Salivary gland stones are calcified deposits that can form within the salivary glands or their ducts, potentially obstructing saliva flow. This article explains the common factors and physiological processes that lead to their development.
What Are Salivary Gland Stones?
Salivary gland stones are medically termed sialoliths or salivary calculi. These are hardened mineral deposits that develop within the salivary glands or their ducts. They primarily consist of inorganic materials such as calcium phosphate, often in the form of hydroxyapatite, and sometimes calcium carbonate. Organic components like cellular debris, glycoproteins, and mucopolysaccharides are also part of their structure.
Most commonly, these stones form in the submandibular glands, located beneath the jaw, accounting for about 80% to 90% of cases. Less frequently, they appear in the parotid glands, situated in front of the ears, or rarely in the sublingual glands under the tongue or minor salivary glands. Salivary stones are typically white and hard, varying in size from less than 1 millimeter to several centimeters, though most are smaller than 10 millimeters. Stones smaller than 2-3 millimeters can be difficult to detect with some imaging methods.
The Formation Process of Salivary Stones
The development of salivary stones begins when saliva becomes supersaturated with mineral salts, particularly calcium and phosphate. Saliva naturally contains these dissolved minerals, but under certain conditions, their concentration can increase beyond their solubility limits.
Once supersaturation occurs, a microscopic nucleus or nidus forms, providing a foundation for stone growth. This initial core can be composed of various organic materials, including desquamated epithelial cells, bacterial debris, foreign bodies, or thickened mucus and mucin plugs. These small organic structures act as a scaffold, attracting the supersaturated calcium and phosphate ions.
Following the formation of this nucleus, there is a gradual and continuous deposition of mineral salts around it. Calcium and phosphate ions precipitate out of the supersaturated saliva and accumulate in concentric layers, causing the stone to grow in size over time.
Reduced salivary flow, a condition known as salivary stasis, significantly contributes to this process by allowing more time for mineral precipitation. When saliva moves slowly or is stagnant, the dissolved minerals have a greater opportunity to settle out of solution and deposit onto the forming stone.
Key Factors Contributing to Stone Development
Several factors can predispose individuals to the development of salivary gland stones by altering saliva composition or flow.
One significant contributor is dehydration, which leads to a decrease in overall fluid intake and subsequently, reduced saliva production. When the body is dehydrated, saliva becomes thicker and more concentrated, increasing the supersaturation of calcium and phosphate salts. This higher concentration makes mineral precipitation more likely, facilitating stone formation.
Certain medications can also diminish salivary flow, thereby increasing the risk of stone development. Drugs such as antihistamines, diuretics, and antidepressants are known to cause dry mouth as a side effect. This reduction in saliva volume and flow promotes salivary stasis, allowing minerals more time to settle and accumulate into stones.
Autoimmune diseases, such as Sjögren’s syndrome, directly impair salivary gland function, leading to chronic dry mouth and a heightened susceptibility to stone formation.
Inflammation or infection of the salivary glands, known as sialadenitis, or the ducts themselves, can create an environment conducive to stone development. Inflammation can alter the normal composition of saliva and increase the presence of cellular debris, which can serve as a nucleus for stone formation. The swelling associated with inflammation can also impede saliva flow, contributing to stasis and further mineral deposition.
Anatomical variations within the salivary duct system can also play a role. Narrow or tortuous salivary ducts can naturally impede the smooth flow of saliva, leading to areas of stasis where minerals can accumulate more easily. Trauma to the mouth or salivary glands might result in scarring or narrowing of the ducts, similarly obstructing saliva flow and increasing the likelihood of stone formation.
While not primary causes, some theories suggest that dietary factors may indirectly contribute to stone development. For instance, poor hydration linked to certain dietary habits can exacerbate dehydration. Smoking and alcohol consumption are also considered possible irritants that might lead to inflammation or changes in saliva composition, potentially influencing stone formation.