What causes dry mouth?

Dry mouth increases your risk for the bacterial infection that causes cavities (caries)

Xerostomia, or dry mouth, affects millions of people and is not only a source of discomfort, but puts you at higher risk for developing cavities. It can be caused by a number of issues:

Naturally occurring: predisposed to having inadequate or sticky saliva
Medication induced: there are over 3,000 medications listing dry mouth as a side effect
Cancer treatment: radiation and chemotherapy
Genetic disorders: Sjogren's Syndrome, a relatively rare glandular disease
Mouth breathing

Regardless of the cause, a lack of saliva diminishes your body's natural ability to protect itself against cavities. Saliva provides natural cleaning of the teeth and has alkaline or buffering agents to neutralise the acids from foods or those produced by acidic bacteria. It has immune properties and starts the digestive process. The absence of saliva often leaves your mouth uncomfortable and your teeth more vulnerable to decay.

Use xylitol gum or alkaline saliva substitutes to stimulate your natural saliva production and to limit the acid production of bacteria. Use a 0.5% sodium fluoride rinse with xylitol and neutralising pH to help prevent a caries infection and remineralize teeth.
Limit not only sugary/carbohydrate containing items in your diet, but also even non-sugar containing acidic beverages (i.e. diet soda, coffee, tea, sparkling water, alcohol).

Drink plenty of water to help keep the mouth moist.
Practice regular brushing and flossing.
Reduce use of oral products containing alcohol or low pH.