Brushing your teeth before bed may not be enough to keep them healthy, with dentistry researchers warning that breathing through the mouth while sleeping may increase the risk of tooth decay.
A University of Otago study has found that people who breathe through the mouth have higher acidity levels than those who breathe through the nose.
The study found that at times the levels for mouth breathers got so acidic that they passed the level where tooth enamel starts to break down.
Lead author Joanne Choi said mouth breathers, and those suffering from sleep apnoea, were at higher risk of getting tooth erosion.
Ms Choi, a PhD student, said the research was in line with with observations from dentists worldwide that patients with sleep or respiratory disorders have more tooth decay.
Researchers studied the oral pH levels of 10 healthy volunteers who alternated between sleeping with and without a nose clip that forced them to breathe through their mouths.
Their study, published in the Journal of Oral Rehabilitation, found the average pH during sleep with forced mouth breathing was a mildly acidic 6.6 compared to a neutral 7 when nose breathing.
At times the pH levels fell as low as 3.6 during forced mouth breathing during sleep, well below the critical threshold of 5.5 when enamel starts to demineralise, Ms Choi said.
"Our findings support the idea that mouth breathing may indeed be a causal factor for dental diseases such as enamel erosion and caries."