Praise be to Allah.
There is nothing wrong with using a retainer during the day in Ramadan, and what you mentioned about dry deposits, that do not dissolve in the mouth, does not affect that.
But these deposits should be cleaned off and removed whenever they form.
If it is difficult to remove them, they may be left as they are, and that does not affect the fast, as noted above.
For more, please see these answers: 1312 , 13619 , 82308 , and 13767 .
And Allah knows best.
Comment