Saliva: What Is, Composition, Functions, and Secretion Disorders

What Is Saliva?

Saliva is 99% water and organic components (proteins and enzymes) and inorganic components (calcium, fluoride, phosphate, carbonate, sodium, potassium, chloride, and others). Additionally, saliva contains serous transudate, gingival crevice secretion (gingival fluid), nasal and throat secretions, desquamated epithelial cells, leukocytes (blood cells – white blood cells – responsible for the body’s immunity), microorganisms, and food residues.

Where Does It Come From?

Saliva is produced by salivary glands – 6 large and 200-400 small – located in different parts of the oral cavity. They are not present only in the gums and the anterior part of the palate. About 90% of saliva is produced by large salivary glands – the rest – small. There are 3 types of salivary glands depending on the type of saliva they grow; these are serous, mucous, and mixed glands.

The Paired Parotid Glands

Large salivary glands are paired, meaning they occur symmetrically on both sides of the human oral cavity. The largest glands producing saliva are the paired parotid glands. Their secretions enter the oral cavity through specialized ducts known as Stenon’s ducts, which open on the cheek mucosa in the region of the maxillary molars, sometimes around the upper “seven” or between the upper “six” and “seven”. The saliva produced by the parotid glands is watery, serous, and enzyme-rich.

The Submandibular Glands

The second pair of large salivary glands, the submandibular glands, have their duct openings (Wharton’s ducts) behind the lower “ones.” Their secretions mostly consist of a serous component but are generally mixed.

The Sublingual Glands

The excretory ducts (Bartholin’s) of the third pair of salivary glands, the sublingual glands, open next to the Wharton’s ducts. The saliva secreted by these glands is also mixed, with a predominance of mucous.

Composition

Saliva is 99.5% water, which is why its secretion is so dependent on the degree of hydration of our body. In addition, its composition is influenced by internal factors (including stimulation of receptors in the oral cavity, existing diseases, and physical activity) and external factors (e.g., time of day or season).

Its special properties are due to several key components:

• Lysozyme – is the main enzyme involved in oral cavity protection. The action of muramidase leads to the destruction of the cell walls of bacteria of the Neisseria and Streptococcus mutans genus
• Lactoferrin – inhibits the multiplication of bacteria by binding iron necessary for their proper metabolism
• Mucins – glycoproteins and one of the most important proteins in the oral cavity, which are responsible for the density of saliva (and therefore its protective functions and facilitating the swallowing of food bites) and binding caries-causing bacteria into large and easy-to-remove conglomerates
• Immunoglobulins – IgG, IgM, and in particular IgA (in the form of sIgA located on mucous membranes), which build an immune response to bacteria, viruses, and fungi
• Salivary amylase – a digestive enzyme whose role is the initial digestion of carbohydrates (among others, it is responsible for the digestion of 30% of consumed starch)
• Defensins – a group of small amino acid residues that have antibiotic potential by disrupting bacterial metabolism

In its remaining part, it also consists of:

• Inorganic ions (sodium, potassium, chlorine, calcium, carbonate ions)
• Carbohydrates
• Lipids
• Hormones
• Uric acid
• Urea
• Creatinine
• Growth factors and elements of the so-called mixed saliva–gingival fluid, serous transudate, white blood cells, desquamated epithelium, dead cells, bacterial residues, and secretions from the nose and throat

Functions

Saliva is crucial in maintaining oral health by benefiting soft tissues like the mucous membrane and hard tissues like teeth. It serves three primary functions: protective, related to food intake, and related to speech.

The protective function of saliva is achieved through various means. Firstly, saliva has antibacterial, antifungal, and antiviral effects because it contains special compounds such as lactoferrin and lysozyme. It affects bacteria’s settlement in the oral cavity, their metabolism, and growth. The presence of saliva reduces the amount of acids potentially produced by bacteria, the adverse effects of which I will explain later in the article.

Secondly, thanks to the content of water and other substances, saliva is a natural lubricant and is responsible for moisturizing, diluting, and removing substances entering the oral cavity. Accelerating the removal of food residues, especially sugars supplied with the diet is one of saliva’s most important functions. Using chewing gum after a meal stimulates the secretion of saliva, thanks to which food residues are removed faster.

