Stopping tooth decay before it starts -- without killing bacteria

Date:
August 17, 2020
Source:
American Chemical Society
Summary:
Eating sugar or other carbohydrates after dental cleanings causes
oral bacteria to quickly rebuild plaque and to produce acids that
corrode tooth enamel, leading to cavities. Today, scientists
report a treatment that could someday stop plaque and cavities
from forming in the first place, using a new type of cerium
nanoparticle formulation.



FULL STORY ==========================================================================
Oral bacteria are ready to spring into action the moment a dental
hygienist finishes scraping plaque off a patient's teeth. Eating sugar or
other carbohydrates causes the bacteria to quickly rebuild this tough
and sticky biofilm and to produce acids that corrode tooth enamel,
leading to cavities.

Scientists now report a treatment that could someday stop plaque and
cavities from forming in the first place, using a new type of cerium nanoparticle formulation that would be applied to teeth at the dentist's office.


==========================================================================
The researchers will present their progress toward this goal today at
the American Chemical Society (ACS) Fall 2020 Virtual Meeting & Expo.

The mouth contains more than 700 species of bacteria, says Russell
Pesavento, D.D.S., Ph.D., the project's principal investigator. They
include beneficial bacteria that help digest food or keep other microbes
in check. They also include harmful streptococcal species, including Streptococcus mutans. Soon after a cleaning, these bacteria stick to teeth
and begin multiplying. With sugar as an energy source and building block,
the microbes gradually form a tough film that can't easily be removed
by brushing. As the bacteria continue metabolizing sugar, they make acid byproducts that dissolve tooth enamel, paving the way for cavities.

Dentists and consumers can fight back with products including stannous
fluoride to inhibit plaque, and silver nitrate or silver diamine
fluoride to stop existing tooth decay. Researchers have also studied nanoparticles made of zinc oxide, copper oxide or silver to treat dental infections. Although bactericidal agents such as these have their place
in dentistry, repeated applications could lead to both stained teeth and bacterial resistance, according to Pesavento, who is at the University
of Illinois at Chicago. "Also, these agents are not selective, so they
kill many types of bacteria in your mouth, even good ones," he explains.

So, Pesavento wanted to find an alternative that wouldn't indiscriminately
kill bacteria in the mouth and that would help prevent tooth decay,
rather than treat cavities after the fact. He and his research group
turned to cerium oxide nanoparticles. Other teams had examined the
effects of various types of cerium oxide nanoparticles on microbes,
though only a few had looked at their effects on clinically relevant
bacteria under initial biofilm formation conditions.

Those that did so prepared their nanoparticles via oxidation-reduction reactions or pH-driven precipitation reactions, or bought nanoparticles
from commercial sources. Those prior formulations either had no effect
or even promoted biofilm growth in lab tests, he says.

But Pesavento persevered because the properties and behavior of
nanoparticles depend, at least partially, on how they're prepared. His
team produced their nanoparticles by dissolving ceric ammonium nitrate
or sulfate salts in water.

Other researchers had previously made the particles this way but
hadn't tested their effects on biofilms. When the researchers seeded polystyrene plates with S. mutans in growth media and fed the bacteria
sugar in the presence of the cerium oxide nanoparticle solution, they
found that the formulation reduced biofilm growth by 40% compared to
plates without the nanoparticles, though they weren't able to dislodge
existing biofilms. Under similar conditions, silver nitrate -- a known anti-cavity agent used by dentists -- showed no effect on biofilm growth.

"The advantage of our treatment is that it looks to be less harmful to
oral bacteria, in many cases not killing them," Pesavento says. Instead,
the nanoparticles merely prevented microbes from sticking to polystyrene surfaces and forming adherent biofilms. In addition, the nanoparticles' toxicity and metabolic effects in human oral cells in petri dishes were
less than those of silver nitrate.

Pesavento, who was awarded a patent in July, would like to combine
the nanoparticles with enamel-strengthening fluoride in a formulation
that dentists could paint on a patient's teeth. But, he notes, much
work must be done before that concept can be realized. For now, the
team is experimenting with coatings to stabilize the nanoparticles
at a neutral or slightly basic pH -- closer to the pH of saliva and
healthier for teeth than the present acidic solution. His team has also
begun working with bacteria linked to the development of gingivitis and
has found one particular coated nanoparticle that outcompeted stannous
fluoride in limiting the formation of adherent biofilms under similar conditions. Pesavento and his team will continue to test the treatment in
the presence of other bacterial strains typically present in the mouth,
as well as test its effects on human cells of the lower digestive tract
to gain a better sense of overall safety for patients.


========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


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Link to news story: https://www.sciencedaily.com/releases/2020/08/200817104311.htm

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