Q: Asalam walaykum sheikh. Does wearing invisalign braces (which totally covers the teeth), impede purification? Do they need to be removed for every wudu/ghusl?
A: wa alaykum salaam. Great question. Swishing the water around in the mouth during wudu is of 2 levels. The obligation is to swish it around so that it comes in contact with a portion of the mouth. Mubalagha, which is sunnah, is to swish it around so that it comes in contact with all parts of the mouth.
I would suggest that the invisalign braces be removed whenever possible. If its possible to move the braces ever so slightly in the mouth top allow water to enter and come in contact with the teeth that would be sufficient to achieve mubalagha. Spitting out the water is not necessary to complete this step of wudu. If it becomes to cumbersome on the rare occassion to remove them, it should be fine to leave them in.
Sources: al-Mughni, Sharh al-Muntaha