I would like an answer to the following question: is it permissible to use a finger-sized piece of sterilized cotton to wipe the tongue and teeth with, that is used to remove smells and germs and comes in various flavours such as mint, whilst fasting?.
There is nothing wrong with using what you mention, so long as none of it reaches the throat; rather you should spit out whatever of it is left in the mouth, or rinse out the mouth.
Shaykh Saalih al-Fawzaan (may Allah preserve him) was asked: In some pharmacies there is a kind of fragrance for the mouth, which is a type of spray. Is it permissible to use it during the day in Ramadan to remove odour from the mouth?
He replied: Instead of using the spray for the mouth when fasting, it is sufficient to use the siwaak which was encouraged by the Prophet (blessings and peace of Allah be upon him). If the spray is used and none of it reaches the throat, there is nothing wrong with it. But the smell that comes from the mouth of the fasting person as a result of fasting should not be disliked, because it is the effect of obedience and is beloved by Allah, may He be glorified and exalted. In the hadeeth it says: “The smell coming from the mouth of the fasting person is better before Allah than the fragrance of musk.”
End quote from al-Muntaqa min Fataawa al-Shaykh Saalih al-Fawzaan, 3/121.