What causes the parotid gland to spasm?

Parotid spasm: The parotid gland is on of the large glands that makes saliva. The duct or tube that drains it secretes saliva into the mouth from the cheek oposite the second molar. I that tube is blocked or partially blocked, the gland spasms as it tries to secrete the saliva. The tube can be swollen from an inflammatory process or there could be a stone, it could be from dehydration, or it could be from tumor.