Ruling on Finding the Taste of Dental Floss in Mouth After Fajr
Question

I used mint-flavored dental floss after the pre-dawn meal, and the mint flavor remained in my mouth. I swallowed my saliva after dawn, and the mint flavor was present, so does this invalidate my fasting?
Praise be to Allah.The basic principle concerning flavoured dental floss is that saliva dissolves it and removes it from the mouth due to its small amount and the continuous flow of saliva in the mouth, and it does not have a substance that remains in the mouth. Therefore, if a Muslim uses it before dawn, the remaining flavor does not harm him, similar to the case of strong-tasting foods, like coffee and the like, where the taste remains after brushing and rinsing. This does not affect fasting due to the difficulty of avoiding it, and what is difficult to avoid does not break the fast even if it has substance.
Ibn Qudamah (may Allah have mercy on him) said:
"Whoever wakes up with food between his teeth is not free from two situations; one of them is that it is so little that he cannot spit it out, so he swallows it, and it does not break his fast; because it is not possible to avoid it, so it is like saliva. Ibn Al-Mundhir said: The Jurists have reached a consensus on this..." End quote from "Al-Mughni" by Ibn Qudamah (4/360).
The Hadiths, in their generality, indicate that the Prophet (peace and blessings be upon him) used to use the miswak while fasting, and this indicates that the remaining taste of the miswak in the mouth of the fasting person is not a problem and does not affect his fast.
For further benefit, please see the answer to question number: (108014 ), and number: (405051 ).
And Allah knows best.