The whitening toothpaste that can make teeth darker

So Katy Hill seemed the obvious choice to front a TV advert for a toothpaste that claimed it could deliver a glossy smile just like hers – with teeth up to three shades whiter.

But the advert has been banned after it emerged that 43 per cent of those who used Arm & Hammer Advanced Whitening toothpaste said their teeth looked the same – or even darker.

The toothpaste contains baking soda, which cleans, buffs and whitens teeth, according to the 150-year-old brand.

A clinical study by the manufacturer found that 39 per cent of users ended up with teeth that were up to three shades whiter. But the same research found that 25 per cent of participants in the fourweek trial were left with darker teeth – by up to 5.5 shades – while 18 per cent saw no change. The truth emerged following an investigation by the Advertising Standards Authority, which criticised the accuracy of the study and ruled the advert was misleading.

The ASA concluded: ‘Because the study was not sufficiently robust, and a significant proportion of subjects had darker teeth or no change after using the toothpaste, we concluded the whitening claims had not been substantiated.’

It said the TV commercial and similar marketing claims on the company’s website should be banned.

Church & Dwight, the US company behind Arm & Hammer, said it plans to run a new study to support its claims and allow it to run the Hill adverts in future.

Gleaming: Katy Hill fronts the TV advert which has been banned SHE is known for her shiny, bright smile, which she often flashed as a chirpy Blue Peter presenter.