Praise be to Allah.
If the fasting person wakes up and finds any bits of food between his teeth, this does not affect his fast, but he has to spit out these bits and get rid of them, and that does not affect his fast unless he swallows them. If he deliberately swallows any bits that are left between his teeth, this invalidate his fast. But if he swallows them because he is not aware of the ruling or because he forgets, this does not affect his fast. But the Muslim should be keen to clean his mouth and teeth after eating, whether he is fasting or not, because cleanliness is required of the Muslim. End quote.