Salivary stones

A salivary stone or salivary calculus (also known medically as a sialolith) is a small calcified mass of saliva, which builds up in the excretory duct of a salivary gland and may cause the duct to become blocked.

If the saliva can no longer flow freely, the affected gland becomes painfully swollen.

Humans have three large salivary glands on each side of the face:

• the parotid gland
• the submandibular gland (also known as the submaxilliary gland)
• the sublingual gland below the tongue

Salivary stones occur most commonly in the salivary gland located below the jaw bone (the submandibular gland) and usually on one side only.

Measures to stimulate salivary flow often help to flush out the salivary stone. In some cases, stones have to be surgically removed.

Salivary stones are between 2 and 10 millimeters large, which is roughly the size of a pea. However, they may also grow to three times this size, especially in the submandibular gland.

Salivary stones may occur in several places within excretory ducts of the affected gland. They can sometimes even be seen within the oral cavity. They have a recognizable round or oval shape and are white to yellowish in color. Even if they cannot be seen, they can often be felt.

Smaller salivary stones frequently cause no symptoms. However, if a stone grows larger and becomes lodged in the excretory duct, it prevents the saliva from flowing freely out of the duct, causing it to accumulate and flow back into the gland. As a result, the salivary gland becomes swollen and may be painful. The symptoms typically occur when the individual is eating, as this is when saliva production is stimulated.

The swelling may be temporary before recurring after days or weeks or it may grow continuously. In general, only one side of the face is affected. If the pain intensifies and if patches of redness and a high temperature occur, these may be indications of inflammation and a bacterial infection.

The role of the salivary glands is to produce saliva, which is important for digestion. Saliva leaves the gland and enters the oral cavity through an excretory duct.

This duct may become narrower naturally or due to an inflammation or injury. This facilitates an accumulation of saliva, which in turn may lead to the formation of salivary stones.

The composition of the saliva also has a role to play. Saliva can be watery at some times and have a slimy/mucoid consistency at others, and it contains a wide range of minerals and proteins. It is not yet known what causes liquid saliva to form calcified stones.

Tiny calculi or bacteria are frequent triggers for salivary stones. If the flow of saliva is thick and slow, more and more layers become deposited in the duct and the stone increases in size. Finally, the stone will block the excretory duct and saliva will become blocked in the tissues of the salivary gland.

Salivary stones are particularly likely to occur in the submandibular glands below the floor of the mouth. This may be because these glands produce a thicker, more calciferous consistency of saliva than the other salivary glands. In addition, the excretory ducts from these glands are very long and the saliva has to be transported upwards against gravity. As a result, it flows more slowly.

Taking diuretic tablets or not drinking enough fluids can cause the body’s salt levels to drop below the required level.

This hinders the flow of saliva and increases the likelihood of salivary stones being formed.

There are also some types of medication that directly affect salivary flow and typically cause dry mouth.

In addition, certain health conditions increase the risk of salivary stone formation:

• narrowing or bulging of or injuries to the walls of the excretory ducts
• gout
• kidney stones
• chronic gum conditions
• smoking

Fewer than 1 percent of the population will develop a salivary stone that causes symptoms over the course of their life.

Men develop salivary stones more frequently than women, while children rarely do so. Most people who develop a salivary stone are between the ages of 30 and 60.

3 out of every 4 people who develop salivary stones develop a single stone. Salivary stones affect both sides of the face equally. It is rare for both sides to be affected at the same time.

When saliva becomes blocked in a salivary gland, the glandular tissue may become inflamed – especially in older people. In most cases, a salivary gland inflammation can be successfully treated with antibiotics. However, a large amount of pus may accumulate – this is known as an abscess.

If a salivary gland becomes chronically inflamed due to the blockage of saliva, the affect duct gland can lose its function so that saliva production is permanently decreased. If the cause of the blockage is eliminated in time, the salivary gland often recovers.

Doctors begin by examining the oral cavity and feeling the salivary glands and excretory ducts. An ultrasound scan is usually an effective way to identify and pinpoint the location of salivary stones.

During the examination, doctors sometimes administer a sour powder into the patient’s mouth to stimulate the salivary flow. A magnetic resonance imaging (MRI) scan or computed tomography (CT) scan may also be required.

Doctors can also use very narrow medical instruments to look directly into the excretory ducts. This procedure is known as a salivary duct endoscopy (sialoendoscopy). The benefit of this type of examination is that treatment can be administered at the same time.

Doctors can use a procedure known as salivary gland scintigraphy to check whether the salivary glands are functioning correctly. In this method, a radioactive substance is introduced into the bloodstream, which subsequently allows doctors to see the process of saliva production in action.

The most appropriate treatment option depends on the location and size of the salivary stone.

Salivary stones that are discovered by accident and are not causing any problems can initially be left untreated.

If the salivary stone is detected for the first time in a patient and is causing problems, the following treatment options are considered first:

• Substances that stimulate the saliva production, such as sour sweets or chewing gum, can serve to flush out salivary stones with the increased salivary flow.
• It is helpful to consider whether the patient is drinking sufficient fluids to facilitate the production of saliva.
• In addition, doctors can enlarge the opening of the excretory duct slightly and massage the salivary gland in the direction of the excretory duct to help loosen the stone.
• If there are signs of a bacterial infection of the salivary gland, antibiotics and anti-inflammatory painkillers are used to address this.

In many people, the symptoms will then recede.

If salivary stones continue to block the exit of an excretory duct, the following further treatment options are available:

• Using a very thin instrument called a micro-endoscope, doctors can locate a salivary stone directly and remove it. They sometimes also make a small incision during this procedure to extend the opening of the excretory duct.
• Shock waves are sometimes used to break salivary stones into small pieces by exposing them to short bursts of pressure waves. The shock waves can be delivered from outside the body or from within the excretory duct itself using an endoscope.
• Some people require surgery using an external incision or through the mouth. Doctors always try first to fully restore the salivary gland and the excretory duct. It is only in rare cases that the entire salivary gland has to be removed.