Chewing gum can only be chewed until its taste is lost (about 5 minutes) because, after that time, it loses its properties. Longer chewing can cause adverse changes in the masticatory muscles and excessive abrasion of the teeth. It is also worth rinsing or brushing your mouth thoroughly after each meal.

Thirdly, saliva has an acid-buffering effect. This means that if any acidic compounds (such as carbonated drinks or bacterial metabolism products, i.e., food remains “processed” by bacteria) enter the oral cavity, saliva neutralizes them to some extent. This is important because, in an acidic oral environment, the incidence of caries increases.

A very significant example is florid caries (i.e., caries affecting all surfaces of the tooth, even those rarely affected by the carious process), which occurs, for example, in people after radiation of the head and neck area and in elderly people, in whom salivary secretion has decreased. Salivary secretion may decrease with age due to damage to the salivary glands resulting from cancer treatment with radiotherapy. Additionally, elderly patients often take numerous medications, some of which may hurt the amount of saliva secreted.

Fourthly, saliva affects the structure of the tooth enamel (the external tissue of the tooth, described in more detail in the article entitled The structure of teeth and periodontium). The enamel is constantly being rebuilt in demineralization (which can be explained as the continuous loss of ions from the tooth surface) and remineralization (this is the reverse process of demineralization and involves the incorporation of ions into the tooth surface). At one moment, remineralization predominates, and at another, demineralization predominates. The advantage of one process over the other depends on the pH of saliva (i.e., how acidic it is) and the concentration of calcium, phosphate, and fluoride ions contained in saliva.

Demineralization is a negative process, and if it is not properly balanced by remineralization, the structure of the enamel is damaged, which allows for the formation of caries. The high content of calcium, phosphate, and fluoride ions and the simultaneous elimination of an acidic environment (by brushing teeth, avoiding drinking sweetened beverages, chewing sugar-free gum, and the previously mentioned buffering effect of saliva) allows for the remineralization of the enamel structure, which protects the tooth from caries. A natural tooth contains calcium. However, fluoride toothpaste displaces calcium, and fluoride replaces it in the enamel.

Enamel rich in fluoride is more resistant to acid attack, and therefore, dentists encourage their patients to use fluoride toothpaste. Fluoride also affects tooth formation (when buds are still in the bone) and directly affects bacteria metabolism. Saliva’s second function involves its influence on food intake. It is responsible for preparing a bite for swallowing, partially digesting food, and allowing us to taste.

Lastly, saliva contributes to speech by moistening the oral cavity, emphasizing its importance for clear articulation.

Salivary Secretion Disorders

There are some salivary secretion disorders. We usually talk about drooling and dry mouth.

Drooling

Excessive salivary secretion (drooling) can be a perfectly physiological process. It occurs not only after stimulation by appropriate factors but also in pregnant women during the first trimester, which will also be accompanied by nausea and vomiting.

Physiological is also drooling in children (a large amount of frothy saliva) up to 3 months and in the case of small children who are teething. However, in many other cases, drooling will indicate a disorder or disease of the body. It is the case, for example, with vomiting large amounts of saliva (not food) in children, which may indicate obstruction of the digestive system at the esophagus. The most common cause will be mouth and throat infections (including more serious ones like diphtheria).

Sialorrhea will also occur in the case of:

• Retropharyngeal and peritonsillar abscess
• Motion sickness
• Wilson’s disease
• Poisoning
• Mononucleosis
• Neurological disorders (such as Parkinson’s disease or ALS)
• Malignant neuroleptic syndrome
• Chemical burns
• Medication use (especially antipsychotics)

Dry Mouth

However, dry mouth (xerostomia) is more dangerous in its effects. Due to the number of functions performed by saliva, its absence causes the accumulation of food residues and strong acid effects; thus, it increases the process of cariogenesis (enamel demineralization) and contributes to the formation of advanced caries and ulcers on the mucous membranes. Dry mouth is manifested by:

• A burning sensation in the mouth
• A feeling of a stiff and dry tongue
• Difficulty speaking
• Difficulty swallowing food
• Disorders of the sense of taste
• Ulcers of the mucous membranes
• Progressive tooth decay

Problems With Swallowing

In addition to problems with saliva secretion, problems with swallowing are also significant. Pain when swallowing saliva may indicate inflammation of the throat. Difficulty swallowing also accompanies inflammatory or neoplastic obstacles in the oral cavity, pharynx, and esophagus. Blockage of the ear during swallowing saliva is associated with a disruption of the patency of the auditory tube (Eustachian), ear infection, or ear blockage by wax or foreign bodies.

