Germs Quiz: What Lives in Your Mouth?

A typical human mouth contains billions of bacteria. If you haven't brushed your teeth lately, you might well have more living there right now than there are people on Earth.

Scientists have identified more than 700 different species of microbes -- ultra-tiny living things such as bacteria -- that are in people's mouths.

There's no basis for this myth. The mouths of humans and dogs both have roughly the same number of bacteria. And there are more than 100 different germs in dog (and cat) saliva that can make you sick.

While it's true that the longer food is on the floor, the more germs it will pick up, the "5-second rule" isn't real.

Food starts to pick up germs from the moment it hits the floor. You're better off tossing it and eating something else.

It's not contagious. While bacteria can pass through saliva, gum disease typically develops if your teeth and gums aren't healthy.

If your mouth isn't healthy, you increase your risk for gum disease through repeated and lengthy exposure to someone who's got it. To help keep germs away, brush, floss, and use an antiseptic mouthwash daily.

You should never share it with someone else. The CDC says that raises your risk of getting an infection.

Studies show that germs may linger on lipstick, drinking glasses, band instruments, and other personal items.

Don't share them if you want to avoid picking up potentially harmful bacteria, viruses, or other microbes. 

The American Dental Association recommends that you rinse your toothbrush with tap water after you use it, then let it air dry. Keeping it in a closed container creates an ideal moist environment for the growth of bacteria.

The group suggests you get a new one every 3 to 4 months, or sooner if the bristles are frayed or after you're sick. Your toothbrush won't do a good job cleaning your teeth if it's worn down.

Rinsing with one not only keeps your breath fresh, it can also help reduce plaque, the film of bacteria that forms on your teeth. It lowers inflammation of your gums, too.

Many dentists recommend using an antiseptic mouthwash twice a day.

Research shows that it's linked to healthier gums and lower odds for tooth loss.

While some bacteria are bad for your teeth and gums, others play a key role in keeping them healthy. Researchers are exploring a potential new kind of toothpaste based on mouth bacteria that create enzymes that prevent plaque.

Most microbes in your mouth are part of a sticky film on your teeth known as plaque, which is the main cause of tooth decay. A single tooth can host 500 million bacteria. This is, of course, why you brush, floss, and use an antiseptic mouth rinse.

When you eat, the outer shell of your teeth, called enamel, can get weakened from acids given off by bacteria on your choppers. Fluoride in toothpaste and mouth rinses can help strengthen your enamel and prevent cavities.

Harmful bacteria in your mouth can lead to gum disease, which has been linked to a number of other diseases. It was once believed that the bacteria were the culprit, but researchers have begun to think that inflammation caused by the bacteria is the key factor.