A new study at the University of Otago, New Zealand has shown that sleeping with mouth open increases the risk of dental decay or caries. This is because the mouth is dry when you breathe through the mouth while sleeping; saliva reduces the acidity in the mouth, thus when there is less saliva as in dry mouth, acidity increases.
High acid level affects teeth in two ways; it erodes the enamel (white of the teeth) and bores a hole in the tooth (tooth decay or caries).
Ten volunteers participated in the study for four days; sleeping with the open mouth to breathe for two days and with the mouth closed for two days. To ensure they breathe through the mouth for the two nights, they wore nose clips.
The result showed that the mouth of those who slept with open mouth had more acid than those whose mouths were closed.