The Prevalent Dry Mouth Syndrome
Xerostomia, commonly called dry mouth, is a condition of oral dryness. In many, but not all cases, it is caused by reduced or absent saliva flow due to impaired salivary gland function. While oral dryness may not sound serious, xerostomia can in fact be a contributing factor in a number of oral health problems, including increased risk of plaque, tooth demineralization, dental caries, dental erosion, oral yeast infections, and ulcers of the tongue.1,2
Saliva: A Quick Review
Saliva is secreted from the parotid, submaxillary, sublingual and minor mucous glands of the mouth. Healthy saliva is viscous, clear, and watery. It contains two types of protein secretions: a serous secretion that contains the digestive enzyme ptyalin, and a mucous secretion that contains a lubricating fluid called mucin. Saliva also contains potassium, bicarbonate, chloride, and sodium ions that help remineralize teeth, as well as a number of antimicrobial agents, such as lysozymes, lactoferrins, and immunoglobins.3,4
Salivary function is mediated primarily by receptors that are located in the salivary glands (Figure 1). When these receptors are stimulated, flow of saliva increases.4 Many of the medications that have been linked to xerostomia hinder function of these receptors, reducing salivary production and volume.
Common Causes of Xerostomia
More than 400 commonly prescribed drugs in the United States can cause xerostomia.3,5 Some medications—such as sedatives, antidepressants, antihistamines, opiates, antipsychotics, anti-Parkinson agents, and antianxiety agents—interfere with the function of salivary gland receptors, reducing salivary production and volume.3,5
Others, such as antihypertensives and diuretics, interfere with the body's salt, water, and electrolyte balance. This changes the composition of saliva so it contains less of the lubricating agent mucin, as well as low concentrations of ions needed in remineralization. Polypharmacy—taking multiple medications everyday—has also been associated with dry mouth, with the risk being the highest when more than three different drugs are taken daily.3,5
Cancer treatments, such as chemotherapy, or radiotherapy to the head and neck, can also cause dry mouth if the treatment has affected salivary glands. Sometimes affected salivary glands maintain some functional ability, but sometimes cancer treatments can destroy them completely.6
Systemic Diseases and Other Health Conditions
A number of systemic diseases have been linked to impairments in saliva secretion or compositional changes in saliva. These include autoimmune diseases such as Sjögren's syndrome, rheumatoid arthritis, autoimmune thyroiditis, and systemic lupus erythematosus; chronic infections such as hepatitis C virus (HCV) and human immunodeficiency virus (HIV); and hormonal conditions such as diabetes or menopause.3,7
Other conditions that have been implicated in dry mouth include eating disorders such as bulimia or anorexia nervosa; neurological disorders such as depression, bipolar disorder, Bell's palsy, or cerebral palsy; and local salivary diseases such as salivary gland cancer, salivary duct stones, or salivary gland infections.3,7 Chronic use of alcohol and other drugs, such as cannabis and methamphetamines, have also been linked to xerostomia.3,7-9
Who Is Most at Risk?
The elderly tend to be most at risk for dry mouth. This isn't because age itself causes the condition, but rather because this age group is more likely to have systemic diseases and health conditions linked to xerostomia. The elderly are also more likely to be taking medications, and engaged in polypharmacy.3
Particular attention should also be paid to women between the ages of 40 and 60, since they are undergoing hormonal changes as they transition to menopause that affect salivary gland function, inducing dry mouth.10 This group is also most at risk for the autoimmune condition Sjögren's syndrome (SS), the most common disease that causes xerostomia. In SS, the body's immune system attacks secretory glands (such as the salivary glands and tear glands), so they lose their ability to produce sufficient lubricating fluid. This causes dryness of all mucosal linings of the body, including the mouth, eyes, and digestive tract.3,7,11
Medications to Help Patients Manage Dry Mouth
While the ideal scenario is one in which you could help a patient identify the underlying cause of dry mouth and take steps to minimize the cause, this may not always be possible. In addition to helping patients manage their symptoms with the tips recommended above, some may benefit from medications that substitute saliva or increase salivary flow.
Over-the-counter saliva substitutes are products that mimic saliva to replace moisture, and make the mouth feel more lubricated. Many are also formulated to supply calcium, phosphate, and fluoride ions, to counteract the demineralization and increased caries risk that accompanies dry mouth. Studies have found that they also help decrease plaque levels, and reduce gingivitis and oral yeast infection risk.13 These come in the form of sprays, lozenges, or mouthwashes.
Another type of medication that may help some patients with dry mouth—depending on if their salivary glands are still able to function—is a salivary stimulant. These include over-the-counter lozenges and tablets; and prescription medications, such as pilocarpine and cevimeline, which activate the receptors to increase saliva production.14
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