Saliva

Saliva is like a bloodstream to the mouth. As does blood, saliva helps build and maintain the health of the soft and hard tissues. Saliva removes waste products and provides disease-fighting substances throughout the mouth, offering first line protection against microbial invasion or overgrowth that might lead to disease. The chemical nature of saliva has evolved in humans along with the oral flora and the teeth. Saliva is derived from blood and, as such, can be used diagnostically to detect disease.

Salivary Flow

Chewing is the most efficient way to stimulate salivary flow by causing muscles to compress the salivary glands and release saliva. Through internal feedback mechanisms the taste and consistency of food also affect the quantity of saliva produced. It is difficult to exhaust the salivary glands, so chewing throughout the day to maintain stimulated salivary flow is possible.

When salivary flow is reduced oral health deteriorates. Patients with dry mouths (xerostomia) experience difficulty chewing, speaking and swallowing. There are more than 400 commonly used Rx drugs that lead to mouth dryness. Common examples are analgesics, antihistamines, anti-hypertensives, anti-depressants, anti-anxiety agents, diuretics and appetite suppressants. Radiation, chemotherapy and autoimmune diseases also reduce salivary flow.

Saliva stimulated by chewing has a greater buffering capacity, providing more relief for gastric reflux. Saliva plays a significant role in maintaining oral health.

Saliva and the Plaque Biofilm

Plaque grows naturally on the teeth in the form of a microbial community called a biofilm. Saliva plays an important role in the development of the acquired pellicle, a protein film that forms quickly on a clean enamel surface. Microbes form their initial attachment to the tooth using the salivary pellicle film. Once attached the microbes then begin a new biofilm community.
Microbes live and thrive in the biofilm. Salivary flow brings biofilms nutrition, removes their waste and guards against metabolic changes that could disrupt oral homeostasis and manifest as disease. Since salivary flow throughout the mouth is innately uneven biofilms tend to become more disruptive in locations where salivary flow is slow.

The Minerals in Saliva

Saliva contains the minerals that maintain the integrity of the enamel surface and thus is the major caries preventive agent. Saliva enhances enamel protection by providing high levels of calcium and phosphate ions at the tooth surface. The initial film layer of plaque, the pellicle laid down by saliva, also acts as a selective membrane that controls mineral transfer between saliva and the enamel surface.

As enamel ages it becomes harder. On the enamel surface there is a constant cycle of mineral change.
The longer enamel is exposed to this saliva-mediated natural process, the more resistant it becomes to decay. After 20 years the enamel has been remineralized and the organic material it initially contained is lost. This may explain why the majority of new carious lesions occur in children and adolescents.

Alterations in Salivary Flow

Soft and hard tissues are healthiest where saliva flows freely. When we eat bread or other starchy foods the carbohydrates they contain do not easily dissolve in the saliva and block natural salivary flow. To ensure its free flow to all parts of the mouth, saliva contains amylase, an enzyme that breaks down starch into sugars that clear the mouth and re-establish a path for salivary flow.
Dry mouth, or xerostomia, is a chronic reduction in salivary flow. It can lead to altered taste, difficulty in chewing/swallowing and rampant tooth decay. Without saliva flowing the tissues in the mouth suffer, much in the same way body tissues suffer if blood circulation is disrupted.

Prescription and non-prescription drugs often cause reduction in salivary flow. Almost eighty percent of the most commonly prescribed medications lead to a dry mouth. Following radiation and chemotherapy the function of the salivary glands is often lost. Some systemic conditions, such as Sjogren’s syndrome, also compromise salivary flow.

Treating Dry Mouth

In addition to chewing sugar free gum, commercial products such as artificial saliva and tissue lubricants are also used to relieve dry mouth symptoms. If dry mouth symptoms persist, see your physician to rule out a possible underlying medical condition.

Protecting the Teeth
The Fluoride Reservoir

Only micro-quantities of fluoride are needed to have an impact on the re- and demineralization process occurring at the enamel surface. Immediately after brushing with a fluoride toothpaste, the fluoride level in saliva increases. Fluoride ions bond easily with calcium ions always present on tooth surfaces and in saliva.  Following a topical fluoride application, a “reservoir” of calcium/fluoride-like precipitates forms throughout the mouth. These precipitates are stored in the plaque and on the enamel surface. The sum of the precipitates is viewed as the “fluoride reservoir.” When plaque acid occurs, the calcium/fluoride-like material in the reservoir dissolves before the enamel, releasing fluoride exactly when and precisely where it is needed.

Saliva

Saliva is the mouth’s primary defense against tooth decay. Research has proven that fluoride works to prevent tooth decay by boosting the ability of saliva to return lost minerals to tooth enamel before cavities can develop. Saliva enhances protection of enamel by providing high levels of calcium and phosphate ions at the tooth surface. The presence of those ions slows demineralization and encourages an ongoing remineralization of tooth enamel. The best explanation of how fluoride works is that it enhances the natural remineralizing properties of saliva.

Saliva, Fluoride and Diet

Fermentable carbohydrates (cooked starches and sugars) present in the wide range of foods we eat also provide food for the bacteria that live in the plaque. Organic acid produced by the plaque biofilm as a by-product of its metabolism causes surface enamel to dissolve. Most times we eat there is a resulting acid attack on the enamel surface.  Interestingly, more sugar contained in a food does not generate more bacterial acid. Since even small amounts of sugars or starches will lead to similar acid conditions, making lists of foods that are “good” or “bad” for teeth is difficult. Today most advice is focused on trying to moderate the frequency of eating between meals while maintaining daily levels of fluoride.

Brushing twice daily with a fluoride toothpaste can help neutralize the effects of too frequent snacking by enhancing saliva’s ability to prevent or repair early tooth decay. Excessive snacking between meals leads to tooth decay. By snacking in moderation (three to four times daily), one limits the frequency of acid attacks and enables saliva enhanced by fluoride to sustain enamel integrity.
Chewing gum after a snack or meal stimulates salivary flow, clearing food from the mouth and neutralizing plaque acid. Gum chewing stimulates saliva production by up to 10 times the normal rate. Stimulating salivary flow changes the chemistry of the saliva. Stimulated saliva contains higher concentrations of bicarbonate, helping it to buffer plaque acid and fight tooth decay.

Reduced Salivary Flow

The importance of saliva is truly appreciated when salivary flow is reduced. Wherever salivary flow diminishes tooth decay and erosion are likely to occur. About 20 percent of adults occasionally experience reductions in salivary flow. Common symptoms include persistent dry mouth, pain, difficulty in chewing, tasting, speaking and swallowing. Problems with dentures increase when the mouth is constantly dry. Daily chewing programs can maintain salivary output throughout the day..