I had braces since I was in 4th grade until 7th grade. When I took my braces off in 7th grade, I wore my retainer for only about half of a year. I know I was supposed to wear it for a longer period, but I didn't. I am now in 10th grade and my teeth are still aligned perfectly (no retainer). Will they unalign someday because of the fact that I only wore my retainer for a short period?

You no doubt did not wear the retainer long enough to get the full benefit of all that work - but if you've gone 3 years and they're still perfect, then I'd not worry about it - but I would ask the orthodontist if he feels like making you a new retainer that will fit now is recommended.

Hi,
I agree with your previous answer, about checking with your Orthodontist.
Do you have any missing teeth? If so, your teeth will gradually shift into that particular place, becoming misaligned.
If not, then please talk with your Orthodontist, get his/her opinion. Best of luck.

I would like to know: How much do retainers cost?

About 250.00

Do as was mentioned, talk to your ortho and keep regular checkups.

I had braces and didn't wear the retainers nearly enough. Over time my lower teeth shifted some. Not terribly, but enough to wish I had worn the retainer more and kept regular checkups.