So back in 2000 I got in a terrible car accident, but it changed my life in the sense that I got a set of 16 sexy porcelain veneers after the accident wrecked my teeth.

Today, I have had them for damn near 6 years and I don't feel that they look as good anymore. Specifically I find that they aren't as white anymore;

is this normal for them to be less impressive over time? Is there any way I can maybe brighten them up a bit? I have 4 years till I get my replacements so I want to know some things I can do to bring em back to life a bit!

Thanks in advance.