Your teeth are like a squad of superheroes inside your mouth. They help you crunch on carrot sticks, nibble popcorn and chew bubblegum. You’ve probably heard it’s important to brush your teeth to prevent cavities. But what is a cavity? And how do dentists fix them?

Join Molly and cohost Aya on a terrifically toothy adventure, as they explore what causes these pesky little holes in our teeth. They’ll meet a group of rowdy, party-loving bacteria and find out how sometimes, troublemaker bacteria in our mouths can cause cavities. Plus, dentist Dr. Jean Star will help explain how to fix cavities. All that, plus a brand new Mystery Sound!

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SUBJECT: You're listening to Brains On where we're serious about being curious.

SUBJECT: Brains On is supported in part by a grant from the National Science Foundation.

SUBJECT: All right. All right. Quiet down.


I said quiet down. Welcome to Camp Cozy Molars, the one and only summer camp for baby teeth.

SUBJECT: Oh, my gosh. Oh, my gosh. Summer camp. I'm going to paddle a canoe, and I'm going to make friendship bracelets.

SUBJECT: I'm going to discover my long lost tooth twin and hatch a plan to reunite our tooth parents with hilarious consequences.


SUBJECT: Settle down, baby teeth. I need all of your toothy focus on me. Now time for a Camp Cozy Molar tradition, telling scary stories around the campfire. Who's got a scary story?

SUBJECT: I've got one. It was a dark and stormy night. Taylor the tooth was getting ready for bed when she realized she was out of toothpaste.


SUBJECT: All right. All right. Let's not make these stories too scary. This is a summer camp for baby teeth after all, not adult teeth. Who's next?

SUBJECT: I have a scary story. It's called Picture Day. There once was a baby tooth named Tony. And Tony was very excited for picture day. He was sure his picture would be the very best, but one thing Tony the tooth didn't realize--


He has spinach stuck on him.


SUBJECT: The horror.


MOLLY BLOOM: You're listening to Brains On from APM Studios. I'm Molly Bloom, and I'm here with Aya from Atlanta, Georgia. Hi, Aya.

AYA: Hi, Molly.

MOLLY BLOOM: Today, we're talking all about our teeth, those amazing little appendages in our mouths that help us chew gum, nibble popcorn, and crunch on carrot sticks.

AYA: Our teeth also help us make sounds and form words.

MOLLY BLOOM: Right. You've probably heard that it's important to brush and floss your teeth because it helps prevent cavities. But what is a cavity? That's what our listener Bonnie was wondering.

BONNIE: Hi. My name is Bonnie, and I'm from Dallas, Texas. I was wondering, How do you get a cavity in your teeth? And how does the dentist fix it?

MOLLY BLOOM: So, Aya, What have you heard about cavities?

AYA: I've heard that they heard a lot and you have to go to the dentist to get them like fixed or treated.

MOLLY BLOOM: Have you ever gotten one?

AYA: No, I haven't gotten one. But I feel like I'm going to get one at least once in my life.

MOLLY BLOOM: Yeah. Most people do for sure. Have you lost any teeth yet?

AYA: Yeah. I've lost seven teeth, and I had to get two of them pulled out.

MOLLY BLOOM: Oh, wow. OK. So when-- How old were you when you lost your first tooth?

AYA: I was almost 8. I was 7.

MOLLY BLOOM: Have you kept all your baby teeth?

AYA: Yep.

MOLLY BLOOM: Yeah. I kept all my baby teeth growing up too. And I think they're somewhere in my parents' house still. A little box of teeth, totally normal thing.

AYA: Yeah, totally.

MOLLY BLOOM: How do you feel about going to the dentist?

AYA: Some people are scared about going to the dentist. But honestly, the dentist is not that bad. It's kind of fun because our dentist gives us toys after we're done, and it doesn't hurt. So--

MOLLY BLOOM: That's a great deal. So when you go to the dentist, which is your favorite part of the experience?

AYA: When they clean our mouths because they give us like a bunch of options of like toothpaste with marshmallow, strawberry, raspberry, chocolate, and I always choose chocolate because I love chocolate.

MOLLY BLOOM: I've never had chocolate toothpaste. That sounds great.

AYA: It is.

MOLLY BLOOM: Oh, I'm jealous. So what is your least favorite part of going to the dentist?

AYA: When like the dentist comes and uses all those tools to open your mouth and check and it kind of hurts to keep your mouth open for that long.

MOLLY BLOOM: Or when they ask you a question and you're like, [MUMBLING] and you can't really answer. It's a little awkward.

AYA: It is.

MOLLY BLOOM: We're going to talk about cavities in a bit. But we need some toothy background. When you're first born, we don't have any teeth at all. But by the time you're about 6 months old, you start getting your first baby teeth.

AYA: Over time, you'll get more and more baby teeth. And by the time you're about three years old, you'll have 20 of them.

