A small mass of calcified tissue which forms in a salivary gland or one of the major salivary ducts. They may be asymptomatic but, when not, they are characterized by severe pain and glandular swelling due to the obstruction of the salivary flow. They occur most frequently in the submandibular salivary glands, possibly because of the viscosity of the secretion and the upward passage of the duct. Salivary stones can sometimes result in secondary infection. They may respond to massage or ultrasound (lithotripsy), but surgical removal may be necessary.