A research group at the University of Illinois at Chicago (UIC) is using inorganic chemistry to solve a major challenge in clinical dentistry and oral medicine: preventing the plaque build-up on teeth that leads to cavities. The work was presented at the American Chemical Society’s virtual autumn 2020 meeting.

Tooth decay happens a result of bacteria in the mouth metabolising sugar in our food to produce acidic by-products. Left unchecked, the acids can corrode tooth enamel, which is comprised mostly of the calcium phosphate mineral hydroxyapatite. One of the problems is that the bacteria create a tough biofilm, known as plaque, that stubbornly adheres to the enamel and keeps the bacteria in close contact with teeth.

Now a UIC team, led by inorganic chemist and dentist Russell Pesavento, is aiming to use cerium oxide nanoparticles as a prophylactic step that will stop this plaque, and thus cavities, from forming on teeth. Hydroxyapatite-based nanoparticles are already used in some toothpaste formulations – but Pesavento and his colleagues wanted to capitalise on the chemistry of cerium.

Their tests have shown that cerium oxide nanoparticles can inhibit the formation of the biofilm on teeth, and now they are working on coating those same nanoparticles to make them more suited to oral applications. ‘We wanted to use an agent that can help prevent the biofilm from forming to begin with, not necessarily after the fact and after the tooth already begins to show signs of decay,’ Pesavento explained.

When the researchers seeded polystyrene plates with Streptococcus mutans – the bacteria most commonly associated with tooth decay – they found that the formulation reduced biofilm growth by 40% compared to plates without the nanoparticles. The presence of the cerium oxide nanoparticles led to ‘very weak’ biofilm that washed away off the plate, according to Pesavento.

Although the UIC team’s cerium oxide nanoparticles prevent microbes forming adherent biofilms, they do not actually kill the bacteria. That means the delicate balance within the complex oral microbiome – it is estimated that there are over 700 species of bacteria – is not disturbed.

Monalisa Mishra, a cell and developmental biologist at the National Institute of Technology Rourkela in India agrees that these cerium oxide nanoparticles could be used to inhibit biofilm growth in teeth. She suggests, however, that it would be preferable to investigate removal of existing biofilm on teeth. In addition, she emphasises that the possible toxicity of these cerium oxide nanoparticles if ingested must be thoroughly assessed.

The UIC researchers plan to test the potential toxicity of the nanoparticles using cell lines of the lower digestive tract. ‘That is our next set of studies,’ says Pesavento, ‘because [toxicity] is something that is very real and very possible … If you put something in the oral cavity, you are going to by default swallow some of it.’

Pesavento now has a patent for his cerium oxide nanoparticles, and one eventual goal is to combine them with enamel-strengthening fluoride in a formulation that dentists could paint on a patient’s teeth. The team is also experimenting with polymer coatings to stabilise the nanoparticles at a neutral or slightly basic pH conditions of saliva.