Xerostomia—or dry mouth—is an increasingly prevalent disorder that adversely affects the quality of life of those who suffer from it. We can help patients prevent and treat xerostomia at the dental clinic by taking various measures and applying different treatments to help moisturise the oral cavity and stimulate saliva secretion. 

Xerostomia is the subjective feeling of a dry mouth. It is usually associated with hyposialia—reduced saliva secretion—but this is not always the case, since it can also be induced by other factors, such as changes in the biochemical composition of the saliva. It is therefore necessary to differentiate between xerostomia (the subjective sensation of a dry mouth) and hyposialia (the objective decrease in saliva secretion). 

The prevalence of xerostomia is high and can range from 20% in adults between the ages of 18 to 35 years to more than 40% in adults over 55. This prevalence is increasing due to longer life expectancy and an increase in the use of potentially xerostomising medication, amongst other factors. 

Xerostomia patients may have difficulty chewing, swallowing, or speaking, symptoms that significantly affect their quality of life. In addition, saliva has numerous protective properties for the mouth: antimicrobial functions, oral pH buffering effect, lubrication and moisturising of oral tissues, contribution to the remineralisation of enamel and dentin, etc. Therefore, a reduction in saliva flow can adversely affect oral health. 

Saliva production is regulated by the autonomic nervous system (ANS), which is, in turn, divided into the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSNS). Normally, the SNS and the PSNS exert opposite actions, except in the ciliary muscle and in the salivary glands. Thus, stimulation of the PSNS produces abundant serous saliva, while if the SNS is stimulated, saliva production increases slightly, and saliva is predominantly mucous. Inhibition of the SNS and/or the PSNS leads to a decrease in saliva production. 

It is important to be aware of these mechanisms in order to understand the possible causes of alterations in saliva production. 

CAUSES OF XEROSTOMIA 

Local factors 

Local factors are those that directly affect the salivary glands, either in their anatomy or their physiology and innervation. The following local factors may be encountered: 

• Use of medication. There are more than 500 medicines — 80% of those most prescribed — that may have xerostomia as a side effect, since they impact on the nervous regulation of the salivary glands. These medicines include anticholinergics — by their inhibitory action on the PSNS, antihypertensives, antidepressants, anxiolytics, sedatives, antiparkinsonians, antihistamines, bronchodilators, antimigraine agents, anti-inflammatories, analgesics, etc. Ultimately, the vast majority of the most commonly used medications. 

On the other hand, there are some medications that may cause the opposite effect to xerostomia: hypersialia — also ptyalism or sialorrhea — that is, an excessively abundant production of saliva. It does not have the risks inherent in xerostomia but can cause discomfort for those who suffer from it. This group includes PSNS agonists such as pilocarpine, cevimeline, or bethanechol. 

• Chemotherapy and/or radiation therapy of the head and neck. In either case, these can produce damage and even destruction of the salivary gland tissues, causing atrophy. This results in xerostomia that may be reversible in the case of chemotherapy but is usually irreversible with radiation therapy. 

• Social and dietary habits. Consumption of substances such as tobacco, alcohol, caffeinated beverages, and spicy, salty, and acidic foods, as well as other habits such as mouth breathing or snoring, can cause dry mouth. 

Systemic factors 

Systemic factors include those pathologies or conditions not located in the oral region but that may have an impact on xerostomia: 

• Pregnancy. The fluctuation of hormone levels, oral pH and saliva composition inherent in pregnancy lead to an increased prevalence of xerostomia in expectant mothers. 

• Ageing. As people age, there may be a slight dysfunction of the salivary glands, which together with the fact that the elderly are often polymedicated, makes prevalence of xerostomia amongst this demographic very high. In addition, in the case of menopause, the decrease in sex hormones and changes in the biochemical composition of saliva cause xerostomia to be more pronounced. 

• Autoimmune diseases. The autoimmune disorder most commonly associated with xerostomia is Sjögren's syndrome, in which there is decreased secretion from the lacrimal and salivary glands. However, there are also others, including rheumatoid arthritis and systemic lupus erythematosus. 

