# Why did my tooth fall out?

An episode of [Science for Kids / Science's Not Boring: The Kids Science Podcast](https://invisiblenetwork.ai/podcast/1896928296), 26 Aug 2026, 12 min.

Audio: https://www.buzzsprout.com/2624612/episodes/19669516-why-did-my-tooth-fall-out.mp3

Have you ever wondered why your teeth keep falling out, or how you get taller every single year? Get ready for a mind-blowing journey inside the hidden construction site of the human body! Did you know you actually started out smaller than the period at the end of this sentence? It is true! Join Mira and Finn as they explore the superhero builders in your bones called osteoblasts, and find out why you are actually taller in the morning than when you go to bed. (Hint: gravity squishes you down during the day!). Plus, we reveal the slightly spooky but completely amazing truth about baby teeth. Meet the tiny demolition crew called odontoclasts that actually dissolve the roots of your baby teeth so they can fall out! From human bones that are stronger than solid steel to astronauts growing two whole inches while floating in space, your body is doing incredible things even while you sleep. Tune in to find out how you get a brand-new skeleton every ten years!

## Transcript

[0:00] SPEAKER_00: Welcome to Science Is Not Boring by Kidopoly.com.
[0:03] SPEAKER_00: I'm Mira.
[0:04] SPEAKER_00: And I'm Finn.
[0:06] SPEAKER_00: Today, we are talking about something that happens to you every single day, even while you sleep.
[0:13] SPEAKER_00: We are talking about how your body grows.
[0:16] SPEAKER_01: And why my teeth keep falling out.
[0:18] SPEAKER_01: I just lost one last week, and I was a little freaked out to be honest.
[0:22] SPEAKER_01: Where does it go?
[0:25] SPEAKER_00: Don't worry, it's totally normal.
[0:27] SPEAKER_00: But before we get into the weird science of baby teeth, I have a mind-blowing fact for you.
[0:33] SPEAKER_00: Finn, did you know that you are actually taller right now than you will be tonight?
[0:38] SPEAKER_00: Wait, what?
[0:39] SPEAKER_00: That is impossible! Am I shrinking?
[0:42] SPEAKER_00: You kind of are.
[0:44] SPEAKER_00: Every morning, human beings are about 1 to 2 centimetres taller than they are at bedtime.
[0:49] SPEAKER_00: No way! Where does the extra height go?
[0:52] SPEAKER_00: Do my legs just squish down?
[0:54] SPEAKER_00: It is your spine! Throughout the day, gravity pulls down on you, and the soft cartilage discs between your 33 spine bones get squished.
[1:04] SPEAKER_00: When you lie down to sleep, they stretch back out.
[1:07] SPEAKER_01: So if I sleep standing up, I will stay short.
[1:11] SPEAKER_00: Probably.
[1:12] SPEAKER_00: But get this: NASA astronauts living on the International Space Station can grow up to 5 centimetres taller because microgravity from freefall makes them feel weightless, so nothing is squishing them down.
[1:25] SPEAKER_01: Whoa! Five centimetres?
[1:28] SPEAKER_01: That is like two whole inches! I need to go to space so I can finally reach the top shelf in the kitchen.
[1:34] SPEAKER_00: Okay, but let's go all the way back to the very beginning.
[1:38] SPEAKER_00: Before you were born, you started out as a single cell.
[1:43] SPEAKER_00: How small was I?
[1:44] SPEAKER_00: Like the size of a pea?
[1:47] SPEAKER_00: Way smaller! If you looked through a high-powered microscope, a human egg cell is only 0.1 millimeters across.
[1:55] SPEAKER_00: That is exactly the size of a period, or a full stop at the end of a sentence.
[2:01] SPEAKER_01: I was the size of a dot on a piece of paper.
[2:04] SPEAKER_00: Exactly! But today, your body is made up of about 30 to 40 trillion cells.
[2:11] SPEAKER_00: If you laid them all end to end, they would stretch around the earth multiple times.
[2:16] SPEAKER_01: 30 trillion?
[2:18] SPEAKER_01: That is a massive number.
[2:20] SPEAKER_01: How did I get so big?
[2:22] SPEAKER_00: That is the magic of growth.
[2:24] SPEAKER_00: Your body is basically a huge construction site, working 24-7 to build bones, muscles, and skin.
[2:32] SPEAKER_01: It definitely feels like a construction site when I get those weird growing pains in my legs at night.
[2:38] SPEAKER_00: Those are real! But despite the name, bone growth does not actually cause the pain.
[2:44] SPEAKER_00: It is really just muscle fatigue from active play and jumping around all day.
[2:49] SPEAKER_01: Wait, how do bones grow?
[2:51] SPEAKER_01: They are rock hard.
[2:53] SPEAKER_01: If my leg bone is solid, how does it get longer without snapping?
[2:57] SPEAKER_00: That is a brilliant question.
