Both Invisalign and Braces move or change the position of the teeth. In order to do this, in may cases (especially extreme crowding) we need to make more space giving the teeth room to be guided into proper alignment. We call this "Slenderizing" or "Interproximal Reduction" (IPR). Teeth have a memory and are always in movement. Retainers prevent the teeth from shifting back into their former position.
There are a few options that can be discussed with your Dentist. Regular retainers are acrylic with some metal in them and eventually are worn only at night. Invisalign offers clear retainers. A fixed or permanent retainer can also be placed on the lingual (tongue side) of the teeth. It is a small thin wire that is bonded in place keeping the front/anterior teeth in place, for some patients this can work very well because it is bonded and always in place.
In my office I have before and after pictures of satisfied patients who are very happy with the resultsof Invisalign. (and other procedures) For the patients who want to do this we have them sign a release form that allows us to display their pictures and testimonials. Invisalign has a patient case portfolio on the website that can be viewed as well.