What are the attachments on the front lower teeth for with invisalign, to push back the teeth? In layman's terms please!

My orthodontist used band lock on my upper back molars, molars got shorter because of it! Then he cut the wires and had me rubber band all three back teeth for a month to get my teeth down so he could take the band lock off, so my teeth would not hit the bracket in the front teeth! Weird right? He screwed up the whole thing by doing this, I got spaces top and bottom/my right front teeth hit when I bite,then he took off braces! Now I have to have invisalign and my teeth were not bad first of all!

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