Xerostomia: Dry mouth. Xerostomia can be associated with systemic diseases, such as Sjogren's syndrome, systemic lupus erythematosus, and rheumatoid arthritis; and it can be a side effect of medication and poor dental hygiene. Xerostomia results from inadequate function of the salivary glands, such as the parotid glands. Treatment involves adequate intake of water, use of artificial saliva, and good dental care. Untreated, severe dry mouth can lead to increased levels of tooth decay and thrush.