I am on my 3rd tray now, of the invisalign express (10 trays), and it doesnt hurt it just feel like pressure. I have a gap on my top two front teeth so I didnt need the full treatment. On my next consult I will get a bit of the sides of my top front teeth filed so they can have some space to move back since I also have a bit of an over bite. The treatment seems to be working because the trays feel very tight the firs day or two I wear them and by the third day I dont even feel them anymore, also when I eat I feel my bite a bit different. Updated on 26 Jan 2012: I had my the sides of my 4 top front teeth filed a tiny bit (the width of a floss strand)today,it didnt hurt but it did feel a bit uncomfortable (although it took no more than 2 minutes).Now my front teeth should have a bit of space to move in.