It sounds harmless, but dry mouth can contribute to tooth decay and gum disease. Many common medications such as blood pressure medication, antidepressants, incontinence medication and painkillers can dry out your mouth. So can treatments such as chemotherapy or radiotherapy to the head and neck. Dry mouth occurs when the saliva-producing glands in the mouth do not function properly. Your saliva helps defend your mouth against periodontal disease and tooth decay. It reduces bacterial levels in the mouth and contains minerals that help renew the surface of the teeth. Saliva contains enzymes and minerals that keep teeth strong and play a crucial role in maintaining a healthy environment in the mouth. Without sufficient saliva secretion, tooth decay and gum disease are more likely to occur.