Wow - so weird...
I was just on the AZ craigs list and someone posted this very question
Roxy has bad teeth. They stain very quickly, she has lost a few as well. Her last cleaning was with a Board Cert. Dental Vet. He said that when she was a tiny young pup she may have had a fever at the time of her enamel growth which causes _________ - I can't remember the whole thing, but I wonder if this is the same