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Saliva is often called the "body’s mirror"; there is great potential for salivary diagnostics for systemic and oral diseases. It is noninvasive, cost-effective, and painless for the patient. Saliva plays a pivotal role in the overall maintenance of a healthy homeostatic condition in the oral cavity, which from the dental perspective is usually considered to be related to protection of the teeth, periodontium tissues and mucosal surfaces. The oral cavity is also the starting point of the digestive system, so saliva has advantages in being easily accessible for sampling as well as providing an impact on systemic health. The complexity of this oral fluid is perhaps best appreciated by the consideration of its many and varied functions. The functions of saliva are largely protective; however, it also has other functions.
Our saliva is 99% water. The remaining 1%, however, contains numerous substances important for digestion, dental health and control of microbial growth in the mouth.
Micro-organisms and epithelial cells
Saliva, when secreted by the salivary glands, is sterile but whole saliva in the mouth may contain bacteria at levels up to 109/ml. For bacteria to survive in the mouth they must be able to attach to and proliferate on oral surfaces since the unstimulated salivary flow rate is too high for saliva to act as a continuous culture system.
Epithelial cells are continually being shed from the oral mucosa into saliva and it has been estimated that the surface cells stay attached for only about 3 hours before being desquamated. Each epithelial cell has about 100 bacteria attached to its surface and in saliva there are about three times as many bacteria bound to epithelial cells as are unattached. Most of the bacteria in saliva appear to be derived from mucosal tissues rather than from the teeth. However, after a prophylaxis, and in the subsequent absence of oral hygiene, the amount of plaque on the teeth will gradually increase until an equilibrium is reached when the rate at which bacteria are being shed from plaque into saliva is equal to the rate of their proliferation on the teeth. Thus salivary clearance plays an important role in removing bacteria and epithelial cells from the mouth and individuals with hyposalivation will have higher salivary bacterial and epithelial cell counts. In addition, salivary flow is very low during sleep (see Chapter 3), which explains why the salivary bacterial and epithelial cell counts are greatest before breakfast. Halitosis is thus usually most marked at this time of day since epithelial cells are one of the substrates from which some Gram negative anaerobes are able to form volatile sulphur compounds with an unpleasant odour.
Functions and properties of saliva
Saliva is essential for maintenance of the integrity of enamel:
+ By modulating demineralization, and remineralization.
+ Glycoproteins in the pellicle inhibit bacterial adhesion to the tooth surface, and reduce the erosive potential of cola drinks by up to 50%.
+ Saliva buffers acids by virtue of calcium, phosphate, bicarbonate, and urea to maintain the oral pH at 7.0 to 7.5.
Saliva contains epidermal, fibroblast and nerve growth factors for tissue repair. Gustin is necessary for growth and maturation of the taste buds.
Saliva is crucial for oral clearance: this can vary from 30 seconds in the mandibular anterior area, to 20 minutes around the maxillary anterior area. Certain drugs are excreted in the saliva.
Salivary amylase and lipase initiate digestion and mucin forms the food bolus for deglutition. Saliva is hypotonic to plasma in order to dilute food to the osmolality of plasma.
Swallowing saliva stimulates gastric secretions: recent studies by UK colorectal surgeon Alastair Windsor have found that patients recovered from bowel surgery sooner if they chewed gum.
Salivary peptides are antimicrobial, and secretory immunoglobulin ‘A’ neutralizes viruses and bacterial toxins.
Glycoproteins in mucinous saliva coat the oral surfaces to protect, lubricate, and facilitate speech, mastication, and swallowing. This also prevents esophageal damage.
Factors affecting salivary pH and buffering capacity:
+ Salivary flow.
+ Bacterial load.
+ Gastric reflux.
A low salivary flow rate increases acidity by impairing saliva’s buffering capacity, and increasing numbers of acidogenic bacteria, which are also aciduric — thriving in an acidic environment. If low salivary pH occurs despite a normal salivary flow rate and buffering, the possibility of GERD should be considered.
In conclusion, saliva is the key player in buffering the effects of acidic foods and beverages, and helps the body rebuild tooth enamel. Slowed salivary production leads to increase in cavity formation and weakened tooth structure.
The teeth and oral tissues are constantly bathed in saliva. Saliva is secreted by the salivary glands. The production of saliva increases when food or drinks are consumed. Its presence is vital to the maintenance of healthy oral tissue. Saliva has many functions including the following:
Functions of Saliva
Fluid/Lubricant: Coats mucosa and helps to protect against mechanical, thermal and chemical irritation. Assists smooth airflow, speech and swallowing.
Ion Reservoir: Holds ions needed for maintenance of enamel near the tooth. Helps prevent decay.
Buffer: Helps to neutralise plaque acids after eating, thus helps prevent decay.
Cleansing: Clears food and aids swallowing.
Oral Hygiene/ Antimicrobial actions: Helps control bacteria in the mouth.
Pellicle formation: Forms a protective coating on enamel.
Taste: Saliva acts as a solvent thus allowing interaction of foodstuff with taste buds to facilitate taste.
+ Saliva and oral health
an essential overview for the health professional
Michael Edgar, Colin Dawes & Denis O’Mullane
+ Fascinating facts about saliva
August 9, 2011
By Linda Douglas, RDH
+ Saliva between normal and pathological. Important factors in determining systemic and oral health
Gabriela Iorgulescu, J Med Life. 2009 Jul-Sep; 2(3): 303–307.