• Endocrine disorders. Uncontrolled diabetes causes xerostomia due to increased urine output, parotid sialosis and alterations in saliva composition. Antidiabetic medication also causes xerostomia. Thyroid pathologies such as Graves’ disease, which is also an autoimmune disease, are likewise related to dry mouth. 

• Diseases of the nervous system. Stress, anxiety or depression may affect the nervous regulation of the salivary glands, decreasing their production. Furthermore, pharmaceutical treatment of these conditions exacerbates the disorder. • Certain infections, including bacterial (actinomycosis, tuberculosis) and viral (HIV, hepatitis C, cytomegalovirus, Epstein-Barr virus, etc.) infections, may infiltrate the salivary glands, hindering their ability to produce saliva. 

• Other pathologies or disorders, such as Parkinson’s disease, end-stage kidney disease, haemochromatosis, etc., are associated with increased risk of xerostomia. 

MAIN SIGNS AND SYMPTOMS OF XEROSTOMIA 

• Dry, irritated mouth 

• Halitosis 

• Burning sensation in the mouth and tongue 

• Difficulty chewing, swallowing, and speaking 

• Thick saliva (pasty mouth) 

The appearance of these symptoms significantly affects patients’ quality of life. In addition, the decrease in salivary flow increases the risk of numerous oral pathologies and disorders such as: 

• Caries, especially at the root 

• Fissured lips and tongue 

• Dental hypersensitivity 

• Burning mouth syndrome 

• Opportunistic pathogen infections; i.e. Candida spp. 

TREATMENT FOR XEROSTOMIA 

First of all, measures should be taken to improve moisturisation of the oral cavity. Drinking water frequently is therefore recommended to keep the mucosa moist. The use of humidifiers can help for severe xerostomia, especially at night, as well as using lip balms to moisten the lips. 

Avoiding irritating elements and foods, such as coffee, tobacco and alcohol, and spicy, acidic and/or salty foods is recommended, as well as encouraging consumption of fruits and vegetables. 

It is also essential for strict measures to be taken to maintain good oral health with two objectives: to moisten the oral cavity, and to prevent the appearance of disease: 

• Brush teeth three times a day for at least two minutes, with Tynex^® end-rounded filament brushes. 

• Use toothpastes and mouthwashes containing fluoride and moisturising ingredients, such as xylitol—which in addition to moisturising helps prevent caries at certain concentrations — or betaine, and without irritants such as sodium lauryl sulphate or alcohol, since these can exacerbate xerostomia. 

• Daily interproximal hygiene, either with dental floss/tape or with interproximal brushes. 

• Daily tongue cleaning with a tongue cleaner. 

• Regular check-ups by the dentist. 

Likewise, the causal factor of the xerostomia must be identified, and it must be determined whether this can be corrected. For example, if it is clearly associated with a medication, the doctor who prescribed it should be consulted to assess whether it can be replaced with another from the same therapeutic class and whose action is similar but without the potential to cause xerostomia. 

In severe cases where there is destruction of glandular tissue, artificial saliva or saliva substitutes may be useful. These are topically applied substances with a composition similar to saliva and whose objective is to moisten the oral cavity and increase the viscosity of saliva to relieve the feeling of xerostomia. The ingredients most commonly found in artificial saliva are carboxymethyl cellulose, mucin, hydroxyethyl cellulose, glycoproteins, and enzymes. Its main limitation is the short duration of relief—between 5 and 15 minutes—and in some cases it produces a strange sensation in the mouth. 

Finally, patients who show salivary gland activity can use topical and/or systemic sialogogues—substances that stimulate salivation. 

Systemic sialogogues are medications that significantly increase saliva production. The most widely used in Spain is pilocarpine. However, due to the numerous potential side-effects, it is mainly recommended for cases of severe xerostomia. 

On the other hand, topical sialogogues are active ingredients that can be applied locally in the form of spray, tablets or chewing gum and which stimulate the natural production of saliva. The best known and most effective are citric and malic acid. The latter has shown it provides a major improvement in salivation, with the advantage that it achieves the same salivary stimulation as citric acid but with a greatly reduced risk of causing dental erosion.