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Saliva is produced by three pairs of major salivary glands: the parotid, the submaxillary, and the sublingual saliva glands. Major salivary glands produce 0.7–1.0 L of saliva daily, especially during mealtime. This saliva has a fluid texture. These glands are relatively preserved in syndromes with dry mouth, at least at the beginning of the disease.
The mouth also contains approximately 500 minor salivary glands, located directly under the mucous membrane of the cheeks, lips, and soft palate. Their number decreases with aging. This saliva has a viscous texture, which largely contributes to the oral comfort between meals, in particular, when swallowing and speaking. The alteration of minor salivary glands is responsible for signs of discomfort and for the pain occurring in syndromes with dry mouth.
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Saliva constitutes 99% of water. It also contains positive ions (sodium, potassium, calcium, and magnesium), negative ions (chlorine, bicarbonate, phosphate, and thiocyanate), some urea, carbohydrates (citrate and lactate), lipids (cholesterol), and proteins (antibodies, enzymes, and mucins). Among proteins, antibodies and certain enzymes (lysozyme) contribute to the defense of the mouth against cariogenic bacteria and oral fungi (Candida); they stimulate the healing of mucous membranes. Other enzymes act in the first stages of the digestion, during food chewing (amylase, lipases). Mucins are the structural proteins of the saliva: they possess glucidic chains that fix water molecules just like sponges and ensure the hydration of oral mucous membranes.
There are also a large number of bacteria in saliva, which contribute to its texture. Both saliva glycoproteins and endogenous bacteria contribute to the viscoelastic and lubricating properties of the saliva.
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Saliva can be acidified by food, either directly if food is acid (fruits or sodas) or following the transformation of sugars in acids by the bacteria in dental plaque (candies or sweet drinks). Several salivary compounds (carbon dioxide/bicarbonate pair, phosphate, or urea) act as chemical buffers to neutralize acidity. Buffers have a key role, as acids solubilize tooth enamel and dentin, resulting in dental caries. Salivary calcium is important for remineralizing teeth attacked by acids. This is why the people with oral dryness, which reduces the capacity to neutralize acids and to recalcify teeth, have an increased risk of dental caries.
Saliva substitutes contain water and salivary ions. For example, they are commonly formulated with sodium chloride, potassium chloride, calcium chloride, magnesium chloride, dipotassium phosphate, and monopotassium phosphate. Some oral care products against oral dryness also contain milk or egg proteins (antibodies, lysozyme, etc.) or complex carbohydrates to fix water.
However, no artificial saliva can replace the entire components of the “native” saliva produced by salivary glands, and even less the “mature” saliva, which physiologically contains bacteria necessary for the hydration of oral mucous membranes.
Overall, saliva is a multifunctional fluid that protects teeth and oral mucous membranes, ensuring the first stages of food digestion and the comfort and the hydration of mucous membranes and allowing the movement of the tongue and lips during swallowing, chewing, and speaking.
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Saliva displays many functions, and it can be stimulated by multiple manners.
The ascending nervous ways lead external stimuli toward the brain. So, the view, the smell, and the noise produced by the preparation of food (e.g., the clatter of saucepans or flatware) can stimulate saliva secretion. In addition, mandible position and movements, as well as any contact on the oral mucous membranes, can stimulate saliva secretion (chewing a chewing gum or sucking a sweet). The sensation of hot, cold, pungent, astringent, salty, acid, bitter, sweet, aromas, and bubbles in beverages also stimulate saliva secretion via nervous pathways ranging from taste buds located on the tongue to brain receptors. Finally, pain in the mouth or visceral deep sensations such as hunger, thirst, and nausea can also stimulate saliva secretion.
At the brain level, memory and the simple thought of certain food can stimulate saliva secretion. However, salivation is a reflex: it cannot be voluntarily stimulated or inhibited by the thought. Exercise for increasing saliva secretion does not exist.
