The other day in the drugstore at the checkout, I hear by chance that the customer complained to me just about the same phenomenon. After short discussion we are draufgekommen that we (ie this one) both use the same brush heads.
On closer inspection, I found that the back of the brush head so exposed a metal screw. I turned me to the Odol customer service.
There they knew the problem already evident. I was told that toothpaste with whitening substances can attack the steel gears in the brush head, thus small amounts of metal particles can get into the toothpaste. However, there was no health risk.
I taste the metal and even there is no health threat exists ?? In any case, it is disgusting! I looked so forced to renounce commercial toothpaste with Whiteningeffekt. That can surely not be. I think, as part of a warning on the packaging.
