Could your toothpaste actually be staining your teeth, rather than making them whiter?

That's the claim that was brought to KREM 2 reporter Rob Harris's attention, so he turned to local dentist Dr. Stephen Griffith with Grand Corner Dental to verify.

Dr. Griffith said yes, some toothpastes--notably, the Crest Pro-Health brand--contain stannous fluoride, which has been shown to cause teeth staining for some people.

"The stannous fluoride has been known in the past to cause internal staining," Griffith said. "It will oxidize the tooth and make it turn a more yellow color. But, Crest has since realized that and is trying to develop a toothpaste now with different additives that combat against that."

On its website, Crest says it uses stannous fluoride over the more commonly used sodium fluoride (which does not have the same potential staining properties) because it offers more protection to the tooth.

Crest also claims that the potential staining from stannous fluoride is neither harmful nor permanent. Dr. Griffith verified that this true.

"It is reversible," Griffith said. "Not with another type of whitening toothpaste, but with a bleaching agent. So, when people go to the dentist to get their teeth whitened, they're doing an internal whitening, so what that's doing is it's kind of reversing that yellowing and that oxidation."

For the record, Dr. Griffith said that many of his patients use Crest Pro-Health and do not see staining. Differences in teeth and saliva anatomy between people may explain why some react differently to certain toothpastes.