15. Salivary and taste complications

Saliva is essential to oral health. Low salivary flow (hyposalivation) causes lack of mucosal wetting, lubrication and defences, which affects many functions, and can predispose to infections.

Hyposalivation is not synonymous with Xerostomia.

Salivary secretion is controlled via neurotransmitters under the influence of the autonomic nervous system, although various hormones may also modulate salivary composition. In general, parasympathetic stimulation increases secretion as a result of activation of acinar cell M3 muscarinic receptors; sympathetic stimulation also produces more saliva – via alpha 1 adrenergic receptors, though much less than occurs following muscarinic stimulation. Water-specific channels, or aquaporins (AQPs) facilitate water movement across acinar cell plasma membranes, and provide the fluid secretion in salivary glands. Stimulation via beta adrenergic receptors stimulates protein release from acinar cells. The neuropeptides substance p and vasoactive intestinal peptide (VIP), as well as autocoids (histamine and bradykinin) may also influence salivary secretion.

Radiotherapy (RT) involving the salivary glands readily causes hypofunction. The main other causes of hyposalivation are drugs (cytotoxics and those with anticholinergic or sympathomimetic activity), Sjögren's syndrome, diabetes, HIV disease, sarcoidosis, and dehydration.