Inclusion Criteria:  Age greater than or equal to 70 years old Patient (or trusted person) having read and understood the study information note and signed the informed consent form Membership in a social security scheme For cases : Diagnosis of possible or probable Alzheimer's disease according to the DSM-V  Exclusion Criteria:  Presence of a neurodegenerative pathology (excluding Alzheimer's disease for cases) Presence of a neurocognitive disorder (excluding Alzheimer's disease for the cases) Patient with or having had any kind of cancer, including oral or aerodigestive tract Patients with or having had autoimmune diseases (HIV, hepatitis) Patients with inflammatory diseases (such as rheumatoid arthritis (RA) or Gougerot-Sjogren's syndrome (GSJ)) Patients with severe haemopathy Patients with severe acute or chronic cardiovascular, renal, hepatic, gastrointestinal, allergic, endocrine, pulmonary, neuropsychiatric pathologies, judged by the investigator to be incompatible with the study, as all these pathologies may interfere with the results of the oral flora sampling Patients who have undergone oral surgery in the two months prior to sampling Patients treated with oral retinoids, bisphosphonates, oral anticoagulants or anticonvulsants Patients who have had anti-cancer or immunosuppressive chemotherapy within the last 6 months Patient who has had antibiotic or anti-inflammatory treatment in the last 4 weeks A history of treatments (drugs and probiotics) taken in the month prior to sampling will be taken, as well as a record of toxic habits (tobacco, alcohol, other)