Oral medicine: 4. Dry mouth and disorders of salivation.

Saliva is essential to oral health. The most obvious and important function of saliva is in eating, for taste and to lubricate food, as well as protecting the mucosa and teeth (Table 1). The water, mucins and proline-rich glycoproteins lubricate food and help swallowing. Importantly, saliva is essential for normal taste perception. Saliva is protective via the washing action, via various antimicrobial components such as mucin, histatins, lysozyme and lactoferrin, and via specific antibodies to a range of micro-organisms that the host has encountered. Salivary gland secretion from the major (parotid, submandibular and sublingual) and minor glands (multiple mucous glands scattered throughout the mouth – especially the lips and soft palate), is mainly under neural control, under the influence of the autonomic nervous system, although various hormones may also modulate its composition. In general, parasympathetic stimulation increases salivation, while sympathetic stimulation produces more viscous saliva and therefore appears to depress salivation. Thus, in acute anxiety, when there is sympathetic stimulation, the mouth feels dry. The mouth is also dry if the parasympathetic system is inhibited by, for example, various drugs. Anything that damages the glands, or reduces body fluids, can also reduce salivation.