Either initiated by mouth receptors or memory stimulus, the command to secrete saliva comes from the brain, uses downward nervous ways and stimulates salivary secretory cells grouped into major and minor salivary glands, back to the mouth level. Pilocarpine is a molecule extracted from the leaves of a shrub Pilocarpus that is able to stimulate secretory cells (sweat, saliva, or tears). Anetholtrithione is another molecule present in dill, anise, and parsley, for instance, that can contract the excretory ducts of salivary glands and contribute to saliva secretion.
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In parallel with the evolution of Sjögren syndrome and other sicca syndromes of autoimmune origin, there is a progressive destruction of the salivary secretory cells. The cells that have been destroyed cannot be stimulated any more, and the treatment essentially relies on salivary substitutes and on the stimulation of the residual cells. It is the same treatment used when salivary cells are destroyed by radiotherapy in case of head and neck cancer.
However, oral dryness is a frequent drug-induced side effect. Many drugs can inhibit salivary secretion (atropinic drugs) without destroying the cells in which saliva is secreted. In this case, oral dryness is reversible, provided that the drug can be suppressed. Sometimes, it is possible to reduce the dosage or to substitute the drug by another one to improve the production of saliva. Actually, a risk of oral dryness can arise whenever a person takes 4–5 different drugs a day, whatever these molecules are. It is thus necessary to try to reduce the quantities of medicine to fight against oral dryness.
In older adults, a true autoimmune sicca syndrome and an oral dryness induced by atropinic drugs are frequently seen together. In such a case, the first-line treatment consists of the suppression or substitution of atropinic drugs.
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In the mouth, the saliva has two states, “liquid” and “solid.” The “liquid” state consists of the saliva that can be moved in the mouth with the tongue. The volume of residual saliva between two gulps is normally approximately 1 mL, but people with oral dryness have much less. There are also 105 bacteria/mL in suspension in saliva, which are invisible to the naked eye, but necessary for the optimal texture of saliva. This is why artificial saliva, consisting only of water and ions, does not bring the comfort of natural saliva. For that reason too, outside the mouth, saliva becomes very quickly malodorous. It constitutes a true handicap for people who drool, because they salivate too much (side effect of certain drugs) or they have swallowing alterations (caused by neurologic disorders or drugs such as benzodiazepines). It must be noted that there are no drugs that induce excessive salivation as a side effect that be recommended to fight against oral dryness.
The solid state of saliva is the oral microbial biofilm, which covers all the surfaces of the mouth. It is a complex assembly of bacteria, salivary components, human cells (mucous membrane and blood cells), food sugars, and acids. On teeth and dentures, the biofilm is called the dental plaque and contains 109 bacteria/g of dental plaque. The biofilm is very adhesive to its support and is not eliminated by tongue movements or by swallowing. It contributes to the sensation of comfort and hydration of oral surfaces and helps the movements of the mandible, lips, tongue, and uvula. A healthy biofilm is colonized by endogenous bacterial species, which are compatible with oral health as long as their growth is under control, these include Streptococcus salivarius. |
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In case of oral dryness, the biofilm is less hydrated and less elastic. It behaves as a semipermeable membrane and can be rehydrated only by its mucous side, by the saliva produced by minor salivary glands. The altered biofilm is not efficiently rehydrated by its external side. People with oral dryness have the feeling that the water drunk “slides in its surface” without rehydrating it. That is why to relieve oral dryness, it is recommended to keep a mouthful of water in the mouth for several minutes instead of drinking large quantities of water. It is one of the most effective small ways to relieve dry mouth. It can be practiced 5–10 times a day and avoids filling the bladder too quickly.
Furthermore, in case of oral dryness, the altered biofilm is often colonized by microscopic fungi (Candida species) and by other bacteria such as Fusobacterium species. The biofilm can then become visible to the naked eye, forming a whitish deposit on the surface of teeth, gums, tongue, and false teeth. In certain cases, Candida proliferates and the mucous membrane becomes painful: this is called an oral candidiasis. In frail elderly people, it is called the critical oral biofilm (COB), recalcitrant to nurse’s aides’ oral care.
Finally, the biofilm is very sensitive to the antimicrobial effect of antiseptic mouthwashes and certain drugs when they are crushed in food. This situation is frequent in case of swallowing disorders: tablets are crushed and capsules are opened, the drugs are mixed in food and put in direct contact with the oral biofilm. Paracetamol, for example, exhibits antibacterial properties in these conditions.
