I stopped wearing mine before 2 years and my teeth really shifted and then it did not fit my mouth anymore. Go by your orthodontists recomendations you won't believe how fast the teeth shift after you stop wearing it for a while.
You do need to wear your retainer forever but ask your orthodontist how many hours a day he still wants you to wear it. Usually once the braces come off and they feel things are ok they will say to just wear it at night but everyone's ortho is different so get the exact instructions from your ortho doc.
My orthodontist had told me that I could eventually phase it out so that I wasn't wearing it at all. After quite some time of wearing it full time during the day, I started to only wear it at night. My teeth are just fine with that. But then he told me I could wear it every other night, and then try every third night, etc... and that is when I ran into problems. I tried every other night and it didn't work. My teeth began to shift and move. One of my front teeth actually started to move behind the other after just a few days of wearing it every other night. This was very recently. (I had braces when I was in elementary school and am now 22 years old and only now decided to start trying to wear it every other night.)
So anyway, I had to go get a new retainer made, and that one thankfully pushed my teeth back to where they were supposed to be.
I don't know about all of you, but my retainer is very comfortable. My orthdontist is one of the few that I know who doesn't use the wire retainers. He takes a mold of your mouth and then, much like the invisalign braces, makes a clear plastic tray that fits over your teeth. Once again, I am wearing it every night and I love it.
I think that if you have had braces, you have to wear the retainer every night because your teeth are not in their natural position and they will keep trying to move back. The retainer is what keeps them in place.
People ask me how I can continue to wear my retainer every night, 10 years after I got the braces removed. Even my orthodontist says that I am one of the only patients who has ever come back to get a second, third, and 4th retainer made (they get gross after a while, even with cleaning.) My reasoning is this: I wore braces for 4 years. If all I have to do to keep my teeth in position is wear a stupid little plastic retainer at night, why not do it?
I guess it depends on the person, but for me I think I will have to wear it forever.
The best thing to do is to ask your orthodontist for more exact instructions and estimations. I had braces for 2 years, and wore my retainer full time (day and night) for 2 years. By then I was starting my 2nd year of college. My orthodontist told me I could wear it just at night. I was pretty good about doing that until my 3rd year of college. That's when I started slipping. I told my ortho. that I was wearing every other night, but he seemed okay with it. My teeth shifted slightly if I didn't wear it for a few days, but they didn't look different. It was just more uncomfortable to wear my retainer when I put it back in. I'd say by my 4th year of college, I stopped wearing it completely which is when I stopped going to my ortho. as well. I never looked back, and my teeth still look straight and my overbite is fixed now at the age of 26.
So the moral of this story, follow your orthodontist's instructions. Don't do what I did even though I turned out okay.
When my sister (6 years younger than me) and I were in our prepubescent and early teens we had braces. After about 2 years I had stopped wearing my retainer and over 10-15 years or so later my teeth have not shifted to any noticable degree. My sister on the other hand stopped wearing hers and it looks like she never had braces to begin with.
For what braces cost (plus the time, pain in the butt of having to wear them, etc) I would highly recommend following the advice of other posters here and listen to your orthodontist.. though I took a chance and personally didn't have a problem or regret it.
I have had "the works" when it comes to dental stuff, and I have four younger siblings who all have had braces, retainers, and one even had to wear head gear (poor thing). I know this all from experience...
TEETH HAVE MEMORY!
You have to wear your retainer basically forever. Like someone else mentioned, some people's teeth will stay in one place, others really move. I've had my braces off for 6 years and I definitely still need my retainers. However, I have to switch between my bottom retainer and my mouth gaurd, and just in that one night of not wearing my retainer, my teeth move!
Try not wearing your retainer for a couple days and see what happens. If it's hard to get your retainer back on, then you'll clearly need to wear it more. You could keep doing this until you only need your retainer maybe one a month!?