Saliva Function and Production

Composition of Saliva

• Whole mouth saliva consists of biofilm, enamel/dentine, GCF (Gingival Crevicular Fluid), shed epithelial cells, and transudate
• Acinus produces salivary fluid containing water, electrolytes, blood proteins, and salivary proteins
• Ducts produce Na+, Cl-, and glandular salivas

Cells, Microorganisms, and Microparticles in Saliva

• Cells in saliva include epithelial cells and neutrophils
• Microorganisms in saliva include bacteria (10^8/ml), viruses, candida, and protozoa
• Microparticles in saliva include exosomes (increased flow and oral clearance)

Functions of Saliva

• Buffers pH and maintains enamel pellicle
• Protects and maintains oral mucosa through wound healing, lubrication, and barrier formation
• Regulates oral microbiota through clearance, killing, and agglutination of pathogens, and colonization, adhesion, and feeding of commensals
• Aids in taste and processing of food/nutrients

Flow Rate and Oral Clearance

• Very low salivary flow rate increases the risk of dental caries
• Buffering in saliva by bicarbonate involves the reaction: CO2 + H2O → H2CO3 → HCO3- + H+

Acquired Enamel Pellicle

• A thin layer (<1 μm) formed by calcium-binding salivary proteins (statherin, histatins, and acidic proline-rich proteins)
• Prevents surface mineralization and enhances sub-surface remineralization
• Lubrication reduces friction by 20-fold

Saliva and Tooth Mineralization

• Tooth apatite (Ca10(PO4)6OH2) is dependent on supersaturation of saliva with calcium and phosphate
• Concentration of Ca2+ in resting saliva is approximately 2mM
• Supersaturation of saliva with calcium and phosphate is due to salivary protein statherin

Saliva and Oral Mucosa

• Saliva forms a hydrated, barrier film on the oral mucosa
• Lubrication, barrier function, and interaction with the mucosal surface are essential
• Saliva regulates oral microorganisms by clearing microorganisms, modifying the adherence of microorganisms to teeth, and modulating microbial growth

Anti-Microbial Factors in Saliva

• Saliva contains anti-bacterial proteins (cystatins, histatins, defensins, cathelicidins, lysozyme, lactoferrin, lactoperoxidase, SLPI, chromogranin A, PLUNCs, immunoglobulins, mucins)
• Saliva also contains anti-fungal and anti-viral proteins

Summary

• Saliva enables oral tissues to cope with a range of problems associated with oral functions
• Resting (unstimulated) flow of saliva is crucial for oral health
• Submandibular and sublingual glands contribute the most to resting flow rate, while parotid glands contribute more to stimulated flow rate
• Saliva forms films and pellicles on hard and soft tissues in the mouth