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Maintaining good oral hygiene is one way you can keep bad bacteria in your mouth from migrating to your brain. Getty Images

Rheumatoid arthritis and pneumonia are just two diseases that have been linked to gum disease.

According to a new study published in the journal Science Advances, bacteria normally present in the mouth can also release toxins that make their way into the brain. Once there, they may contribute to Alzheimer’s disease.

While dentists around the globe throw up their hands and say “Told you to brush twice a day!” here’s what’s going on and what you can do to protect your health.

Over 6 billion bacteria, including 700 different species, reside inside your mouth. Some promote health, others provoke disease.

“A reasonable estimate of the number of species that are ‘bad’ is roughly 15 to 20, but that will continue to evolve as we learn more about how these species interact with each other,” said Tara Fourre, research manager for global oral health innovation and microbiology at Johnson & Johnson.

Your mouth, or what scientists refer to as the oral microbiome, is “a complex community with lots of communication between bacteria of the same species as well as across species,” Fourre said.

When your teeth feel slimy and in need of a brushing, you’re feeling their presence.

Oral bacteria also thrive inside your cheeks and on your tongue, palate, tonsils, and gums. Your mouth is a great habitat for unicellular microorganisms. It’s constantly moist, has a fairly neutral pH, and a balmy temperature. But despite this perfect environment, not all the germs in your mouth stay put.

“Roughly two dozen oral species can be associated with diseases or conditions in other parts of the body,” Fourre said.

You swallow plenty of bacteria that end up in your gut, but your bloodstream is also a convenient form of transport. Each time you chew, brush, or floss, these germs get pushed into small vessels in your gums.

“Teeth are made of the same cell structure as bone,” said Mark Burhenne, DDS, founder of “They’re unique, however, in that they’re the only component of the body that breaks through skin with a bone at the base.”

The base of each of your teeth is protected by what’s called biological width.

“Think of it as a protective gasket where, in a healthy mouth, the immune system keeps bugs from entering the body and causing infection,” Burhenne said.

But when you have chronic gum disease or other oral infections, this seal breaks down.

“As oral bacteria breaks into the bloodstream, it can travel to organs throughout the body, including the brain,” Burhenne explained.

One known organism with the ability to cause harm in other parts of the body is Porphyromonas gingivalis, or Pg.

“Pg is full of surprises and deserves far more attention than it gets,” said Jan Potempa, PhD, DSc, a professor at the University of Louisville School of Dentistry, head of the department of microbiology at Jagiellonian University in Krakow, Poland, and a researcher for the study. “It’s a true gang leader converting good microbes into bad ones.”

Depending on where in the body it decides to go, Pg has been linked to a number of serious health issues, including pneumonia, rheumatoid arthritis, heart disease, hepatitis, and esophageal cancer.

Researchers now know it can sneak across the blood-brain barrier, a network of dense cells that protects the brain from harmful substances. Once there, Pg can cause pathological changes.

Potempa and other researchers observed Pg in the brains of deceased people with Alzheimer’s disease. But what was truly surprising was “finding Pg major proteins, called gingipains, in the brains at a level much higher than in mentally healthy people of the same age,” Potempa said.

And when mice were orally infected with Pg, the same DNA fingerprint was discovered in their brains, as well as the changes typically seen in people with Alzheimer’s disease.

“This result not only strongly supports that Pg brain infection may underline Alzheimer’s disease, but it pinpoints gingipains as major factors,” Potempa said.

In the study, Potempa and other researchers also tested the ability of an experimental drug known as COR388 to neutralize gingipains and block brain infection.

In animals who received it, “not only was the level of Pg DNA reduced, but also the pathology typical for [Alzheimer’s disease] did not develop in their brains,” Potempa said.

COR388 is currently in phase 1 clinical trials for Alzheimer’s disease. Separate studies are testing other ways to eradicate Pg, from antibodies that may keep it from spreading to a possible vaccine.

Scientists are also striving to understand more about “bad” bacteria in general. Johnson & Johnson is using donated saliva from its employees to try to replicate the oral microbiome and all 700 of its species in a lab.

In the meantime, “Migration of bacteria from one part of the body is a natural process. You can’t completely prevent it,” Fourre said. “But the number of bacteria that can get into the bloodstream may be reduced by improved oral care.”

“There are billions of bacteria in the mouth, and it’s important to keep it on the healthy side of the spectrum,” she said.

Here’s how to do so:

Brush and floss

And always do this for a full two minutes.

“By disorganizing the biofilm on your teeth when you brush, you’re able to prevent the acid attacks brought on by bad bacteria gathering on a particular area,” Burhenne said.

Flossing is just as important. It helps dislodge bits of food that would otherwise collect bacteria and contribute to inflammation and infection on the gums.

Go easy on the mouthwash

Burhenne doesn’t recommend mouthwash as part of a daily dental routine. “It’s too disruptive to the oral microbiome to allow for proper growth of good bacteria,” he said.

“Compare it to using antibiotics: On occasion, this may be helpful to get rid of infection, but if you’d use antibiotics all the time you’d eventually have no immune system left,” Burhenne added.

Eat more fruits and vegetables

A Veterans Affairs study of 625 men found that eating high-fiber foods, particularly fruits and vegetables, reduced the progression of gum disease. Fiber creates more saliva in the mouth, which helps get rid of excess food and offsets harmful acids.

Rinse with water after meals

Instead of reaching for the mouthwash, “[You’re] much better off to rinse your mouth with water after high-carb meals and snacks then brush 30 to 45 minutes later,” Burhenne said. “Water helps buffer the collection of bacteria until you can brush.”

Be vigilant if you already have a health issue

“People with certain diseases are more at risk for oral disease because they’ve already experienced a failure of the immune system,” Burhenne said. “It’s easy for some people to see dental or oral problems as a completely separate thing from other illness or disease, but that’s not how the body works.”