RESUMEN
The mouth is a complex natural cavity which constitutes the initial segment of the digestive tract. It is an essential actor of the vital functions as nutrition, language, communication. The whole mouth (teeth, periodontium, mucous membranes, tongue) is constantly hydrated and lubricated by the saliva. At any age, a balance becomes established between the bacterial proliferations, the salivary flow, the adapted tissular answer: it is the oral ecosystem. The regulation of this ecosystem participates in the protection of the oral complex against current inflammatory and infectious pathologies (caries, gingivitis, periodontitis, candidiasis). In elderly, the modification of the salivary flow, the appearance of specific pathologies (root caries, edentulism, periodontitis), the local conditions (removable dentures), the development of general pathologies, the development of general pathologies (diabetes, hypertension, immunosuppression, the insufficient oral care are so many elements which are going to destabilize the oral ecosystem, to favor the formation of the dental plaque and to weaken oral tissues. The preservation of this ecosystem is essential for elderly: it allows to eat in good conditions and so to prevent the risks of undernutrition. The authors describe the oral physiopathology (oral microflora, salivary secretion) and the strategies to be adopted to protect the balance of the oral ecosystem in geriatric population.