Xerostomia, or chronic dry mouth, is a medical condition that can pose problems for your mouth as a whole, and your tooth enamel specifically. Saliva contains minerals such as calcium and phosphate, which maintain and protect your teeth's enamel, but whenever you have a dry mouth, your spit levels are low (hence the "dry" in dry mouth). Therefore, when your mouth has less saliva, your enamel and teeth are more vulnerable than when you have a normal mouthful of spit [source: ADA].
But regardless if you have xerostomia, your mouth is naturally dry or you're on medication that causes the condition, there is hope. All you need to do to increase your mouth's production of saliva is chew. Chew your food more thoroughly while eating and lightly snack or chew gum between meals. If you want to really increase the amount of spit in your mouth, munch on a chewy food that you really enjoy. Taste and consistency play a large role in the amount of spit your mouth produces [source: ADA].