Can a Root Canal Make You Sick? Where the Myth Came From

You need a root canal, and you read online that root canals cause cancer, or that a root-treated tooth slowly poisons your body. The root canal cancer myth does not hold up. It traces back to one dentist's experiments a hundred years ago, and research since has contradicted it.

Let me walk you through where the idea came from, why it failed, and what the real risk is.

Where did the root canal cancer myth come from?

In 1923 a dentist named Weston Price published his research as Dental Infections, Oral and Systemic. He took infected teeth out of his patients' mouths and placed them under the skin of rabbits. In one example from the book, a tooth from a patient with kidney disease went under a rabbit's skin. The rabbit developed kidney disease too. Price took results like this as proof that teeth spread illness through the body.

Price was the key promoter of the focal infection theory. It held that one small pocket of infection, often in a tooth, could seed disease anywhere else. According to the American Association of Endodontists (AAE), the theory led to an era of extractions, both to treat illness and to prevent it.

Why didn't Price's experiments hold up?

According to the AAE, Price's methods drew criticism at the time he published them. By the early 1930s, better designed studies had discredited his findings. A documentary called Root Cause later revived the claim. In 2019 the AAE, the American Dental Association and the American Association for Dental Research wrote to the streaming services hosting it. Their letter names what went wrong in the 1920s: poorly controlled experiments, non-sterile conditions, and results other researchers could not repeat.

A tooth pulled out through the mouth carries the mouth's bacteria with it. Place that tooth under a rabbit's skin without sterile handling, and you plant a dose of bacteria in tissue normally free of them. The rabbit can fall ill from that alone, whether or not the tooth ever had a root canal.

A proper control group is how you tell the difference. A second set of rabbits gets the same handling with teeth that should be harmless, and you compare the two. The AAE reports that a 1951 review in the Journal of the American Dental Association found the focal infection research lacking. Among the missing basics were proper control groups.

You may also see a claim that 97 percent of cancer patients have had a root canal. The AAE says that figure has never been published anywhere. Even a true version would prove little. The 2019 letter counts about 25 million root canals and related treatments a year, so many people with any illness have had one. Two things happening to the same person does not mean one caused the other.

What do newer studies find about root canals and illness?

Their results vary, and none shows a root canal causing illness.

Head and neck cancer. A 2013 study in JAMA Otolaryngology-Head and Neck Surgery compared 399 people newly diagnosed with head and neck cancer to 221 people without cancer. The cancer group had fewer root-treated teeth on average, 0.56 against 1.01. The researchers adjusted for smoking, alcohol, age and other factors. People in the top third for root-treated teeth then had 45 percent lower odds of cancer than the bottom third.

That result was not statistically significant: the range of likely values ran from 70 percent lower odds to no difference. So it does not prove a root canal protects you, though the AAE quotes it as a 45 percent reduced risk. It also shows no sign of higher risk, which is what the myth claims.

Heart disease. A 2017 study from Finland followed 473 adults from 1995 to 2015, about half of whom had heart disease at the start. People with at least one root-treated tooth had about half the risk of dying from heart and blood vessel disease.

A 2009 U.S. study found more heart disease in one group, people with 25 or more teeth reporting two or more root canals. Studies like these show two things travel together, not that one causes the other.

The infection itself. A long-running study followed 708 men for up to 32 years. In men aged 40 or younger, new infections at the tip of a tooth root were linked to developing heart disease. In older men, the study found no significant link.

What does a root canal actually remove?

Inside each tooth is the pulp, the soft tissue holding its nerve and blood vessels. Deep decay or a crack lets bacteria reach it. The pulp sits in a closed chamber of hard dentin, so the inflamed tissue swells against solid walls and, in time, dies.

With no blood flowing through that dead tissue, your immune system cannot reach the bacteria living in it. The infection works its way out through the tip of the root into the jawbone, where it can form an abscess.

A root canal removes the infected pulp, cleans and disinfects the canals, then fills and seals them. The tooth stays in place because living bone and gum still hold it. The AAE explains that the tissues around a fully developed tooth keep nourishing it. Our post on what happens during a root canal walks through each step.

So the myth has cause and effect backwards. The infection is the risk, and the root canal is how the infection comes out. The only other way to remove it is to take the tooth out. According to the AAE, an extraction lets bacteria into the bloodstream significantly more often than a root canal.

Can a root canal fail and make you sick?

A treated tooth can fail, and it is worth being straight about that. The AAE lists reasons a treated tooth does not heal or becomes infected again:

• a narrow or curved canal that was not treated the first time
• a crown placed too late, or a seal that let saliva leak back inside
• new decay, or a loose, cracked or broken crown or filling
• a crack in the tooth itself

A reinfected tooth is an infection like any other, and treating the tooth again is one way to get the bacteria out. In retreatment the old filling comes out, the canals are cleaned and checked for any that were missed, and the tooth is sealed again. If infection persists, the next step is surgery at the root tip or removing the tooth, which our post on tooth extraction covers.

Common questions about root canals and illness

Should I have my old root canal teeth removed to prevent illness?

The AAE says there is no valid scientific evidence linking root-treated teeth to disease elsewhere in the body. Pulling a comfortable, working root-treated tooth leaves a gap to replace and buys no protection. A tooth that hurts, swells or shows infection on an X-ray is different, and it needs an exam.

Can a failed root canal make you sick?

A reinfected tooth is an active infection and needs treatment, like any abscess. Signs the AAE lists include pain when you bite, swollen gums, or a pimple-like bump on the gum. Swelling that makes it hard to breathe or swallow needs the emergency room first.

What should you do if you are still unsure?

Bring what you read to your exam and ask about it. My goal is for you to truly understand your options without feeling overwhelmed, and the decision is yours.

Keeping the tooth with root canal therapy and removing it are both real choices. If the tooth is swollen or hurting now, see our dental emergency page. To ask a question first, call us at (540) 288-2800 or send a message through our contact page.