Saliva is produced in response to reflexes triggered by taste stimulation and movements of the jaw muscles, joints and pressure on the teeth due to chewing. Three pairs of major glands controlled by the autonomic nervous system (the parotid, the sublingual and the submandibular) are responsible for the majority of salivary production as well as minor glands distributed around the oral cavity.

In the mouth, saliva controls the environment of the teeth and provides the body’s own natural protection against tooth decay, as well as fulfilling a number of other important functions in the mouth:

Protects the oral and perio-oral tissues

• Protects teeth and soft tissue in the mouth
• Lubricates with mucins and glycoproteins
• Protects against infection
• Acts as an anti-microbial and cleanser by breaking down bacterial cell walls and inhibiting growth
• Contains bicarbonate, which acts as a buffer by neutralising acid production and controlling plaque pH
• enamel with calcium and phosphates to help repair the early stages of tooth decay

Facilitates eating and speech

• Helps prepare food for swallowing by enhancing chewing
• Improves digestion by breaking down food using enzymes
• Enhances taste
• Enables speech by lubricating motor functions

Oral clearance

• Cleanses by washing away food debris from the mouth and teeth

Dental caries is the result of an imbalance between demineralisation and remineralisation.

Saliva is ‘supersaturated’ with the ions which make up the mineral content of the teeth (calcium, phosphate and hydroxyl ions) when the pH is above a ‘critical’ value, about 5.5. Below this value, the saliva and plaque are unsaturated and the tooth dissolves. Above this value, the calcium and phosphate ions in saliva start to repair the damaged mineral crystals in the enamel – the process of .

Normally, in a healthy person, loss of mineral is balanced by the reparative mechanisms of saliva.

The solid crystals of the tooth mineral, called hydroxapatite, dissolve to release calcium, phosphate and hydroxyl ions, only if the latter are below saturation concentrations. Below the critical pH, the high concentration of hydrogen ions reacts with the hydroxyl ions to form water and with the phosphate ions to form HPO42- or H2PO4-. This lowers the saturation and the reaction moves to the right; ie demineralisation will be favoured. If above saturation, the reaction will tend to move to the left and any damaged crystals will be repaired by the acquisition of ions from solution.

• Plaque pH falls each time acids accumulate in the plaque due to bacterial acid production following the consumption of fermentable carbohydrates – mainly sugars – in foods and drinks. After eating and drinking, plaque bacteria in the mouth can ferment the sugars and starches found in many foods and drinks, to produce acid. Within five to ten minutes, the acid formed can cause the pH to drop to a level low enough for the minerals in the tooth’s enamel to be dissolved (demineralisation) causing initial lesions (white spots) which can lead to dental caries.
• The plaque pH rises when the acids are washed out and neutralised by saliva, which contains the important buffer, bicarbonate and helps stop demineralisation.The calcium and phosphate in saliva can then help to repair the damaged mineral crystals in the enamel (remineralisation). The pH also rises when the plaque bacteria either metabolise the acids, or produce alkali, such as ammonia, from nitrogenous compounds found in foods and saliva.

Saliva is the body’s own protection against tooth decay and stimulated saliva does this best.

An increased saliva flow actively reduces demineralisation and improves the rate of remineralisation. Stimulated saliva contains more calcium and bicarbonate, and has a higher pH than unstimulated saliva. This results in a higher degree of saturation, making it even more effective at remineralising the enamel crystals damaged by an acid attack and is therefore better at fighting tooth decay. A greater volume and flow rate of stimulated saliva also results in an increased abilty to clear the remains of food, sugars and acids from around the teeth.

A healthy adult produces around 500ml of saliva per day. For most of the day the unstimulated flow rate is low (about 0.2-0.4 ml/min), but saliva can be stimulated by masticatory or gustatory activity. Saliva can be stimulated by any food or drink, but the most practical way of stimulating saliva is by chewing ORBIT sugarfree gum.

• Chewing sugarfree gum, such as ORBIT, can increase the salivary flow rate by a factor of 10
• Chewing sugarfree gum for 20 minutes after eating and drinking increases bicarbonate in saliva and helps patients to neutralise plaque acid
• Saliva stimulated by chewing sugarfree gum after meals and snacks has been proven to help reduce tooth decay by up to 40%

When we eat, both the taste of food and the chewing action stimulates a greater flow of saliva than at rest - but usually at a cost in terms of increased calorie intake, ie sugar or fat. However, chewing sugarfree gum stimulates the production of saliva without these drawbacks. It is especially effective after the consumption of fermentable carbohydrates such as sugar and starch. Chewing sugarfree gum for 20 minutes after eating and drinking has been shown not only to prevent the usual fall in plaque pH but also to help remineralise damaged enamel, so helping to prevent caries developing.

A severe absence of saliva in the mouth (dry mouth/xerostomia) can cause:

• Increased tooth decay
• Difficulty in eating, especially dry foods
• Pain or uncomfortable swelling
• General mouth discomfort
• Poor taste
• Denture problems
• Mouth and salivary gland infections
• Mouth ulceration
• Speech difficulties

Reduction in the amount of saliva is most commonly caused as a side effect of medication, systemic disease or pathologic changes in the salivary glands. Patients seriously deficient in saliva with Sjögren’s syndrome, or suffering from the effects on irradiation for head and neck cancer will display many of the symptoms above.

Demineralisation simply means the reduction or removal of minerals from the tooth’s enamel. After meals and snacks, bacteria in plaque produce acids, which cause the pH in the mouth to fall. If the pH falls below the critical level of 5.5 the tooth enamel starts to dissolve or demineralise and small white lesions (white spots) may appear.

Remineralisation is the replacement of lost minerals in tooth enamel. Stimulated saliva contains a higher concentration of the same types of calcium, phosphate and hydroxyl ions that make up the mineral content of the teeth. Consequently, stimulated saliva is an effective medium for replacing the lost minerals in enamel and repairing the early stages of tooth decay.

Stimulation of salivary flow increases the bicarbonate concentration in saliva. Saliva, especially stimulated saliva, is very important in maintaining a neutral pH in plaque and in the oral cavity. Its ability to perform this function can mainly be attributed to bicarbonate and to a lesser extent to phosphate as well as other factors.

Bicarbonate acts as a buffer and tends to control the hydrogen ion concentration in a solution by absorbing hydrogen ions when acid is present. At high saliva flow rates, bicarbonate is an important buffer against acid produced by dental plaque. In unstimulated saliva, the level of bicarbonate ions is too low to be an effective buffer. Chewing sugarfree gum has been shown to be an effective way to increase saliva flow.