A new study has suggested that sleeping with the mouth open can be as damaging to teeth as sipping a fizzy drink before bed.
New Zealand's scientists say breathing through the mouth removes the protective effect of saliva, which has a natural ability to kill the bacteria in the mouth that produce acid.
As acid levels rise through the night, tooth erosion and decay can begin. Tooth decay in mouth sleepers is often worse at the back, because the back of the mouth tends to get drier than the front.
Medics say patients with asthma are more likely to breathe through the mouth at night.