Physical and Molecular Processes Controlling the Formation, Structure and Breakdown of the Salivary Pellicle
Objectives: Despite the importance of the pellicle in oral physiological and pathological processes, an understanding of the fundamental physical and molecular mechanisms underlying the structural formation and breakdown of this protein film remains unresolved. Therefore the work carried out herein attempts to elucidate the structural changes that the pellicle undergoes upon exposure to intrinsic and extrinsic factors. Such as; the role that mucins play in pellicle formation, the effect of a changing acidic environment or the structural changes that occur upon contact with dentifrice components. Methods: in vitro adsorbed pellicles were formed from the saliva (stimulated parotid saliva and stimulated whole mouth saliva) of 14 healthy volunteers, and studied using techniques including a quartz crystal microbalance with dissipation monitoring and a dual polarisation interferometer. The pellicles were then exposed to certain food and oral hygiene ingredients to observe the physical (e.g. surface mass, density, thickness and viscoelasticity) and chemical (e.g. protein composition) modifications that the pellicle undergoes when challenged in this way. Results: Mucins present in whole mouth saliva were shown to help form a more viscous pellicle compared to a pellicle formed from mucin free saliva (parotid saliva). Whereas, the pellicle formed from saliva containing 10 mM CaCl2 was more diffuse and less stable compared to pellicles formed from saliva containing 1mM CaCl2. Structural changes in the pellicle also took place upon exposure to pH4 and pH3 3 citrate buffers, changes that may be related to the isoelectric points of the proteins present in the pellicle. Finally, the polyanionic STP molecule was shown to be more effective than SDS at displacing pellicle form hydroxyapatite. Conclusion: This research demonstrated that the composition of saliva has an important effect on the physical properties of the adsorbed pellicle; and lays the foundations as to how regulating the calcium concentration of saliva provides a mechanism that can control the physical properties of the in-vitro formed pellicle. In addition, the structural changes that the pellicle undergoes under differing acidic environments, and upon exposure to components of oral hygiene products, were observed to help understand the mechanisms underlying the formation and breakdown of the salivary pellicle.
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