Breathing should be through the nose. However with allergies and some conditions it can seem impossible. This can cause (especially in children) facial distortion and dryness.
All upper teeth should make contact with lower teeth when biting. However in an open-bite, the back teeth all make contact, but the front teeth do not.
In a normal swallow the tongue goes up to the roof of the mouth. However with tongue thrust, the tongue pushes forward
Can cause distortion of the pallate.