It has been established that saliva plays a crucial role in reducing caries risk. This is due in large part to saliva’s physical, chemical and antibacterial properties.
Physical Protective Qualities
Due to its water content and flow rate, saliva physically cleanses the oral cavity of food and debris.12 Unstimulated flow rates are approximately 0.3 to 0.4 ml/min, while stimulated flows are approximately 1.5 to 2 ml/min, although there are wide variations between individuals.9 Most humans produce roughly 0.5 to 1 liter of saliva per day with 90% secreted from the major glands. Saliva also dilutes and removes organic acids from dental plaque.12
Chemical Protective Qualities
Saliva contains a number of electrolytes and organic molecules that minimize decreases in local pH, creating an environment that favors remineralization. For example, sodium bicarbonate and phosphates, along with other salivary components, act as buffers or neutralizing agents in saliva. In addition, one salivary protein called sialin tends to raise salivary pH to neutral levels.
Saliva is also supersaturated with hydroxyapatite, fluorapatite, and calcium and phosphate ions compared to the carbonated hydroxyapatite in enamel. This supersaturation is maintained by the proline-rich proteins and statherins in saliva, and it increases the likelihood of remineralization via the incorporation of calcium and phosphate into enamel.9,10
Saliva contains several proteins with different types of antibacterial properties: The mucins are sulfated glycoproteins that trap, aggregate, and clear bacteria. The enzymes called amylases break down food particles that stick to teeth, reducing the bacterial build-up that can lead to decay.
Lysozyme is a cationic protein that lyses (damages) the cell walls of bacteria, rendering them inactive. Lactoferrin is an iron-binding glycoprotein that deprives bacteria of energy-generating iron so that they cannot survive. Peroxidase enzyme is a protein that forms free radical compounds in bacterial cells which cause them to self-destruct.14 Immunoglobulins are antigen-binding proteins that block the adherence of bacteria to the tooth surface and/or promote the clearance of bacteria from tooth structure.