Nanoparticles carry the antibacterial drug farnesol to the surface of the teeth, where they release their payload when triggered by acidic environments.

Nanoparticles carry the antibacterial drug farnesol to the surface of the teeth, where they release their payload when triggered by acidic environments.

Michael Osadciw/University of Rochester

Plaque-busting nanoparticles could help fight tooth decay

Nanotechnology might soon save you a trip to the dentist. Researchers have developed tiny sphere-shaped particles that ferry a payload of bacteria-slaying drugs to the surface of the teeth, where they fight plaque and tooth decay on the spot. The approach could also be adapted to combat other plaquelike substances, known as biofilms, such as those that form on medical devices like orthopedic implants.

"It's quite clever," says oral microbiologist Robert Allaker of Queen Mary University of London, who was not involved with the research. "I think it was an innovative piece of work."

Plaque is a film made up of bacteria and a matrix of polymers composed of linked sugars, which clings tenaciously to teeth. When bacteria digest sugars in the mouth, they produce acid as a byproduct, which eats away at teeth, eventually causing decay. Topical antibacterial drugs don’t work well on plaque because saliva quickly washes them away.

Nanoparticles can solve this problem by clinging to the surface of teeth and carrying drugs along with them. Although this is not the first technique to employ such a strategy, the research improves upon previous methods, because these particles attach not only to the tooth, but also to the plaque biofilm.

To build their nanoparticles, the researchers assembled spheres of polymers composed of two segments with different characteristics. The outer segments are positively charged, allowing the spheres to attach to negatively charged sites of both the plaque biofilms and tooth enamel. The inner core reacts to high acidity in the mouth, which loosens up the nanospheres and preferentially releases their contents—the antibacterial drug farnesol—in decay-prone regions where it’s needed most.

The researchers initially tested the nanoparticles by creating a laboratory setup that mimicked plaque-covered teeth, using disks of a mineral found in tooth enamel, and culturing them with Streptococcus mutans, bacteria commonly found in plaque and one of the main culprits behind tooth decay. The team found that treatment with farnesol-carrying nanoparticles weakened the plaque's grip. Using a specially designed device to shear plaque off the disks, the researchers removed more than twice as much plaque from surfaces treated with farnesol-carrying nanoparticles as compared with those treated with farnesol alone.

In separate tests on rats infected with S. mutans, the team found that twice-daily applications of the nanoparticles reduced the severity and number of cavities plaguing the rodents’ teeth. Applying farnesol alone had negligible impact, the researchers report in ACS Nano.

This is the first time such a technique has been shown to be effective in animals, notes pharmaceutical scientist Dong Wang of the University of Nebraska Medical Center in Omaha, who was not involved with the research. “That's a huge step forward.”

Still, the method does have possible drawbacks, Wang cautions. Because the nanoparticles attach to biofilms instead of just to teeth, they could also bombard biofilms on the tongue or elsewhere in the mouth, where they may have damaging effects on beneficial bacteria. “We want to kill the bad guys but we don’t want to wipe out those that are helping us,” he says.

On the other hand, because the nanoparticles are nondiscriminating in their attraction to biofilms, the method could be generalized for tackling other dangerous biofilms, for instance, those that form on orthopedic implants or catheters, Wang says.

Before the nanoparticles make their way onto pharmacy shelves, they first must pass muster in human tests. Because the nanoparticles would likely be swallowed after they've done their work, researchers would have to ensure they didn't cause any ill effects.

Still, "it’s exciting to think about the possibilities,” says biomedical engineer Danielle Benoit of the University of Rochester in New York, one of the senior authors on the study. She suggests that these nanoparticles could be added to mouthwash, toothpaste, or gels that would be applied to the teeth. “We really believe that given a couple weeks [or months] of treatment, you would be able to get rid of the biofilm altogether,” reducing the need for dentists to scrape away plaque, Benoit says, “which would be awesome.”

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