The dreaded cavity is actually a little hole in your tooth caused by destruction of the hard outer enamel. Children are more likely to develop new cavities because they tend to consume more sugary foods and drinks that create bacterial plaque, a sticky film that produces enamel-eroding acids. However, 25% of adults between the ages of 20 and 64 have at least one untreated cavity. If a cavity is so microscopic your doctor catches it only on a routine X-ray. If the cavity is larger, you’ll need a filling. The most popular are composite, or plastic, ones designed to match the color of your teeth, and are usually covered by dental insurance. If you have a really large cavity, though, you may need a porcelain crown.