[2:59] SPEAKER_00: To figure that out, we have to zoom in on the ends of your bones, to a secret construction zone called the epiphyseal plate.
[3:07] unknown: Ha!
[3:07] SPEAKER_00: The epipher what plate?
[3:10] SPEAKER_00: The epiphysial plate! But scientists usually just call it the growth plate.
[3:15] SPEAKER_00: It is the place where the magic happens.
[3:17] SPEAKER_00: So where exactly are these growth plates?
[3:20] SPEAKER_00: They sit near the ends of your long bones, like your thigh bone.
[3:24] SPEAKER_00: Your thigh bone is called the femur, and it is actually the longest bone in your entire body.
[3:30] SPEAKER_01: Okay, so the growth plate is at the end.
[3:33] SPEAKER_01: What does it do?
[3:34] SPEAKER_00: Inside the growth plate, there are special cartilage cells called chondrocytes.
[3:40] SPEAKER_00: Think of them as squishy little bricklayers.
[3:44] SPEAKER_01: I like chondrocytes.
[3:45] SPEAKER_01: Do they work fast?
[3:47] SPEAKER_00: Very fast.
[3:48] SPEAKER_00: They constantly multiply and stack up like a tower of jelly bricks, pushing the ends of the bone further apart.
[3:55] SPEAKER_00: But jelly bricks would not hold me up.
[3:57] SPEAKER_00: I would be all wobbly.
[3:59] SPEAKER_00: Right.
[4:00] SPEAKER_00: So, as soon as the chondrocytes build the soft tower, another team of cells rushes in.
[4:06] SPEAKER_00: They are called osteoblasts.
[4:08] SPEAKER_01: Osteoblasts?
[4:10] SPEAKER_01: That sounds like a superhero team.
[4:13] SPEAKER_00: They kind of are.
[4:15] SPEAKER_00: Osteo means bone and blast means to build.
[4:18] SPEAKER_00: These osteoblasts pump out calcium and turn that soft jelly cartilage into rock-hard solid bone.
[4:26] SPEAKER_01: Whoa! So the soft cells push the bone longer and the hard cells cement it in place.
[4:32] SPEAKER_01: Exactly.
[4:33] SPEAKER_00: And this process can be incredibly fast.
[4:36] SPEAKER_00: Did you know a baby can grow about 10 inches or 25 centimetres in just their first year of life?
[4:43] SPEAKER_00: 10 inches in one year?
[4:45] SPEAKER_00: That is like adding a whole ruler to their height.
[4:48] SPEAKER_00: And during puberty, teenagers can have extreme growth spurts where they shoot up by 4 inches or 10 centimetres in a single year.
[4:59] SPEAKER_01: That explains why my shoes never fit for more than a few months.
[5:02] SPEAKER_01: My osteoblasts are working overtime.
[5:05] SPEAKER_00: Okay Finn, let's talk about the other crazy thing your body builds and then destroys.
[5:10] SPEAKER_00: Your teeth! Oh yeah!
[5:12] SPEAKER_01: I have a huge gap in my smile right now.
[5:16] SPEAKER_01: But why do we lose them at all?
[5:18] SPEAKER_01: Why not just grow big teeth from the start?
[5:21] SPEAKER_00: Imagine a tiny baby with massive adult teeth.
[5:24] SPEAKER_00: It would not fit in their small jaw.
[5:27] SPEAKER_00: Babies grow exactly 20 primary teeth, which we call baby teeth.
[5:32] SPEAKER_00: 20 sounds like plenty.
[5:34] SPEAKER_00: How many do adults have?
[5:36] SPEAKER_00: Adults need 32 permanent teeth.
[5:39] SPEAKER_00: As your head and jaw grow bigger, you literally run out of room.
[5:43] SPEAKER_00: So the body has to swap out the small set for a bigger set.
[5:47] SPEAKER_01: So how do the baby teeth fall out?
[5:49] SPEAKER_01: Do the adult teeth just push them like a bulldozer?
[5:53] SPEAKER_00: They do push, but there is a wild chemical demolition crew involved.
[5:57] SPEAKER_00: Remember the bone builders called osteoblasts?
[6:00] SPEAKER_01: Yeah, the superhero team.
[6:02] SPEAKER_00: Well, meet the demolition crew.
[6:04] SPEAKER_00: Odontoclasts.
[6:06] SPEAKER_00: Odonto means tooth, and clast means to break down.
[6:10] SPEAKER_00: Uh-oh.
[6:11] SPEAKER_01: What do they break down?
[6:12] SPEAKER_00: When an adult tooth starts pushing up, odontoclasts swarm the root of your baby tooth and literally dissolve it.
[6:20] SPEAKER_00: They eat away the root into the bloodstream.
[6:22] SPEAKER_01: They eat the root! That is slightly terrifying, but also amazing.
[6:27] SPEAKER_00: That is why when your baby tooth falls out, it is just the little white crown.
[6:32] SPEAKER_00: The long root that held it deep in your jaw is completely gone.
[6:36] SPEAKER_01: Wow! I always wondered why the tooth I put under my pillow did not have a pointy root on it.
[6:42] SPEAKER_01: The odontoclasts ate it.
[6:44] SPEAKER_00: It really shows how perfectly engineered the human body is.
[6:48] SPEAKER_00: The builders and the demolition crews work together to keep you strong and adapted to your size.
[6:54] SPEAKER_01: It matters a lot, right?
[6:56] SPEAKER_01: If we did not have growth plates, we would stay the size of a one-year-old forever.
