Effect of Invisible Aligner on the Fast
Question

When fasting, do I have to take my invisalign out while making wudu? It can retain some water. If I have to take it off when making wudu, do I have to dry it from saliva before putting it back in my mouth, since when saliva exits the mouth it breaks the fast if swallowed again.
Praise be to Allah.After speaking with some orthodontic specialists, and direct observation of a person with clear aligners, and observing the removal and replacement of the aligners; it became apparent to us that the clear aligners retain a quantity of water during rinsing. It is also possible that water leaks  into the mouth without the person realizing it.
This remaining quantity exceeds the excused amount, which is what remains in the mouth after rinsing, estimated at between 1 to 1.5 ml at most through clinical medical trials.
(See: "Al-Mufattirat At-Tibbiyyah Al-Mu`sirah," Dr. Abdul Razzaq Al-Kindi, p. 172).
Therefore, since the user of the clear aligners can remove and install them alone without harm or difficulty: it is obligatory for them to remove them while fasting.  They can wear them from sunset to the Fajr prayer or they can remove them after each time they rinse their mouth and empty the remaining water in them.
And Allah knows best.