Which condition is LEAST likely to cause Xerostomia?

Xerostomia, or dry mouth, is primarily caused by conditions that either directly affect the salivary glands or are associated with factors that inhibit saliva production. Among the options provided, a submandibular sialolith, which refers to a stone in the salivary gland, is the least likely to cause xerostomia in comparison to the other conditions listed.

When a sialolith is present, it may lead to localized swelling, pain, or discomfort, and can obstruct saliva flow; however, it does not inherently cause systemic dry mouth effects like the other conditions do. Conditions like Sjögren's syndrome are autoimmune diseases that specifically target and damage salivary glands, leading to persistent xerostomia. Emotional reactions can cause temporary dryness due to stress response, while many antidepressant drugs are known to have side effects that significantly decrease saliva production, contributing to xerostomia.

In contrast, while a sialolith can lead to temporary issues with saliva flow, it isn't a systemic condition and thus is less likely to result in the persistent dry mouth characteristic of the other options.