Judging from commercials, what the world wants is whiter teeth and fresh breath. But what we should really worry about, scientists say, is healthier gums.

That's because new research suggests a link between gum disease and Alzheimer's disease.

In a recent study by an international team of researchers -- including Associate Professor Lakshmyya Kesavalu of the University of Florida College of Dentistry --oral bacteria from poor dental hygiene was found in four out of 10 brain samples from patients who died of Alzheimer’s disease. It was not found in any samples from the brains of people who did not have the disease.

“This clearly shows that there is an association between oral bacteria and Alzheimer’s disease, but not causal association,” Kesavalu said.

PHOTOS: Perfecto Gastrobar's launches in Miami's Brickell district

Oral bacteria can enter the bloodstream during chewing, brushing and dental procedures. The bacteria, researchers believe, then travel to the brain and potentially lead to degeneration in brain tissue.

Ironically, flossing also can cause bacteria to enter the bloodstream. But dentists say that's a reason to floss gingerly but regularly. In healthy gums, flossing won't cause bleeding, and flossing will help keep the gums healthy.

“We see televised ads for toothbrushes and toothpaste every day, with no emphasis on flossing,” says Dr. Laurence Grayhills of the Florida Academy of General Dentistry. “Based upon my 30 years as a dentist, the general public is still largely unaware of [its] importance."

The study, published in July, follows work at UF on mice infected with four major periodontal pathogens. In that unpublished study, the researchers found the oral bacterium moved to the brain in the mice as well, further confirming the group’s research on humans.

Gingivitis is seen in 97 percent of the population, Kesavalu said. It is one of the most common diseases to affect humans, more so than even the common cold. Meanwhile, one in three U.S. seniors dies from Alzheimer’s or another form of dementia. In 2013 Alzheimer’s is projected to cost the country $203 billion, according to the Alzheimer’s Association.