I started wearing Invisalign 2 months ago and I just noticed one of my teeth is loose. Is that normal?

It's normal for your teeth to be slightly loose during invisalign treatment.  Since the treatment is geared around moving your teeth, the bone is constantly building on one end and being broken down on the other.  If you feel your tooth/teeth are very loose, it's important to communicate with your dentist right away because there could be a different issue.  You should also know that in order for the treatment to work properly and for you to have the best results in the safest way, you should wear your trays about 22 hours a day!