The Deal

• $49 for a dental cleaning, four bitewing x-rays and an exam ($300 value)

Cavities: Portrait of an Enamel Assassin 

One primary purpose of a dental appointment is checking for cavities. To learn exactly how they form, read on.

Cavities—also known as dental caries or simply tooth decay—form as the direct result of two interplaying factors: food and bacteria. As soon as 20 minutes after a meal, more than 500 types of bacteria begin to feast on any refined sugar or starch they can find, producing a potent acid as a byproduct. Tooth enamel is considered the hardest substance in the human body, but if left alone for extended periods, this acid can easily bore its way past the enamel and into the inner layers of the tooth, which house nerves, blood vessels, and minerals worth approximately 25 cents on the fairies' black market. Cavities can be difficult to notice in time—many don’t exhibit pain in the early stages of development, and they often occur in hard-to-clean spots, such as the small crevices on the top of molars. What's more, unlike a child's missing tooth, enamel doesn't grow back. Once it's gone, it's gone forever.

In a study conducted in Warwickshire, England, fossilized records showed that only 8% of people living in the Iron Age experienced tooth decay—a stark contrast to today’s 48%. Granted, blacksmiths might have been able to forge strong toothpicks, but there's a larger culprit to blame: the influx of carbohydrates, sugars, and processed foods that became more common in later humans' diets. To counter the increase in oral ailments, dentistry evolved from a field that relied solely on bare-knuckle boxing matches to one that delicately treats decay as it appears, most often by removing the acid-eaten portions of the tooth and rebuilding the structure with a cement filling or crown. As always, however, the best offense is a good defense—dentists recommend brushing daily and visiting the office twice a year to prevent cavities from even forming.