Variables studied:> periodontal destruction (number of teeth, PPD, CAL, BoP)> presence of PeD bacteria in periodontium, serum, and CSF> periodontium and serum levels of IL-1β and MCP1/CCL2> serum and CSF IgG to PeD bacteria> CSF levels of Aβ1–42 and t-tauOutcome: AD (NIA-AA 2011 and MMSE). The gene discussed is CCL2; the disease is Alzheimer disease.