Sandara Park: What's the hardest substance in your body?


	December 16, 2024

Original photo by Maryna Auramchuk/ iStock

Tooth enamel is the hardest substance in the human body.

The human body is a story of resilience. Wounds heal, bones regenerate, and our immune system fights diseases and infections, yet few parts of the body experience as many challenges as our teeth. Capable of biting, tearing, and grinding, teeth are designed to withstand (almost) anything humans consume, and evolution has provided Homo sapiens some help in the form of tooth enamel. Formed from a mineral known as calcium phosphate and arranged in a crystal lattice "woven" with threads 50 nanometers across (1,000 times smaller than a human hair), enamel is the hardest substance in the human body. Its lifelong mission is to protect the innermost layers of the tooth, including the dentin and tooth pulp (which contains all those nerves that give you a toothache).

A human's extra-strength set of chompers is useful for eating everything from warm soup to rock candy, but teeth aren't invincible. Modern diets ("modern" meaning after the agricultural revolution 10,000 years ago) are rich in carbohydrates, sucrose, and other sugars — much richer than what our hunter-gatherer ancestors experienced for hundreds of thousands of years. This new diet upset the well-balanced microbiome in our mouths, which are filled with around 700 kinds of bacteria. Some of these bacteria thrive on sugars, and left unchecked (i.e., without brushing, flossing, and regular dental visits), they attack enamel with lactic acid, a byproduct of the bacteria's metabolism. So while enamel is the hardest stuff found throughout the human body, it needs extra special attention to keep all 32 teeth covered in it healthy and strong.

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Snails have thousands of teeth.

Picture an animal sporting an impressive array of pearly whites, and something like a shark, whale, or lion might come to mind — but the humble snail outdoes them all. Depending on the species, snails have anywhere from 2,000 to 15,000 teeth in their pint-sized mouths. However, these teeth aren't the same as the hardened enamel in our own jaws. Instead, a snail's tongue (called a "radula") is essentially covered in rows and rows of tiny teeth that act like a file when the gastropod is munching on a meal. Because this wears down the teeth over time, they're regularly replaced. Yet some snail species also have incredibly tough teeth: The common limpet (Patella vulgata), for example, has teeth that are even stronger than spider silk, making them potentially the toughest biological material on the planet.

Today's edition of Interesting Facts was written by Darren Orf and edited by Bess Lovejoy.