There’s an old axiom, “you never miss the water till the well runs dry”. How true is that, especially for saliva! The fact is, a world without saliva is like living in a drought. Saliva is important for the preservation and maintenance of oral health, so it is necessary for clinicians to have a good knowledge base concerning the norm of salivary flow and function.
Sources of Saliva
Saliva is a clear, slightly alkaline, mucoserous exocrine secretion. It is a complex mixture of fluids with contributions from major salivary glands (parotid, submandibular and sublingual) and the minor or accessory glands. Additionally, it contains a high population of bacteria normally present in the mouth, desquamated epithelial cells and transient residues of food or drink following their ingestion.
Composition
Saliva is composed of 99.5% of water and 0.5% of solid substances, out of which 0.2% are inorganic substances and 0.3% are organic substances. However their concentration is characterised by a wide variation in different individuals.
Properties
- The pH of whole saliva is around 6.7-7.4 whereas that of parotid saliva is 6-7.8
- Volume - Mean daily salivary output is 500 ml-1500 ml
- 20% Parotid
- 60% Submandibular
- 5% Sublingual
- The normal daily production of saliva varies between 0.5 and 1.5 liters. The whole unstimulated saliva flow rate is approximately 0.3-0.4 ml / min. This rate decreases to 0.1 ml / min during sleep and increases to about 4, 0-5, 0 ml / min during eating, chewing and other stimulating activities. 4
- Increased flow rate of saliva causes increased concentration of proteins, sodium chloride and bicarbonate, whereas it causes decreased phosphate and magnesium.
Types of saliva
- Serous / watery
- Mucous / thick
- Mixed
Functions of Saliva
Digestion
- Salivary amylase initiates digestion of starch and proteolytctivity.
- Starch digestion in the mouth may be either beneficial in aiding starch clearance or detrimental in liberating maltose for fermentation by oral bacteria to form acid - overall effect on caries is still undecided.
Lubrication
- Aids speech, mastication, swallowing and for general oral health and comfort.
Dilution and clearance
- Effect of water content of saliva is the dilution of substances into the mouth and their subsequent removal by swallowing or spitting
- Clearance is more rapid in some parts of the mouth than others. Unstimulated saliva is present as a thin film covering the hard and soft tissues of the mouth and the velocity with which this film moves over the surface determines the rate of clearance of a substance from different sites, rapid clearance, eg, lower anteriors and upper posterior teeth
- Clearance also depends on the type of saliva. More serous the saliva, higher the rate of clearance
Neutralisation and buffering
- Saliva is alkaline and is an effective buffer system. It reduces the drop in plaque pH reducing cariogenic potential of foods.
Bacterial competition
- Saliva plays a role in the control of the bacterial flora by acting as a selective growth medium. 1
Saturation
- Saliva is supersaturated with respect to tooth mineral which is responsible for growth of hydroxyapatite crystals during the remineralisation phase of the caries process.
- Inhibitors of precipitation - statherin and proline prevents the excessive calcification in the mouth, however they cannot penetrate the plaque due to large molecular size - unable to prevent seeding and calculus formation.
Techniques for Collection of Stimulated Whole Saliva
- Masticatory method (standardised piece of paraffin used)
- Gustatory method (1% - 6% citric acid used)
The spitting method for estimating resting flow and masticatory method with paraffin chewing for stimulating saliva for measuring flow rates are reliable.
Xerostomia
It is a subjective sensation of a dry mouth, frequently but not always associated with salivary gland hypofunction.
- Overall the most common cause of decreased salivary output is the intake of medications.
- A wide variety of medications referred to as Xerogenic drugs induce oral dryness
- Prevalence of xerostomia is not only related to drugs that are xerogenic but to the total number of drugs taken. As a general rule the drying and hyposalivatory effects of drugs are transient
- Anticholinergic, antidepressants, antihistamines, antipsycotic, antihypertensives, sedatives, diuretics and analgesics are all xerogenic
Diagnosis of Xerostomia
Clinically
Medical history, H/O radiation chemotherapy, oral infections, questionnaire.
Dentists should provide the patients with a dry mouth questionnaire -
- Do you sip liquids to aid the swallowing of foods?
- Does your mouth feel dry when eating?
- Do you have difficulties swallowing any foods?
- Does your mouth usually become dry when you speak?
Lab tests: flow rate tests, sialometry, etc.
Management
- Reassurance, symptomatic and supportive care.
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