Impressions for Essix question

[gigiso]

Next week I go in and some of my back brackets will be removed. My ortho is going to at that appointment, put a bonded retainer on the lower teeth and do impressions for an Essix on the uppers. My question is how do they do impressions when there are still brackets on the front teeth?? Essix is supposed to arrive about 10 days later, at which time they'll de-bracket the front teeth.