Tooth decay takes the cake as the most widespread disease on this list: According to the CDC, half of the 12- to 19-year-olds in the U.S. have tooth decay, and one quarter of all Americans aged 65 or older have lost all their teeth to the disease.
As any dentist will tell you, tooth decay comes from a combination of the mouth's natural bacteria and the leftovers of sugary food that remain on the teeth. The bacteria eat the sugars, producing acid that wears away the hard outer enamel of the teeth. Eventually, this can lead to cavities, periodontal infections and gum disease [source: ADA].
Preventing tooth decay can be as simple as brushing and flossing every day, or as sophisticated as sealing tooth enamel with acrylic sealants. On a wider scope, communities can reduce tooth decay by adding fluoride to their drinking water. However, only 27 U.S. states provide treated water to the majority of their residents, and rates of dental care are drastically lower for low-income populations than for middle- and upper-income groups [source: CDC]. With two-thirds of U.S. children from low-income families experiencing some level of tooth decay, we're a long way from wiping out this health condition.