Xerostomia, also known as dry mouth, is a subjective complaint of dryness in the mouth, which may be associated with a change in the composition of saliva, reduced salivary flow, or have no identifiable cause.

This symptom is very common and is often seen as a side effect of many types of medication. It is more common in older people (mostly because individuals in this group are more likely to take several medications) and in people who breathe through their mouths. Dehydration, radiotherapy involving the salivary glands, chemotherapy and several diseases can cause reduced salivation (hyposalivation), or a change in saliva consistency and hence a complaint of xerostomia. Sometimes there is no identifiable cause, and there may sometimes be a psychogenic reason for the complaint. The term is derived from the Greek words ξηρός (xeros) meaning "dry" and στόμα (stoma) meaning "mouth". A drug or substance that increases the rate of salivary flow is termed a sialogogue.

Hyposalivation is a clinical diagnosis that is made based on the history and examination, An unstimulated whole saliva flow rate in a normal person is 0.3–0.4 ml per minute, and below 0.1 ml per minute is significantly abnormal. A stimulated saliva flow rate less than 0.5 ml per gland in 5 minutes or less than 1 ml per gland in 10 minutes is decreased. Research shows that enamel demineralization typically begins when oral pH drops below about 5.5, while root dentin, being more vulnerable, can start to erode at a higher pH of around 6.7. Many saliva substitutes and oral moisturizers are formulated with a pH below 6.7, which can pose a risk to dentin over time.

  • Acid erosion. Saliva acts as a buffer and helps to prevent demineralization of teeth.
  • Oral candidiasis – A loss of the antimicrobial actions of saliva may also lead to opportunistic infection with Candida species.
  • Saliva cannot be "milked" (expressed) from the parotid duct. During periods of stress, the human body responds in a 'fight or flight' state which interferes with the saliva flow in the mouth. Dehydration is known to cause hyposalivation,

Drug induced xerostomia

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! Table 1 - Medications associated with xerostomia

Radiation therapy

Radiation therapy for cancers of the head and neck (including brachytherapy for thyroid cancers) where the salivary glands are close to or within the field irradiated is another major cause of xerostomia.

Sicca syndrome

"Sicca" simply means dryness. Sicca syndrome is not a specific condition, and there are varying definitions, but the term can describe oral and eye dryness that is not caused by autoimmune diseases (e.g., Sjögren syndrome).

Other causes

Oral dryness may also be caused by mouth breathing, cannabis, hallucinogens, or heroin, may be implicated.

Hormonal disorders, such as poorly controlled diabetes, chronic graft versus host disease, or low fluid intake in people undergoing hemodialysis for renal impairment, may also result in xerostomia due to dehydration.

Xerostomia may be a consequence of infection with hepatitis C virus (HCV).

Diagnostic approach

A diagnosis of hyposalivation is based predominantly on the clinical signs and symptoms. The rate of the salivary flow in an individual's mouth can also be measured. There is little correlation between symptoms and objective tests of salivary flow, such as sialometry. This test is simple and noninvasive, and involves measurement of all the saliva a patient can produce during a certain time, achieved by dribbling into a container. Sialometery can yield measures of stimulated salivary flow or unstimulated salivary flow. Stimulated salivary flow rate is calculated using a stimulant such as 10% citric acid dropped onto the tongue, and collection of all the saliva that flows from one of the parotid papillae over five or ten minutes. Unstimulated whole saliva flow rate more closely correlates with symptoms of xerostomia than stimulated salivary flow rate. may be carried out if there is a suspicion of organic disease of the salivary glands. Both stimulants and substitutes relieve symptoms to some extent. Salivary stimulants are probably only useful in people with some remaining detectable salivary function.

A 2013 review looking at non-pharmacological interventions reported a lack of evidence to support the effects of electrostimulation devices, or acupuncture, on symptoms of dry mouth.

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Epidemiology

Xerostomia is a very common symptom. A conservative estimate of prevalence is about 20% in the general population, with increased prevalences in females (up to 30%) and the elderly (up to 50%). Estimates of the prevalence of persistent dry mouth vary between 10 and 50%.

See also

  • Xerosis (dry skin)

References

  • University of Illinois at Chicago
  • NIH
  • MedlinePlus Encyclopedia
  • Drymouth Drymouth Drug Database