[7:01] SPEAKER_00: Exactly! And speaking of engineering, did you know that tooth enamel, which is the white part on the outside of your teeth, is the hardest substance in the entire human body?
[7:12] SPEAKER_00: Harder than bone?
[7:14] SPEAKER_00: Yes.
[7:15] SPEAKER_00: It is mostly made of tough minerals and can withstand hundreds of pounds of pressure when you crunch down on an apple or a carrot.
[7:23] SPEAKER_00: What about our bones?
[7:25] SPEAKER_00: Are they strong too?
[7:27] SPEAKER_00: Oh, they are incredible! Ounce for ounce, human bone is actually stronger than solid steel.
[7:34] SPEAKER_01: Wait, my skeleton is stronger than steel.
[7:37] SPEAKER_00: Yes! A block of bone the size of a matchbox can support up to 18,000 pounds of weight.
[7:44] SPEAKER_00: That is like stacking two adult elephants on it.
[7:48] SPEAKER_01: That is mind-blowing.
[7:50] SPEAKER_01: I could carry elephants.
[7:51] SPEAKER_01: Well, my matchbox bone could.
[7:55] SPEAKER_00: Here is another wild fact.
[7:57] SPEAKER_00: Because your bone cells are always breaking down and rebuilding, you get a completely new skeleton roughly every ten years.
[8:05] SPEAKER_00: It is a process called bone remodelling.
[8:08] SPEAKER_01: Wait, you are telling me I get a brand new skeleton every ten years?
[8:13] SPEAKER_00: Yep.
[8:14] SPEAKER_00: The osteoblasts and their demolition partners, osteoclasts, are constantly recycling your bone tissue.
[8:20] SPEAKER_01: So I am basically a shape-shifting superhero.
[8:23] SPEAKER_01: This is the best day ever.
[8:25] SPEAKER_00: Alright, Finn, time for the quiz.
[8:27] SPEAKER_00: Are you ready to test your knowledge?
[8:29] SPEAKER_01: Okay, I'm ready.
[8:30] SPEAKER_01: I hope I remember all those wild science names.
[8:34] SPEAKER_01: First question.
[8:35] SPEAKER_00: How big is a human egg cell right at the very beginning before a baby starts growing?
[8:44] SPEAKER_00: Next one.
[8:45] SPEAKER_00: How many baby teeth do kids get in their very first primary set?
[8:54] SPEAKER_00: Question three.
[8:55] SPEAKER_00: What is the scientific name of the special demolition cells that dissolve the roots of your baby teeth?
[9:05] SPEAKER_00: Here's number four.
[9:06] SPEAKER_00: How many inches can a baby grow in just their first year of life?
[9:14] SPEAKER_00: Last question.
[9:16] SPEAKER_00: What is the name of the superhero bone-building cells that turn cartilage into solid bone?
[9:25] SPEAKER_00: Great job! Let's see how you did on the quiz today.
[9:29] SPEAKER_00: The first answer is, a human egg cell is about 0.1 millimeters across, which is exactly the size of a full stop.
[9:38] SPEAKER_00: For question 2, kids get exactly 20 baby teeth, which later get swapped out for 32 adult teeth.
[9:47] SPEAKER_00: Number three, the answer is, those wild demolition cells are called odontoclasts.
[9:54] SPEAKER_00: Question 4.
[9:55] SPEAKER_00: A baby can grow an incredible 10 inches or 25 centimetres in their first year.
[10:02] SPEAKER_00: And the final answer is, the bone-building superhero cells are called osteoblasts.
[10:08] SPEAKER_01: Wow, I did pretty well! I cannot believe how much weird stuff is happening inside my body right now.
[10:16] SPEAKER_00: It really is like a tiny hidden city working around the clock just to keep you growing.
[10:22] SPEAKER_01: I am definitely going to appreciate my osteoblasts more.
[10:27] SPEAKER_01: And I am checking my height tomorrow morning to see if I grew that extra centimetre.
[10:32] SPEAKER_00: That is a great experiment to try at home.
[10:35] SPEAKER_00: Hey listeners, if you loved learning about the hidden construction site inside your body, we would love it if you could leave us a five-star review.
[10:44] SPEAKER_01: Yeah, just scroll down on whatever app you are using and tap those five stars for the mighty osteoblasts.
[10:52] SPEAKER_00: Oh, and do not forget to head over to our site kidopoly.com.
[10:56] SPEAKER_00: We have got tons of fun learning games, cool activities, and more weird science to explore there.
[11:03] SPEAKER_01: It is the best place on the internet.
[11:05] SPEAKER_01: And if you want a shout out on the show, or just want to tell us your favourite weird science fact, send us an email at hello at kidopoly.com.
[11:15] SPEAKER_00: We love reading your messages.
[11:18] SPEAKER_00: Thanks for exploring the human body with us today.
[11:21] SPEAKER_00: Keep asking questions and keep growing.
[11:24] SPEAKER_00: See you next time on Science is Not Boring.
[11:27] SPEAKER_00: Bye, everyone!

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