Researchers who followed close to 5,500 elderly people over an 18-year period, found those who reported brushing their teeth less than once a day were up to 65 percent more likely to develop dementia than those who brushed daily.
Inflammation stoked by gum disease-related bacteria is implicated in a host of conditions including heart disease, stroke and diabetes.
And some studies have found that people with Alzheimer's disease, the most common form of dementia, have more gum disease-related bacteria in their brains than a person without Alzheimer's, said Paganini-Hill.
It's thought that gum disease bacteria might get into the brain causing inflammation and brain damage, she told Reuters Health.
So she and her team wanted to look at whether good dental health practices over the long term would predict better cognitive function in later life.
The researchers followed 5,468 residents of a Californian retirement community from 1992 to 2010. Most people in the study were white, well-educated, and relatively affluent. When the study began, participants ranged in age from 52 to 105, with an average age of 81.
All were free of dementia at the outset, when they answered questions about their dental health habits, the condition of their teeth and whether they wore dentures.
When the researchers followed-up 18 years later, they used interviews, medical records and in some cases death certificates to determine that 1,145 of the original group had been diagnosed with dementia.
Of 78 women who said they brushed their teeth less than once a day in 1992, 21 had dementia by 2010, or about one case per 3.7 women. In comparison, among those who brushed their teeth at least once a day, closer to one in every 4.5 women developed dementia. That translates to a 65-percent greater likelihood of dementia among those who brushed less than daily.
Among the men, the effect was less pronounced, with about one in six irregular brushers developing the disease - making them 22 percent more likely to have dementia than those who did brush daily. Statistically, however, the effect was so small it could have been due to chance, the researchers said.
There was a significant difference seen between men who had all, or at least most, of their teeth, or who wore dentures, and those who didn't - the latter group were almost twice as likely to develop dementia.
That effect was not seen in women, though.
Paginini-Hill could only speculate on the reasons for the different outcomes among men and women. Perhaps women wear their dentures more often than men, and they visit the dentist more frequently, she suggested.
The new findings, published in the Journal of the American Geriatrics Society, cannot prove that poor dental health can cause dementia.
Neglecting one's teeth might be an early sign of vulnerability to dementia, for instance, or some other factor could be influencing both conditions.
Still, this report "is really the first to look at the effect of actions like brushing and flossing your teeth," said Dr. Amber Watts, who studies the causes of dementia at the University of Kansas and was not involved in the research.
The new study does have some limitations. Paganini-Hill and her team looked at behavior and tooth count as a kind of proxy for oral health and gum disease. They didn't carry out any dental exams so they couldn't determine if people had gum disease or not.
And tooth loss isn't always related to gum disease, Watts noted. Head injury and malnutrition are also important causes of tooth loss in adults, and any of those might increase risk for dementia, she said.
"I would be reluctant to draw the conclusion that brushing your teeth would definitely prevent you from getting Alzheimer's disease," Watts said.
Yet despite the limitations, Watts said the study is an important step toward understanding how behavior might be linked to dementia.
"It's nice if this relationship holds true as there's something people can do (to reduce their chances of developing dementia)," said Paganini-Hill. "First, practice good oral health habits to prevent tooth loss and oral diseases. And second, if you do lose your teeth, wear dentures."
SOURCE: http://bit.ly/N5CCOu Journal of the American Geriatrics Society, online August 2, 2012.