August 17, 2021 | Research

U of T researcher examines damaging effects of teeth-whitening products on dental cells

By Rachel Boutet

A woman smiles. Her teeth are very white.

(Photo by Elizaveta Starkova via Getty Images)

A study led by researchers at the University of Toronto highlights the extensive damage that can be caused by common tooth-whitening agents.  

Published recently in Nature Scientific Reports, the study assessed the dental cell damage caused by the use of carbamide peroxide teeth-whitening treatments. 

It found that a recommended application of just 10 per cent carbamide peroxide gel on teeth (35 per cent carbamide peroxide gel can be purchased online) reduces the enamel protein content by up to 50 per cent.

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

A recommended application of just 10 per cent carbamide peroxide gel on teeth reduces the enamel protein content by up to 50 per cent

Bozec had been looking at the effect of using hydrogen peroxide in root canal treatment prior to this study and found that it was causing damage to collagen locally. This led him to investigate how peroxide penetrates through the enamel and dentine before reaching the dental pulp – and checking what damage it may cause along the way. 

The study found that the loss of enamel protein content resulted in a greater penetration of the whitening agent inside the tooth, and can lead to an increase in dental pulp cell mortality. The team used an in-house dentine perfusion chamber to make their measurements. At carbamide peroxide concentrations around 35 per cent, the researchers found that dental pulp cells did not survive the exposure. 


A close-up through a microscope shows bare patches of a rough surface showing beneath more metallic-looking patches.
Applying carbamide peroxide gel on teeth in high concentrations can reduce the enamel protein content by up to 50 per cent (image courtesy of the Bozec Lab)

“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,” says Bozec. “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.”


While using a lower concentration would be less harmful, consumers often opt for increased concentrations to see an immediate effect

While using a lower concentration of peroxide – such as five per cent – would be less harmful to dental cells, consumers often opt for increased peroxide concentrations to see an immediate teeth-whitening effect. The study shows the need for a compromise between the concentrations of peroxide used, exposure time, desired patient outcomes and side effects experienced. This should be tested in-vivo prior to market release and patients should be made aware of the impact these procedures on their oral health, the researchers recommend.

“There is the potential to use either non-peroxide-based or a controlled peroxide release agent that will not cause the same damage,” says Bozec. “I believe that is the future of tooth-whitening.”

Bozec notes that the study, which included contributions from Boris Hinz, a distinguished professor at the Faculty of Dentistry, involved an international collaboration and the involvement students in the doctor of dental surgery program. They included Sabrina Nguyen and Ola Redha, a visiting PhD student from University College London.

“I worked with Professor Bozec previously at UCL for the last seven years and was fortunate to have him invite me to work on and complete this project here at the Faculty of Dentistry,” says Redha.

“It’s been fascinating to undertake research at the highest level at both U.K. and Canadian universities.”

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