Black teeth

Question
A friend of mine has 2 pet rats that she is assuming are under 3 months of age. She acquired them from a pet store, and recently the top ''rodent teeth'' have black lines on the top of them where solid orange should be, two of her rats are affected by this and one of them has black spots instead of lines.  She is feeding them a mixed rodent food from a pet store in combination with a high quality dry food. I have quite a few rats so she came to me to help her with this situation but I have never experienced this before in any of my rats, and I cannot find any information online pertaining to anything of this nature. Any help you can give would be greatly appreciated.

Answer
Honestly, I have never heard of such a thing! I'd imagine it was from something they've eaten - was there anything that could leave a black residue on their teeth, bedding included? If you scrape at the spots, do they come off easily, or is it a pigment thing?

I'm so sorry, I wish I could help you more.