The Functions of Saliva

Abstract

Nature's demands on salivary glands are extensive and diverse and range from the reptilian need for a venomous drop to incapacitate its prey to the 100 quarts that ruminants require to digest a day's grazing. Other species depend on saliva not for survival, but for improving the quality of life, using the fluid for functions varying from grooming and cleansing to nest-building. Humans can manage without saliva; its loss is not life-threatening in any immediate sense, but it results in a variety of difficulties and miseries. Oral digestion per se is only of marginal importance in humans, but saliva is important in preparing food for mastication, for swallowing, and far normal taste perception. Without saliva, mealtimes are difficult, uncomfortable, and embarrassing. The complex mix of salivary constituents provides an effective set of systems for lubricating and protecting the soft and hard tissues. Protection of soft tissues is afforded against desiccation, penetration, ulceration, and potential carcinogens by mucin and anti-proteases. Saliva can encourage soft tissue repair by reducing clotting time and accelerating wound contraction. A major protective function results from the salivary role in maintenance of the ecological balance in the oral cavity via : (1) debridement/lavage; (2) aggregation and reduced adherence by both immunological and non-immunological means; and (3) direct antibacterial activity. Saliva also possesses antifungal and anti-viral systems. Saliva is effective in maintaining pH in the oral cavity, contributes to the regulation of plaque pH, and helps neutralize reflux acids in the esophagus. Salivary maintenance of tooth integrity is dependent on: (I) mechanical cleansing and carbohydrate clearance; (2) post-eruptive maturation of enamel; (3) regulation of the ionic environment to provide a remineralizing potential without spontaneous precipitation; and (4) pellicle deposition and limitation of acid diffusion. Saliva also plays a role in water balance, can serve in a limited way in excretion, and has possible hormonal function in the gastro-intestinal tract.