The charcoal products, which are increasingly popular, often contain no fluoride to help protect the teeth.
And there is no scientific evidence to back up the claims they make, the authors say.
Excessive brushing with them can do more harm than good, they add.
They advise people to go to their dentist for advice on bleaching, or whitening, their teeth.
And they say it is better to stick to using a regular fluoride-based toothpaste.