Lubrication of soft oral surfaces

Oral lubrication deals with one of the most intricate examples of biotribology, where surfaces under sliding conditions span from the hardest enamel to soft oral tissues in human physiology. Complexity further arises with surfaces being covered by an endogenous biolubricant saliva before exogenous food particles can wet, stick, or slip at the surfaces. In this review, we present a description of soft oral surfaces, comparing them with the recent approaches that have been used to study oral lubrication using in vitro to ex vivo setups. Specifically, lubrication behaviors of saliva and soft microgels are discussed highlighting instances of hydration lubrication. We have structured this information creating a strong link between theoretical concepts and oral lubrication, which has thus far remained elusive in literature. Finally, we highlighted some of the several challenges remaining in this field and discussing how emerging technologies in material science might help overcoming them.