Women who want to get pregnant should brush their teeth and floss regularly as gum disease delays pregnancy, say experts.
Periodontal disease can delay the time it takes to conceive by two months on average, an effect similar to that of obesity in women, the European Society of Human Reproduction and Embryology (ESHRE) heard at its annual meeting.
The evidence comes from a medical study conducted in western Australia on a group of 3,416 pregnant woman, most of them young and of Asian background.
It took women with gum disease just over seven months to become pregnant, compared to an average five months for counterparts with healthy gums.
For non-Caucasian women with gum disease, the period increased to a year.
The study took other factors such as smoking and body weight into account.
The suspected culprit is inflammation caused by oral bacteria, which may have a knock-on effect on tissue in the reproductive system, doctors believe.
This is the first time gum disease has been identified among the factors that affect the chances of a pregnancy, said chief investigator Roger Hart, a professor of reproductive medicine at the University of Western Australia in Perth.
Hart cautioned that dental hygiene was only one part of "a whole package of healthy lifestyle."
"You have to make sure you're the appropriate weight, and many women need to lose weight, they need to stop smoking, they need to curtail alcohol to a minimum amount, they need to take folic acid, they need to ensure they've got the rubella [German measles] vaccination," he told AFP.
"But yes, if they've got gum disease, that should be treated."
Periodontal disease has been associated in previous research with miscarriage and premature birth, as well as heart disease, type 2 diabetes, respiratory and kidney disease.