Answered by Mufti Mohammed Tosir Miah
Swallowing food stuck between the teeth whilst fasting
If a person swallows the traces of food that remains in between his teeth from the pre-dawn meat it does not break the fast provided it is less than the size of a chickpea. The reason the fast will not be nullified if the meat is less than a chickpea is that it is considered part of the saliva. If it is bigger than a chickpea, ones fast will break. (Maraqi Falah p.240)
The ruling is the same irrespective of whether the person is awake or asleep.
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham.