Effect of Oral Health Ingredients on the Acquired Salivary Pellicle

Saliva contains many proteins and components that contribute to film formation, and we know that saliva forms complex, structured films on surfaces. The mucosal salivary layer, comprises of a mobile layer of saliva and an immobile film of salivary proteins adsorbed onto oral epithelial cells, the "mucosal pellicle". The salivary film is thin (10-100 µm), extremely viscoelastic and aids lubrication, influences the sensory perception of food in the mouth and maintains oral health. The apparent viscoelastic and coating properties of saliva are in fact mainly due to the formation of an incredibly strong, viscoelastic film at surfaces and interfaces. The solution viscosity of saliva is actually close to that of water at high shear rates, but the interfacial viscosity is more than 10,000 times greater than water, which completely dominates the physical properties of the salivary film as a whole. This complex structure is driven by molecular scale interactions and is thought to be responsible for the film forming properties of saliva. What is still unclear are the fundamental physical and molecular mechanisms underlying the film forming properties of saliva. Although the viscous and lubricating properties of saliva have often been assigned to mucins, it appears that isolated mucins do not impart the same lubrication properties as they do in whole saliva. Other proteins such as statherin have been implicated in enhancing boundary lubrication. The molecular composition of salivary proteins and the presence of ions appear to be all important in forming the salivary film. For example, parotid saliva which contains no mucin is still highly lubricating probably due to its highly visco-elastic surface layer.

The mucosal pellicle can be mimicked in vitro by adsorbing salivary proteins onto model surfaces to form interfacial films and has been shown to be highly lubricating. The presence of polyphenols has been shown to reduce the lubricity of these surface films and correlate well with their sensory properties. At the Quadram Institute Bioscience (QIB) we have over 20 years' experience studying proteins at interfaces and surfaces, in particular how competitive adsorption at interfaces of proteins with surfactants and other surface-active components can affect the composition, structure and stability of the interface, and how this controls the functionality of the system as a whole. This was applied in a collaborative study on interfacial salivary films with Kings College London, where we demonstrated the highly visco-elastic nature of the salivary film and the critical importance of calcium ions in its formation.

Leading up to this project, the recent postgraduate (PhD) student project at QIB demonstrated that added calcium can strengthen the salivary pellicle, and that the formation of the pellicle was a two stage process involving small, surface active proteins in the primary stage, and larger mucin proteins in the later stage. The study also demonstrated that reducing pH reduced the integrity of the pellicle, which helps us to understand the role of the pellicle in preventing acid erosion, and that the addition of various active ingredients from toothpaste and mouthwash would remove certain proteins from the pellicle, depending on the type of active ingredient and the surface on which the pellicle was formed. We would like to extend this project to look at how these active ingredients in mouthwash and toothpaste affect the structure of the pellicle, and if any combinations of these ingredients have any additional effect.

Therefore our hypothesis is that active ingredients from toothpastes and mouthwashes can be used to control the structure of the salivary pellicle through their interactions with either the surface that the pellicle is adsorbed to, or with the proteins in the pellicle itself.

Understanding these changes to the structure and properties of the salivary film could then help us understand how the pellicle and the active ingredients protect teeth against decay and disease.