Xerostomia is a chronic sensation of dry mouth. It is due to a qualitative and/or quantitative dysfunction of saliva production. Various factors related to ageing and health status can influence the quantity and quality of saliva produced. From a physical point of view, the decrease in salivary flow and/or the alteration of saliva results in a modification of the tribological mechanisms of the tongue-saliva couple. These clinical manifestations generate friction on the oral mucous membranes responsible for pain, burning sensations, speech difficulties and dysphagia. At present, there is no device allowing the objective measurement and characterisation of the lubrication of the oral cavity in vivo in humans, for the understanding, diagnosis and follow-up of the treatment of xerostomia, particularly for the relevance of the use of salivary substitutes. The approaches developed are essentially in vitro and in rare cases ex vivo. The BIOTRIBOSALIVE project aims to propose a new method of in vivo measurement of lubrication in the mouth of the tongue-saliva pair. This project addresses a new and fundamental answer in the in vivo understanding of oral lubrication. It considers for the first time the role of bio-physical (mucin levels and types, proteins, viscoelasticity, physicochemistry) and bio-tribological in vivo parameters (friction, vibration, salivary flow, tongue roughness) of the saliva-tongue pair in the study of dry mouth. The results of this work will allow the development of a new methodology for the quantitative analysis of xerostomia, thus enabling clinicians and patients to better monitor and evaluate this pathology.