Nanoparticles may help prevent tooth decay

Scientists have found a way to use nanoparticles to effectively break down plaque and wipe out more than 99.9 per cent of cavity-causing bacteria within minutes, an advance that may help better prevent tooth decay.
The bacteria that live in dental plaque and contribute to tooth decay often resist traditional antimicrobial treatment, as they can "hide" within a sticky biofilm matrix, a glue-like polymer scaffold.
Researchers at University of Pennsylvania took a more sophisticated approach.
Instead of applying an antimicrobial to the teeth, they took advantage of the pH-sensitive and enzyme-like properties of iron-containing nanoparticles to catalyse the activity of hydrogen peroxide, a commonly used natural antiseptic.

The activated hydrogen peroxide produced free radicals that were able to degrade the biofilm matrix and kill the bacteria within, significantly reducing plaque and preventing the tooth decay, or cavities, in an animal model.
"Even using a very low concentration of hydrogen peroxide, the process was incredibly effective at disrupting the biofilm," said Hyun Koo, from the University of Pennsylvania.

"Adding nanoparticles increased the efficiency of bacterial killing more than 5,000-fold," said Koo.
Previous research showed that iron oxide nanoparticles behave similarly to a peroxidase, an enzyme found naturally that catalyses oxidative reactions, often using hydrogen peroxide.
Researchers used these nanoparticles in an oral setting, as the oxidation of hydrogen peroxide produces free radicals that can kill bacteria.

They grew a biofilm containing the cavity-causing bacteria Streptococcus mutans on a tooth-enamel-like surface and then exposed it to sugar.
The nanoparticles adhered to the biofilm, were retained even after treatment stopped and could effectively catalyse hydrogen peroxide in acidic conditions, researchers found.
They also showed that the nanoparticles' reaction with a one per cent or less hydrogen peroxide solution was remarkably effective at killing bacteria, wiping out more than 99.9 per cent of the S mutans in the biofilm within five minutes, an efficacy more than 5,000 times greater than using hydrogen peroxide alone.
They demonstrated that the treatment regimen, involving a 30-second topical treatment of the nanoparticles followed by a 30-second treatment with hydrogen peroxide, could break down the biofilm matrix components, essentially removing the protective sticky scaffold.

Researchers applied the nanoparticles and hydrogen peroxide topically to the teeth of rats, which can develop tooth decay when infected with S mutans just as humans do.
Twice-a-day, one-minute treatments for three weeks significantly reduced the onset and severity of tooth decay, compared to the control or treatment with hydrogen peroxide alone. The researchers observed no adverse effects on the gum or oral soft tissues from the treatment.
The study appears in the journal Biomaterials.