If the amalgam of the filling is mixed with oil of cloves to soothe the nerve, then this does not invalidate the fast, even if you notice the taste of cloves, because nothing leaches out of the filling, or it is a very small amount that mixes with the saliva and cannot be expelled, so it is overlooked.

When the moulds used in teeth whitening kits are tightly placed over the teeth and gums so that nothing comes out into the mouth, in this case these moulds do not affect the validity of the fast.

If you used to swallow these bits of skin when you were able to eject them, then your fast is not valid, and you must make up the days on which you did that.

If saliva reaches the lips, then the person swallows it unintentionally, such as if he licks his lips and the like unintentionally, there is no blame on him. Similarly, if it dries up, then he closes his lips, its traces disappear when it dries up, and there is nothing left that could cause one to break the fast at all, whether deliberately or by mistake. If you deliberately swallow this saliva after it reaches the lips, then there is a difference of scholarly opinion as to whether that breaks the fast. For more details, please see the long answer.

There is nothing wrong with testing for sensitivity by injecting a saline solution under the skin, because this does not serve to provide nutrients.

There is nothing wrong with having a test or swab for Covid-19 during the day in Ramadan, whether the swab is taken from the mouth or the nose, because insertion of the instrument into the throat or nose does not break the fast.