How Does One Get Stones in the Salivary Gland?

QUESTION: I have never heard of this before, but that is of little importance
now that I have a case of stones in my salivary gland. Where do they come
from, and how do you treat this strange disease? Any information you can
offer would be immensely appreciated.
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ANSWER: Although stones in the gallbladder and kidney are better known,
stones in the salivary glands are not uncommon. Salivary stones (also called
sialoliths--"sialo" means "saliva" and "lith" means "stone") occur in about 1
percent of the population, especially in older individuals, and more often in
men than in women.
Stones can form in any of the saliva glands, but they usually occur in
the submandibular glands, the two located under the jaw with ducts that come
up just where the tip of your tongue rests. Stones usually form in this gland
because of its more viscous, alkaline saliva and higher calcium content. This
gland also has a longer curved duct that leads upward, which means its saliva
must flow against gravity.
A stone that forms or lodges in duct will cause swelling and pain.
Often, the stone can be removed by massaging along the salivary duct, but
sometimes it must be removed through relatively minor oral surgery.