I had mine done when I was a teenager, both upper and lower jaws.
Started out with metal braces on front, then onto plastic retainers when they were off. Finally, the upper jaw had a permanent retainer put in (posts glued to back of teeth and wire fitted).
However, my teeth began to shift slight in the upper jaw, meaning the permanent retaining wire began to slip out of the sides, which would gouge chunks from my cheeks, catch my tongue and cause ulcers etc. It was a constant battle having it redone.
Eventually, the teeth just began to overlap again, and the retainer gradually crumbled. There's about half of it left in there -- as in, the left side of upper jaw still has posts and wire, while the right has nothing (but crooked teeth).
Been like that for about 12 years now.