Hey smart people.

Joe here.

A couple of months ago, our son got his very first tooth.

And then for like 3 months, he still only had one tooth.

He looked adorable.

But also a little bit ridiculous.

Now this got me thinking… where do teeth even come from.

Like...how does that happen?

How do bones start growing out of our faces?

So, I did some research, and what I found… I’ll never be able to unsee.

And you probably won’t be able to unsee it either.

Let’s check it out!

Teeth are weird and awesome, and they grow in weird and awesome ways.

So where do they come from?

To understand that, we have to go way back.

Before you were even born.

Actually before you even had a brain… no.

I mean when you looked roughly like this.

Around three weeks into development, your body was just a flat little disc.

You were pretty two-dimensional.

Then you rolled yourself up into a tube.

It’s one of the most important things you’ve ever done!

So congrats on that.

The tube that forms from this embryonic origami is surrounded by incredibly important stem cells.

They migrate and build some of your most important parts – the spinal cord, brain, the bones in your middle ear to parts of your heart… and your teeth.

About 6 to 8 ___ weeks in, little groups of these cells form bumps under what will become your gums, and they undergo a transformation!

Some become odontoblasts – these cells make dentin, the tough, fibrous core of the tooth.

But the cells on top of those bumps transform too, into ameloblasts, the cells that build enamel, the hard outside layer of your teeth.

The process of building enamel is some awesome cellular nanotechnology, up in your face.

Enamel-building cells secrete a mixture of chemicals that hardens into mineral crystals.

The cell moves up, and secretes more mineral on top of the last layer.

Eventually the enamel-building cell dies off, leaving a long crystalline rod behind.

Millions of these rods packed together make up the enamel layer of your teeth.

This mineral is mostly hydroxyapatite – tough stuff that’s rich in calcium and phosphate.

Basically rocks, in your mouth.

And like rocks, they can last a really long time under the right conditions.

How long?

Would you believe thirty thousand years?

I'm here with Matt Brown he's the Director of the Texas Vertebrate Paleontology Collection.

What is that enormous thing right there?

This giant tooth right here is the canine tooth of a saber-toothed cat from an animal called Smilodon.

What's often called a saber-toothed tiger.

We're looking at this individual tooth that's fallen out of the skull.

When we look at a fossil like a regular bone other minerals have taken the place of that bone and it's sort of rock but this is pretty much enameled like the tooth the way that that cat grew it.

Yeah, what I'm holding here in my hand is pretty much what was walking around inside of the living Smilodon.

Got anymore old teeth for us to look at?

We sure do, we've got probably about a million of them.

So these are teeth from mastodons and you can see that these teeth here they look pretty familiar as teeth they look very similar to to even some of our molars.

This tooth here has a giant cavity in it just like my teeth we have got you can see the same thing in the fossil record.

It's a reminder that these animals were alive and walking around.

And the mastodon didn't brush their teeth.

That's probably the case.

Yeah.

I bet we can go even older.

We can.

This is part of the left side of the face of a Tyrannosaurus and we're looking at teeth here preserved in this skull that are about 70 million years old that tooth is not messing around but very clean much better dental health and they may have been brushing or maybe a meat diet is better for less cavities.

I bet we can go even older.

We sure can.

We're standing in front of a cabinet from the Jurassic period.

This is about a hundred ninety five million year old dinosaur called Dilophosaurus and we're looking at the enamel again.

All right You got anything older?

We do.

So our last stop is this cabinet here in the Pennsylvanian some of the oldest teeth that we have in this building with about 2 million fossils in it and so we're looking at a 300 million year old tooth with enamel that would be very very similar to the enamel that was swimming around in this animals mouth.

That is some long lasting teeth 300 million years old and that's unmistakably a shark tooth.

That'd make a killer necklace.

So building enamel is like making rocks in your mouth.

When all this enamel nano-fabrication is complete, your baby teeth finally bust out.

And they each leave behind an empty space.

And it’s here, thanks to stem cells, that the same tooth-growing process repeats to form your permanent teeth.

So, your baby teeth started growing even before you were born.

And by the time your baby teeth came in, your permanent teeth were already growing in behind them.

That means at one point your skull looked like this!

Yeah… it’s pure nightmare fuel.

Told you you wouldn’t be able to unsee it.

As your baby teeth feel those adult teeth growing in behind them, their root dissolves and they fall out.

Eventually you get between 28 and 32 teeth in your adult mouth.

But after those adult teeth grow in, all the stem cells that laid down the crystal nanorods self-destruct, so that’s the only set of replacement teeth you get.

But why don’t we keep our teeth-growing stem cells?

Scientists aren’t totally sure yet.

But maybe one day they could figure out a way to grow new teeth, and turn us into human sharks.

On second thought, maybe not.

Brushing and flossing is much less frightening.

So that’s how teeth grow.

Before you even had a brain, a special army of cells crawled to your head, and set up nano-crystal factories to basically build rocks inside your skull.

I think someone should tell the Tooth Fairy that THAT story is worth more than a dollar.