I need to have six crowns replaced on my top front teeth as soon as possible. I have some crowding on my bottom teeth. I would like to straighten the teeth first and I was wondering if Invisalign can be done while I have temporary crowns. I was told that when I come in to get the temps it would take two weeks to get the crowns. Can the time be extended? I have asked my cosmetic dentist and he said that the temps can fall off so he wouldn't recommend it.