The Appearance And Smell

The appearance and smell of saliva are influenced by the homeostasis of our body and external factors and substances that we introduce into it.

Thick Saliva

Several saliva parameters have long been used in medicine as diagnostic indicators. One is density (normal results are in the range of 1.002–1.012 g/ml).

As mentioned above, it increases primarily with the increase in mucins found in it, sometimes also in connection with the increased content of other solid components. In many cases, thick saliva is considered one of the criteria for diagnosing specific diseases, among which we can mention such health problems as:

• Bacterial, viral, and fungal infections of the oral cavity
• Disorders of the functioning of certain salivary glands
• Diabetes
• Kidney dysfunction
• Cancer
• Acquired immune deficiency syndrome

Excessive Saliva

Another symptom of the disease is often excess saliva in the mouth. The direct cause of the so-called drooling is hyperactivity of the salivary glands or difficulties swallowing the secretion produced. The etiopathogenesis of these phenomena is diverse.

Larger amounts of saliva are produced at the sight or in response to the taste and smell of certain dishes (especially spicy and sour ones), which is a natural, physiological, and desirable state. However, if this symptom occurs in isolation from the consumption of food products and is constant, it should be a cause for concern.

Depending on other symptoms, excessive saliva production may indicate the following diseases and dysfunctions:

• Neurological disorders, such as Parkinson’s disease, amyotrophic lateral sclerosis
• Genetic diseases and disorders, including Down syndrome or Wilson’s disease
• Cancers of the oral cavity and esophagus, including cancer of the larynx or throat
• Mononucleosis is an acute infectious disease caused by the EBV (Epstein-Barr) virus
• Rabies, which occurs after being bitten by a wild or unvaccinated domestic animal
• Various types of bacterial, viral, and fungal infections stimulate the body to secrete saliva to use the antibodies and other elements of the immune response contained in them

Saliva Tests

If someone experiences saliva secretion disorders, their dentist might suggest saliva tests, especially if there’s a moderate or high risk of cavities. These tests evaluate saliva quantity, buffering capacity, and pH levels and can also detect cariogenic bacteria like Streptococcus mutans and Lactobacillus spp.

How To Reduce Ealiva Secretion?

To reduce saliva production you can:

• Treat the underlying disease that is the cause of drooling
• In the case of inflammation, use local anti-inflammatory preparations such as lozenges, sprays, or pharmacy rinses.
• Maintain thorough oral hygiene using a toothbrush, floss, and mouthwashes
• Avoid spicy and acidic foods that stimulate saliva secretion
• Drink or rinse your mouth with herbal mint infusion
• Chew gum

How To Increase Saliva Secretion?

Increasing saliva secretion methods include:

• Treat the underlying cause of xerostomia
• Hydrate intensively, an adult needs at least 2-2.5 l of fluids per day, and during periods of high temperatures or increased physical activity
• Limit your intake of caffeinated beverages and choose their caffeine-free substitutes
• Quit smoking
• Use humidifiers
• Rinse your mouth with non-alcoholic mouthwashes or sage solution
• Suck on sugar-free candies
• Use so-called “artificial saliva” in the form of over-the-counter sprays that mimic the moisturizing properties of natural saliva

Sources

• Physiology, Salivation. NIH.
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• Anatomy, Head and Neck, Salivary Glands. NIH.
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• Anatomy, Head and Neck, Parotid Gland. NIH.
  https://www.ncbi.nlm.nih.gov/books/NBK534225/
• Anatomy, Head and Neck, Submandibular Gland. NIH.
  https://www.ncbi.nlm.nih.gov/books/NBK542272/
• Anatomy, Head and Neck, Sublingual Gland. NIH.
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• Saliva composition and functions: a comprehensive review. NIH.
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• Salivary gland function, development, and regeneration. NIH.
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• Demineralization–remineralization dynamics in teeth and bone. NIH.
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  https://www.nidcr.nih.gov/health-info/dry-mouth
• Swallowing Disorders. NIH.
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• Managing excess saliva and drooling. NHS.
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• Dry mouth. NHS.
  https://www.nhs.uk/conditions/dry-mouth/