Brenda,
I may have missed something so I'm going to ask you a couple of questions.
1. Have you had any radiation or chemo therapy treatment yet?
2. Do you see a dentist regularly and how often?
3. When did you first notice the teeth turning "black"? Did your dentist take x-rays since this occurred?
4. Is the bad taste sort of a metallic taste and does it seem to be coming from the darkened teeth?
5. Do any of the dark teeth have "root canals"?

If you can answer some of these questions I may be able to help you or steer you in the right direction for diagnosis and treatment.

Cheers,

Mike