TEETH

摘要

Our teeth say a lot. They reveal everything from our eating habits to our social habits. So open wide, and let's dive in.A mature human has a complete set of 32 teeth. Four types of teeth are nestled into our jaws: molars, premolars, canines and incisors, plus the optional wisdom teeth. Our array of teeth types means we are heterodonts, like most mammals. Homodont animals, by contrast, have the same type of teeth throughout their jaw, making their bite imprint look mostly uniform.Teeth, which grow in treelike rings, are made of enamel, the hardest substance in the human body. More than 300 types of bacteria live in the mouth, many of which can be found in dental plaque on the surface of the teeth.Teeth don't come with a lifetime guarantee, though. Because humans are diphyodont, we get only two successive sets of teeth throughout life. Other animals get way more: If they're polyphyodont, like sharks, their teeth are replaced continuously.