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Teeth-whitening agents may harm enamel protein in high concentrations: study

TORONTO — Bad news for those aiming for the brightest smile — according to a new Canadian study, certain teeth-whitening agents may be more dangerous than previously thought, able to damage not just the surface enamel, but all the way to the centre of the tooth.

A study led by researchers with the University of Toronto and published last month in Nature Scientific Reports looked at carbide peroxide tooth whitening treatments, and found that the recommended application of just 10 per cent carbide peroxide can reduce enamel protein content by up to 50 per cent.

This loss of enamel protein allows the carbide peroxide (CP) to penetrate deeper into the tooth, leading to an increase in the death of dental cells themselves — but lessening the percentage of CP in the product may lower the risk.

Treatments containing CP are some of the most common types of tooth-whitening agents used at home. Irritated gums and teeth sensitivity has been noted before as side-effects of teeth whitening, but the effect on the deep inside of the teeth isn’t fully understood, researchers said.

“We have always been interested in the effect of peroxide-based tooth whitening on the tooth structure and its link to sensitivity,” Laurent Bozec, an associate professor in U of T’s Faculty of Dentistry and lead author of the study, said in a press release. “Here, we wanted to further understand the impact on the enamel itself and deep inside the pulp.”

Teeth have layers — the enamel layer is the outside, followed by the dentin and then the central “pulp” section.

The study explained that CP breaks down into hydrogen peroxide and urea and the whitening effect is thought to be caused by the hydrogen peroxide breaking down larger molecules in the dentin into smaller molecules that have “lesser or non-absorbing optical properties.”

Bozec had studied the effect of hydrogen peroxide on teeth before in the context of root canals, and had found that it caused damage to collagen. This raised the question of how it could penetrate from the enamel into the pulp, and what exactly it was doing to the teeth along the way.

To study the effects of teeth-whitening agents, researchers exposed 30 teeth — which were in a lab setting, not anyone’s mouth — to different levels of CP for around two weeks, while 30 other teeth served as a control. To make the circumstances as close to a real mouth as possible, researchers kept the teeth in artificial saliva between treatments.

Microscopic imaging showed that dental cells themselves had changed in shape after whitening treatment, with a greater change visible the higher the CP percentage of the teeth whitening agent used.

The enamel protein was also cut down by the teeth whitening process, with researchers suggesting that oxidative degradation created by the CP was to blame. The enamel protein was even affected at a low CP concentration of just five per cent, experiencing a 50 per cent reduction in enamel protein at five per cent and 16 per cent CP.

However, at five per cent CP, there was much less cell damage itself deeper in the tooth, the study said, while higher percentages had a much bigger impact on the cells themselves.

Some of the teeth whitening treatments and products for sale online can contain up to 35 per cent CP. At this concentration, researchers found that if CP made it to the dental pulp layer, dental pulp cells did not survive.

Researchers found that teeth whitening agents with both a high concentration of CP and a long exposure time — treatments with 35 per cent CP applied for four hours — produced “intense oxidative stress on both [gum cells] and pulp cells, associated with a severe reduction in cell viability,” the study stated.

Researchers noted that their study has some limitations, including not studying cellular recovery to see if any occurred after treatments, and studying the teeth in a lab setting as opposed to inside a person’s mouth.

Recommendations around teeth whitening may need to shift, the study suggested, adding that shorter exposure time to a teeth whitening agent, as well as lower CP concentration, can still provide the colour change that consumers desire while causing less damage to their teeth.

“Many home tooth-whitening products have such a high concentration of peroxide gel – for example, 35 per cent – and yet, little is known about what it does to the inside of our teeth,” Bozec said.

“We believe this is the first study of its kind to show the toxic effects of using a tooth-whitening agent. Our hope is that people will opt for a lower concentration of peroxide if they decide to use a tooth-whitening product as they are so much less harmful to your teeth.”

Consumers often reach for higher percentages of CP because there is a more immediate whitening effect on the teeth. But according to this new study, going for a white smile overnight may be bad for your teeth in the long run.

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