Today’s Wonder of the Day was inspired by Isabella from powell, OH. Isabella Wonders, “Why are teeth so hard?” Thanks for WONDERing with us, Isabella!

“Did you brush your teeth?" How many times each week do you hear that question? Do you take good care of your teeth? It's important to make sure you take good care of your teeth. They make eating and speaking much easier, and you need them your whole life. So that's why you're probably constantly being asked about your brushing habits.

Have you ever stopped to think about what your teeth are made of? They're obviously hard. So what's inside of them? What is it that makes up these things that enable you to chew your way through apples, pizza crusts, and all sorts of other great foods?

Teeth are a lot more complicated that they appear on the outside. The part you can see — called the crown — is just the tip of the iceberg when it comes to your teeth. There are all sorts of things going on below the surface!

Unlike many of your other body parts, your teeth develop in stages. When you were really young, you began to develop your baby teeth (also called primary teeth). These 20 teeth help you chew when you're young, but they begin to fall out starting around age five.

As your baby teeth fall out, they're replaced by your permanent teeth. When you finally lose all of your baby teeth around 12 or 13 years, there will be 28 permanent teeth in their place. Eventually, four more teeth — called wisdom teeth — will grow to complete your full adult set of 32 teeth.

Although it looks like you can see a lot of your teeth, all you really see is the hard exterior known as the crown. The crown is covered with a super-hard, shiny substance called enamel. The enamel is like body armor for your teeth, protecting their inner parts from damage.

How hard is enamel? Very hard! In fact, the enamel on your teeth is the hardest substance in your body! It's even harder than your bones.

Underneath the enamel is another hard substance called dentin. Most of the tooth is made up of dentin. Dentin isn't quite as hard as enamel, but it's still quite hard and does a good job of protecting the innermost part of the tooth, called the pulp. Dentin is about as hard as your bones.

The soft pulp is where the tooth's nerve endings can be found. It's also where the body's blood supply connects to the tooth to deliver necessary nutrients. If your teeth hurt from biting into something hot (or cold!) or a cavity, it's the nerve endings in the pulp that sense the pain and send messages to your brain about what's going on with your teeth.

The pulp reaches all the way underneath the gums to the root of the tooth. A tooth's roots are made up of a substance called cementum, which anchors each tooth to the jawbone.

Now that you know a bit more about what makes up your teeth, you might want to know why they're so important. Not only do they help you chew your food, but they also help you talk. It's true! If you think about the words you speak, you'll realize that many sounds you make every day are formed by the way your teeth interact with your lips and tongue!

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