Rotting teeth, gum disease, mouith soresk, "leftovers", and/or other diseases in the body. Poor oral hygience is supposed to lead to a lot of other health problems.
Sometimes it's the food people eat too, and no amount of brushing will really make it go away. I have a friend who went through a phase of heating whole cloves of raw garlic everyday, at least 3 or 4 of them. He was doing it for his health. He (his whole person) smelled of garlic so bad that you could tell if he had been in a room (apartment sized) half an hour before you. Luckily he finally quit. <img src="/images/graemlins/crazy.gif" alt="" />
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Paul