Here’s an article from www.livestrong.com on mouth breathing vs. nose breathing.
Effects of Mouth Breathing
According to the Academy of General Dentistry, or AGD, mouth breathing is often a problem for allergy sufferers, who experience airway obstruction during allergy season and are unable to breathe through their noses. Mouth breathing can lead to poor oxygen concentration in the bloodstream, which can lead to more serious medical problems such as high blood pressure, heart problems, sleep apnea and other sleeping problems.
DANGERS OF MOUTH BREATHING IN CHILDREN
Mouth breathing can be especially detrimental in children, who may suffer abnormal facial and dental development as a result. Left untreated, mouth breathing may lead to narrow faces, crooked teeth or gummy smiles. The AGD also reports that children who breathe through their mouths typically have sleeping problems, which can lead to poor academic performance and is often misdiagnosed as attention deficit hyperactivity disorder, or ADHD. In a 2009 study performed at the Federal University of Minas Gerais in Brazil, mouth breathers experienced higher rates of poor bite and misalignment of teeth.