42 amyloid plaques, ser396 residue of tau protein phosphorylation, neurofibrillary tangle formation, and neuroinflammation (i.e., microglial activation, astrocytic activation, and increased expression of TNF-α, IL-1β and IL-6) in the hippocampus of 6-week old mice [47].