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Salivary disorders often cause a sensation of thirst, pain, mouth and lip dryness associated with ulcerations in the corner of lips (angular cheilitis) and intolerance to removable dentures. Patients can experience speaking and swallowing difficulties. There is a risk of choking, taste alterations, and malnutrition.
Besides, the people with salivary disorders are more often affected by oral infections (candidiasis, dental caries, and periodontitis). There is a risk of inhalation pneumonia related to swallowing alterations, and an increased risk of malnutrition related to edentulousness.
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Saliva: to avoid the inhibition saliva secretion, to stimulate saliva secretion, to replace saliva
To relieve oral dryness, it is necessary to avoid inhibiting saliva secretion by drugs. Some anxiolytic or antidepressant drugs, for instance, are often responsible for oral dryness. Furthermore, the risk of oral dryness increases as soon as a patient takes more than 4 or 5 medicines per day. Drug prescription must be reconsidered by the physician whenever possible.
It is possible to stimulate saliva secretion by eating diversified food: there is no dietary restriction but every patient is unique in his or her tolerance, choices, and food preferences. It may be helpful to also stimulate the olfaction, the view, and the hearing during meals (crispy texture). As long as it remains possible, the following list may be helpful to stimulate saliva secretion:
- to chew gum and to suck sugarless candies;
- to eat hot food or spicy food (pepper and hot pepper are authorized as long as they are supported);
- to drink fresh beverages and eat ice cream, suck small ice cubes, and have mentholated food;
- to chew food with solid texture such as raw vegetables and cooked vegetables and fruits (light acidity);
- to drink some sparkling water and sugarless sodas;
- to think of salting sometimes with a grain of cooking salt or to eat butter with crystals of salt; to drink and eat bitter products (tonic or bitter orange marmalade); and
- to favor products naturally rich in aromas (such as mature fruits and vegetables and cheeses).
Several drugs are also proposed to stimulate saliva secretion, such as pilocarpine, cevimeline, and anetholtrithione. Unfortunately, none of these drugs is safe and effective in all the patients, and currently, individual research of small means remains essential to relieve oral dryness.
Finally, to try to replace saliva, there are saliva substitutes in the form of sprays of electrolytes or ranges of gels, toothpastes, mouthwashes, and others, with more complex formulations. One of the most commonly used means is to keep a mouthful of water for a few minutes in mouth or to suck small ice cubes. The cost is nil and by spitting out the water without swallowing it, there is no unwanted effect (full bladder).
Oral biofilm: to avoid destabilization
To avoid destabilization of the oral biofilm, it is necessary to avoid antiseptic mouthwashes and antiplaque products, for instance those containing quaternary ammoniums compounds (chlorhexidine or hexetidine), triclosan, some alcohol, or antiseptic essential oil (rosemary, thyme, and eucalyptus). Sodium bicarbonate can also destabilize the oral bacterial biofilm.
Furthermore, the people with cognitive or neurologic disorders (swallowing troubles) have to crush medicine and mix them into the food. Crushed drugs are in direct contact with the oral biofilm and can inhibit some endogenous bacterial species. The resulting unbalanced biofilm can contribute to aggravate oral dryness.
An oily spray containing triacylglycerols (close to castor oil) is proposed in case of oral dryness. However, it so happens that the patients do not tolerate it over time.
Finally, dry mouth is often associated with lip dryness, with licking the lips with the tongue to hydrate them. This contributes to loss of saliva, which is already lesser than needed. To limit the loss of saliva, it is recommended to use officinal petroleum jelly on the lips.
Oral candidiasis: to disinfect removable dentures, avoid antiseptic mouthwashes, and eventually take antifungals
Short-term and long-term oral candidiasis is frequent at the people with oral dryness. Whenever possible, it is necessary to stop antiseptic mouthwashes. It is also necessary to disinfect removable dentures with brand products or highly diluted sodium hypochlorite (only for complete dentures without metallic pieces), and to not wear dentures, at least at night. Untreated decayed teeth and calculous constitute reservoirs of Candida cells. The treatment of oral candidiasis also relies on dental treatment and oral hygiene (new toothbrushes and toothbrush disinfection).
