Xerostomia, also known as dry mouth, is dryness in the mouth, which may be associated with a change in the composition of saliva, or 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 this group tend to take several medications) and in persons who breathe through their mouths (mouthbreathing). Dehydration, radiotherapy involving the salivary glands, chemotherapy and several diseases can cause hyposalivation or a change in saliva consistency and hence a complaint of xerostomia. Sometimes there is no identifiable cause, and there may be a psychogenic reason for the complaint.
Xerostomia is the subjective sensation of dry mouth, which is often (but not always) associated with hypofunction of the salivary glands. 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, but reduced salivary flow rates have been given objective definitions. Salivary gland hypofunction has been defined as any objectively demonstrable reduction in whole and/or individual gland flow rates. 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. The term subjective xerostomia is sometimes used to describe the symptom in the absence of any clinical evidence of dryness . Xerostomia may also result from a change in composition of saliva (from serous to mucous). Salivary gland dysfunction is an umbrella term for the presence of either xerostomia or salivary gland hypofunction.
A diagnosis of hyposalivation is based predominantly on the clinical signs and symptoms. Although dry mouth can not be measured and is subjective to personal expression, the rate of the salivary flow in an individual’s mouth can 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. Sialography involves introduction of radio-opaque dye such as iodine into the duct of a salivary gland. It may show blockage of a duct due to a calculus. Salivary scintiscanning using technetium is rarely used. Other medical imaging that may be involved in the investigation include chest x-ray (to exclude sarcoidosis), ultrasonography and magnetic resonance imaging (to exclude Sjögren’s syndrome or neoplasia). A minor salivary gland biopsy, usually taken from the lip, may be carried out if there is a suspicion of organic disease of the salivary glands. Blood tests and urinalysis may be involved to exclude a number of possible causes. To investigate xerophthalmia, the Schirmer test of lacrimal flow may be indicated. Slit-lamp examination may also be carried out.
The successful treatment of xerostomia is difficult to achieve and often unsatisfactory. This involves finding any correctable cause and removing it if possible, but in many cases it is not possible to correct the xerostomia itself, and treatment is symptomatic, and also focuses on preventing tooth decay through improving oral hygiene. Where the symptom is caused by hyposalivation secondary to underlying chronic disease, xerostomia can be considered permanent or even progressive. The management of salivary gland dysfunction may involve the use of saliva substitutes and/or saliva stimulants:
Saliva substitutes – These are viscous products which are applied to the oral mucosa, which can be found in the form of sprays, gels, oils, mouthwashes, mouth rinses, pastilles or viscous liquids. This includes SalivaMAX, water, artificial salivas (mucin-based, carboxymethylcellulose-based), and other substances (milk, vegetable oil):
Mucin Spray: 4 Trials have been completed on the effects of Mucin Spray on Xerostomia, overall there is no strong evidence showing that Mucin Spray is more effective than a placebo in reducing the symptoms of dry mouth.
Mucin Lozenge: Only 1 trial (Gravenmade 1993) has been completed regarding the effectiveness of Mucin Lozenges. Whilst it was assessed as being at high risk of bias, it showed that Mucin Lozenges were ineffective when compared to a placebo.
Mucoadhesive Disk: These disks are stuck to the palate and they contain lubricating agents, flavouring agents and some antimicrobial agents. One trial (Kerr 2010) assessed their effectiveness against a placebo disk. Strangely, patients from both groups (placebo and the real disk) reported an increase in subjective oral moistness. No adverse effects were reported. More research is needed in this area before conclusions are drawn.
Biotene oral Balance Gel & toothpaste: One trial has been completed (Epstein 1999) regarding the effectiveness of Biotene Oral Balance gel & toothpaste. The results showed that Biotene products were “more effective than control and reduced dry mouth on waking”.
Saliva stimulants – organic acids (ascorbic acid, malic acid), chewing gum, parasympathomimetic drugs (choline esters, e.g. pilocarpine hydrochloride, cholinesterase inhibitors), and other substances (sugar-free mints, nicotinamide). Medications which stimulate saliva production traditionally have been administered through oral tablets, which the patient goes on to swallow, although some saliva stimulants can also be found in the form of toothpastes. Lozenges, which are retained in the mouth and then swallowed are becoming more and more popular. Lozenges are soft and gentle on the mouth and there is a belief that prolonged contact with the oral mucosa mechanically stimulates saliva production.
Pilocarpine: A study by Taweechaisupapong in 2006 showed no ‘statistical significant improvement in oral dryness and saliva production compared to placebo’ when administering pilocarpine lozenges.
Physostigmine Gel: A study by Knosravini in 2009 showed a reduction in the oral dryness and a 5 times increase in saliva following physostigmine treatment.
Chewing gum increases saliva production but there is no strong evidence that it improves dry mouth symptoms.
The Cochrane oral health group concluded ‘there is insufficient evidence to determine whether pilocarpine or physostigmine’ are effective treatments for Xerostomia. More research is needed.
Dentirol chewing gum (xylitol): A study by Risheim in 1993 showed that when subjects had 2 sticks of gum up to 5 x daily, the gum gave subjective dry mouth symptom relief in approximately 1/3 of participants but no change in SWS (stimulated whole saliva).
Profylin lozenge (xylitol/sorbitol):A study by Risheim in 1993 showed that when subjects had 1 lozenge 4 to 8 x daily, profylin lozenges gave subjective dry mouth symptom relief in approximately 1/3 of participants but no change in SWS (stimulated whole saliva).
Saliva substitutes can improve xerostomia, but tend not to improve the other problems associated with salivary gland dysfunction. Parasympathomimitic drugs (saliva stimulants) such as pilocarpine may improve xerostomia symptoms and other problems associated with salivary gland dysfunction, but the evidence for treatment of radiation-induced xerostomia is limited. Both stimulants and substitutes relieve symptoms to some extent. Salivary stimulants are probably only useful in people with some remaining detectable salivary function. A systematic review compromising of 36 randomised controlled trials for the treatment of dry mouth found that there was no strong evidence to suggest that a specific topical therapy is effective. This review also states that topical therapies can be expected to provide only short-term effects, which are reversible. The review reported limited evidence that oxygenated glycerol triester spray was more effective than electrolyte sprays. Sugar free chewing gum increases saliva production but there is no strong evidence that it improves symptoms. Plus, there is no clear evidence to suggest whether chewing gum is more or less effective as a treatment. There is a suggestion that intraoral devices and integrated mouthcare systems may be effective in reducing symptoms, but there was a lack of strong evidence. A systematic review of the management of radiotherapy-induced xerostomia with parasympathomimetic drugs found that there was limited evidence to support the use of pilocarpine in the treatment of radiation-induced salivary gland dysfunction. It was suggested that, barring any contraindications, a trial of the drug be offered in the above group (at a dose of five mg three times per day to minimize side effects). Improvements can take up to twelve weeks. However, pilocarpine is not always successful in improving xerostomia symptoms. The review also concluded that there was little evidence to support the use of other parasympathomimetics in this group. Another systematic review showed, that there is some low-quality evidence to suggest that amifostine prevents the feeling of dry mouth or reduce the risk of moderate to severe xerostomia in people receiving radiotherapy to the head and neck (with or without chemotherapy) in the short- (end of radiotherapy) to medium-term (three months postradiotherapy). But, it is less clear whether or not this effect is sustained to 12 months postradiotherapy.
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.
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% .
Xerostomia has been used as a test to detect lies, which relied on emotional inhibition of salivary secretions to indicate possible incrimination.