Answered by Shaykh Faraz Rabbani
When a person swallows a small amount of food that was lodged in the teeth, after the fast starts-does it invalidates the fast?
Walaikum assalam,
If the food between the teeth was there before fajr time, and the amount swallowed was less than the extent of a small chickpea, the fast is not invalidated.
However, if it entered the mouth after fajr time, or if the amount swallowed was more than the extent of a small chickpea, then the fast is invalidated.
Wassalam,
Faraz