First, some caveats: It was a small study - just 10 brain samples from people who died of Alzheimer's, compared with 10 samples from people who died from other causes not dementia-related.
Also, the study, published in May in the Journal of Alzheimer's Disease, is associational, meaning the researchers didn't determine an exact cause-and-effect for how gum disease could play a role in developing Alzheimer's.
What they did find was a type of gum disease bacteria - Porphyromonas gingivalis - in four of the 10 Alzheimer's samples, but none in the 10 non-dementia samples.
The theory is that "bacteria in the mouth enter the bloodstream through chewing or tooth removal and end up in other parts of the body, including the brain," lead researcher StJohn Crean, dean of the School of Postgraduate Medical and Dental Education at the University of Central Lancashire, told Bloomberg News.
Chemicals produced by the bacteria then could build up, causing inflammation and contributing to the development of Alzheimer's, he explained.
Crean called the results of the study "very encouraging," but he added, "We've shown an association, not causation. It does nothing more than to prove that these bacteria do get to the brain."
It also doesn't address the question of whether people with advanced dementia simply have worse oral hygiene due to their cognitive state.
In the past, gum disease has been linked with heart disease, but an analysis of 500 studies last year by an American Heart Association expert panel could find no causal link.
So basically, it's still a good idea to floss to keep teeth and gums healthy and your breath odor-free, but whether skipping it will lead to more serious health problems, including dementia, remains to be proven.
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