Salivary stones
Authors:   , Kraaij Saskia 
Published: August 2023

Salivary stones or sialoliths are calcifications that develop primarily in the drainage ducts of a salivary gland and less frequently in the gland itself. The submandibular salivary gland is most frequently affected (84%) and less often the parotid salivary gland (13%). Sialoliths occur incidentically in the sublingual salivary gland and accessory salivary glands.
The presence of a sialolith can lead to obstruction of the excretory duct. As a result, symptoms such as recurrent, mealtime-related swelling and pain of the affected salivary gland, may occur. The severity of symptoms can vary and is determined by the localization and size of the sialolith. The aetiology of sialoliths is unclear. Several hypotheses have been put forward that have attempted to explain the etiology and pathophysiology of sialolith formation.
The research described in this thesis mainly focused on submandibular sialoliths with special attention to possible factors that may be involved in sialolith formation, the radiological and clinical difference in size and volume of a sialolith and the composition of sialoliths.
Chapter 2 reviews the knowledge on the aetiology, symptoms, biochemical composition and treatment of salivary stones based on current scientific literature. Sialoloiths consist of an amorphous mineralized core surrounded by concentric laminated layers of organic and inorganic substances.
Successful removal of sialoliths depends on preoperative information about the exact location, size and shape of the stones. The accuracy of a preoperative CBCT-scan in determining the volume of a salivary stone has been examined in Chapter 3. This study showed that when CBCT-scans are used as a diagnostic tool, the sialoliths are actually a fraction smaller than determined by radiological examination. This is of clinical importance since cut-off values for stone size are used in choosing the type of treatment for stone removal.
Little is known about the relationship between lifestyle factors and the presence of sialoliths so it was examined in Chapter 4. This showed that patients with sialoliths used significantly more antibiotics than the control group. No association was found between the occurrence of sialoliths and systemic diseases such as hypertension, diabetes mellitus and rheumatoid arthritis. Smoking and alcohol consumption played no or only a limited role in the presence of sialoliths.
In Chapter 5, the inorganic composition of submandibular and parotid sialoliths was determined and the possible relationship between stone specific characteristics and patient-related characteristics investigated. Sialoliths were found to be composed primarily of inorganic material with carbonate apatite identified in 99% of stones, phosphate in 88%, calcium in 87%, magnesium in 68%, struvite in 44%, oxalate in 38% and carbonate in 35%. The biochemical, inorganic composition of submandibular and parotid sialoliths is related to size and consistency, probably to age, but not to patients gender.
Sialoliths consist, in addition to inorganic material, also of organic material. Proteins contribute about 5% of the dry-weight of submandibular sialoliths and they are mostly found in the core of the stone. Salivary proteins such as lactoferrin, lysozyme and s-IgA have the property of clumping together and reinforcing each other in their specific actions. Possibly, this clumping of proteins could play a role in the formation of salivary stones. Therefore, in Chapter 6, twenty submandibular sialoliths were examined for the presence of different salivary proteins. Using a combination of gel-electrophoresis and Western blotting, α-amylase was found to be present in all stones, lysozyme in 95%, lactoferrin in 85%, s-IgA in 75%, MUC7 in 60%, complement C4 in 60% and C-reactive protein in 35%. The presence of, lactoferrin, lysozyme, s-IgA and α-amylase in sialoliths was demonstrated by ELISA.
Future research may contribute to a better understanding of the pathogenesis of sialoliths.