Retainer help??

[Farquarhorses]

Hi,
I got my braces off a month ago, and of course I got a retainer. I have a solid plastic uppper piece and a wire with plastic beyhind the teeth for the bottom. Over the past couple weeks, I've been noticing a buildup starting to accumulate on the outside of the top piece. I know my orthadontist said somthing about what to do when that happens, but I don't remember exactly what they said. How do you get that stuff off? Please help me!!
Farquarhorses

[actionhero]

You're supposed to brush your retainer everyday using a toothbrush and some toothpaste. Thats what my dentist told me when I got mine.