It doesn't just give you a dry mouth. Sleeping with your mouth open would be just as harmful to your teeth as drinking soda.
Your saliva protects your mouth and teeth, but if you sleep with your mouth open, you have less saliva in your mouth. The pH levels in your mouth change, which can lead to tooth erosion and decay.
The pH value in your mouth is normally 7.7. Research shows that for those who sleep with their mouths open, the acidity drops to 6.6. In some cases, the acidity even dropped to a pH of 3.6, which is comparable to the acidity in your mouth when you drink fruit juice. Sleeping with your mouth open is an attack on your tooth enamel.
Did you know… 30 percent of men sleep with their mouths open, compared to only 5 percent of women.