Penn Dental prof uses nanoparticles to fight tooth decay

Nanotechnology may sound futuristic, but it has already found its way into household products, from cosmetics to cleaning solutions. And with a little help from a School of Dental Medicine scientist, consumers may one day even find nanoparticles in a tube of toothpaste.

A recent study co-led by Hyun (Michel) Koo, a professor in Penn Dental Medicine’s Department of Orthodontics, found that a cavity-fighting drug worked better when encapsulated in a nanoparticle carrier, dramatically reducing the severity and number of cavities in an animal model. The work was published last month in the journal ACS Nano.

The scientists’ goal was to kill cavity-causing bacteria by targeting dental plaque, a biofilm made up of bacteria enmeshed in a glue-like structure of extracellular polymers known as a polymeric matrix. When exposed to sugars—like those found in a tooth-decay promoting diet—dental plaque becomes acidic and wears tooth enamel away, causing cavities.

Though plenty of compounds can kill cavity-causing bacteria, it can be hard to keep them in the mouth long enough to have the desired effect.

“Usually orally delivered therapeutics are only transiently exposed to the mouth—think of a mouthwash or toothpaste in the mouth for only a couple of minutes at the most,” Koo says. “The problem was how to retain bioactive molecules on site to prevent or control oral biofilm formation.”

Koo’s colleagues from the University of Rochester, including bioengineer Danielle Benoit, were already at work on a drug-delivery mechanism Koo thought could be used against cavities.

“Danielle was using nanoparticles to deliver therapeutic agents to cancer cells that are presenting an acidic microenvironment, like plaque biofilms in the mouth when exposed to sugars,” Koo says. “That triggered the idea: We could use nanoparticles to develop a treatment for tooth decay.”

The research team designed a nanoparticle with a positively charged outer layer that would be attracted to tooth enamel and the biofilm matrix, and an inner layer to hold the drug—a compound called farnesol that is known to have antibacterial properties. The inner layer contained pH-responsive molecules that destabilize in acidic conditions, acting like a homing device to release the farnesol precisely when and where it is most needed.

The researchers applied the nanoparticle solution to the mouths of rats that had been infected with a microbe that causes tooth decay and were fed a cavity-promoting diet, rinsing their teeth twice daily for 30 seconds, just as a person might use a mouthwash morning and night.

Koo says the farnesol alone had no effect on the number of carious lesions, commonly referred to as cavities, and only a tiny effect on their severity.

“But with the nanoparticle, both the number and severity of dental caries was reduced,” he says.

Working with the Penn Center for Innovation, Koo has filed a patent on related technology. Earlier this year, a member of Koo’s lab, postdoctoral researcher Lizeng Gao, won the prestigious 2015 International Association for Dental Research Innovation in Oral Care Award for nanotech strategies to treat cavities. With further research into nanotechnology-based treatments, Koo says, “the ultimate goal is to take this to the clinic.”

Hyun Michel Koo