This is why I did Invisalign... I had regular braces as a kid for like 4 years. After that and 4 extractions (I have a teeny mouth), my bottom teeth still went back to their original position. One tooth was totally behind another.
I wore the Invisalign for about a year and nine months. The good thing was with them is that I just didn't wear the aligners when I was riding and drinking anything sugary (water is OK). The few hours I had them out didn't seem to affect the course of treatment. It's been 3 years and I still wear my retainer aligners when I go to sleep. I was told that I could wean off of them, but any time I do, I notice my teeth start moving back to the original position. Very slight, but I notice it. Basically, the dentist told me that this always happens, no matter what kind of braces you have and you pretty much have to wear a retainer a few hours a day forever.
Whe i saw my son last weekend, I saw that despite his braces at ages 10-13, his bottom teeth are totally out of line and basically look like mine did before the Invisalign.