One of my degus had a tooth that turned white. I thought she had a mouth illness, so I started putting a little less than a capful of this blue liquid marketed for cats and dogs to help prevent mouth infections in her water. Her tooth was back yellow again a week or so later. I don't know if it was the blue stuff that helped. I am not suggesting anyone try this, because it may not be safe. I only put a tiny bit. Also, when I noticed it, I gave her more veggies. That's probably what I did right. Good luck. Try not to freak out too much. But if you are worried, visit a vet. They'll know what to do.
Because I was born in the South, I'm a Southerner. If I had been born in the North, the West or the Central Plains, I would be just a human being.