The treatment of oral candidiasis sometimes requires topical or oral antifungals prescribed by a physician or a dental surgeon. Angular cheilitis is characterized by cracks and ulcerations in the corner of the lips, which can be treated with a combination of two antimicrobials in cream formulation (fusidic acid and econazole). Other forms of candidiasis can require topical treatment in form of a drinkable suspension (fungizone or nystatin) or, in rare cases, via an oral route (fluconazole or itraconazole).
Oral hygiene and prevention of dental caries
It is necessary to respect the usual rules of oral hygiene to prevent and treat dental caries, but it is also important to consult a dental surgeon more often, at least twice a year. People with oral dryness particularly have to avoid sugar in candies and sodas, as well as snacking. Brushing teeth requires a manual or an electric toothbrush with soft bristles and fluorinated toothpaste. Patients with severe oral dryness, who do not tolerate mentholated toothpaste any more, can use menthol-free, fluorinated homeopathic toothpastes.
Hygiene of removable dentures
It is very important to clean removable dentures at least once a day and if possible after every meal. After the cleaning the dentures in the evening, it is recommended to remove them before sleeping to avoid the maceration of mucous membranes. In routine care, dentures must be cleaned with a specific denture brush or with a nailbrush reserved for this use and some toothpaste or household soap without coloring or perfume, which is very efficient and without danger. It is necessary to rinse dentures in tap water but never to let them soak in a glass of water, as there would be microbial growth in the water. At night, it is necessary to let the dentures dry, and in the morning to humidify them under water before putting them back. Effervescent tablets do not replace the manual brushing of dentures.
To prevent and fight protein–energy malnutrition
Oral dryness can lead to a loss of the pleasure to eat, decrease in appetite (anorexia), and loss of weight. The risk of malnutrition increases in case of stress, depression, disease, pain, or hospitalization. Conversely, malnutrition decreases muscle mass and immune defense, and it probably causes quantitative and qualitative changes in salivary proteins.
It is easier to prevent malnutrition than to treat it, and patients should not hesitate to speak about it with their physician, especially in case of recent involuntary weight loss. Furthermore, some insurance companies refund a consultation with a dietitian: this professional help should not to be neglected. In case of decrease of appetite or involuntary loss of weight, it is important to enrich protein and energy content of food under medical supervision. A physician or dietitian can recommend an enriched food (protein powder) or branded oral nutritional supplements (protein-rich milky creams and beverages or juices).
Overall, the main medical complications of oral dryness are pain with a psychologic and social echo, mouth diseases, malnutrition, and inhalation pneumonia in case of swallowing alterations. These complications add to all other symptoms of sicca syndromes.
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| Oral dryness is characterized by changes in the saliva and oral biofilm. There is no satisfactory treatment, but there are many options to try at the level of the food and oral hygiene. It is also necessary to identify and eliminate habits and drugs that can aggravate the situation.
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To avoid: Psychotropic drugs with atropinic properties
More than 4–5 drugs daily, with drugs being crushed into the food
Antiseptic mouthwashes
Wearing removable dentures at night
Soda, candies, and snacking
Oral hygiene: Toothbrush with soft bristles and fluorinated toothpaste (menthol free and homeopathic)
Dentures: Denture brush or nail brush and household soap (no coloring or perfume)
Food: To keep water or small ice cubes in the mouth, and then spit out the water
To suck sugarless candies or to chew mint gum
To eat varied food (no prohibition as long as it is not painful orally)
To chew food with solid textures
To enrich protein and energy content of food if needed
Medical treatments:
Pilocarpine, cevimeline, anetholtrithione, and a range of oral dryness products
Petroleum jelly on lips
Oral candidiasis: Antifungal treatment
Malnutrition: Oral nutritional supplements (protein-rich milky creams and beverages such as juices)
To consult a physician, a dental surgeon, and a dietician
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