MOLLY BLOOM: Humans, like most mammals, have two sets of teeth in their lives. So just a couple of years later, around age 5, you'll start losing your baby teeth and they'll be replaced by your larger adult teeth. Those teeth will last you a lifetime if you take care of them.

AYA: And here's something that might surprise you about your teeth. They have different layers, almost like a raw chicken egg.

MOLLY BLOOM: The outside layer of your tooth is called the enamel. It's like the shell on the outside of the egg, and it's the hardest substance in your body, even harder than your bones. Its job is to protect your tooth and keep it strong.

AYA: Underneath the enamel shell is a layer of something called dentin.

MOLLY BLOOM: You know how if you crack a raw egg, there's clear stuff inside? Well, the dentin layer is kind of like the clear part inside of the egg. But instead of being runny liquid, dentin is hard like bone. And that helps it protect the very inside of your tooth.

AYA: That very inside part is the third layer. It's called the pulp.

MOLLY BLOOM: The pulp is like the yellow yolk at the center of the egg, and it's full of blood and special cells called nerves.

AYA: The nerves help your teeth sense when something is very hot or very cold. So when you bite into a popsicle--

MOLLY BLOOM: The nerves inside your teeth send a message to your brain that says, whoa, that's cold.

AYA: The pulp at the center of each tooth is also really important because it brings blood to the tooth and helps keep it alive.

MOLLY BLOOM: Teeth aren't like hair or nails. They're actually living, feeling parts of your body.

AYA: Yeah. There's a lot going on inside your teeth that you can't see.

MOLLY BLOOM: And get this, there's also a lot of teeny tiny microscopic things living on your teeth that are invisible to the naked eye like bacteria.

AYA: What the what? We've got bacteria in our mouths?

MOLLY BLOOM: We sure do. All of us have millions of bacteria living on every surface inside our mouths, our tongues, our teeth, even the inside of our cheeks. It's like a big bacteria party in there that never stops.

AYA: A party? This I've got to see.

MOLLY BLOOM: Let's bust out the zoom ray and check it out.

SUBJECT: Zoom, zoom, zoom.


AYA: Whoa. This is a party. I'm guessing those are the bacteria.

BABS: Whee, whee. Anyone want to play pin the tail on the paramecium?

MOLLY BLOOM: Oh, yes. That's definitely a bacteria party.

AYA: Who knew there'd be so many different kinds? There are round ones, long, skinny bacteria that look like hot dogs, even ones shaped like corkscrews.

BABS: Excuse me. Hello. Over here.

AYA: Molly, I think that bacteria is trying to get your attention.

BABS: Molly. I thought I recognized your voice. Wow, wow, wow. Oh, it's such an honor to meet you. Big fan. Huge.

MOLLY BLOOM: Thank you.

BABS: Babbets Bacteria, but you can call me Babs.

AYA: Huh? I didn't realize bacteria listened to podcasts, or were so energetic.

BABS: Oh, we may be microscopic, but our appetite for high quality podcast content is ginormous. (SINGING) Ba-ba, ba-ba, ba-ba, ba-ba-ba, Brains On.

MOLLY BLOOM: Well, we're glad we ran into you because--

BABS: You wanted my recommendation for best party snacks because it's definitely cheese crunchies followed by sour gummy worms, followed by--

AYA: Actually, we wanted to talk with you because we're doing an episode all about why we get cavities, and we were just talking about how our mouths are full of bacteria.

BABS: Oh, yeah. That's true. All humans have bacteria in their mouths, and that's totally normal. Your mouths are the perfect place for us. Not too hot, not too cold, and lots and lots of spit, just like Goldilocks finding her perfect bed.

MOLLY BLOOM: Babs, I'm pretty sure the bed Goldilocks found wasn't full of spit.

BABS: Are you sure? Oh, I could have sworn it was.

AYA: Nope, definitely not.

BABS: Oh, well, agree to disagree. Like that old human saying goes, one person's trash is another person's perfect, warm, spitty bed. Anywho, having bacteria in your mouth might sound a little weird or creepy, but we do a ton of good stuff for your bodies.

MOLLY BLOOM: Oh, yeah. The bacteria in our mouths help us break down the food we eat so it's easier for us to digest.

BABS: Bingo. Also, helpful bacteria like me can fight off other less helpful bacteria like the kind that can cause diseases. And we even help boost your immune system to keep you healthy.

AYA: Sounds a lot like the bacteria that live in our stomach and guts. They help break down the food we eat and keep us healthy too.

MOLLY BLOOM: For sure. They do a lot of work to keep our bodies running smoothly.

BABS: Exactly. But for the record, those gut bacteria definitely aren't your biggest fans, Molly. They don't know your cat's name, Winslow, or your favorite healthy snack, cottage cheese.

AYA: Wow. Babs really is your number one fan, Molly.

MOLLY BLOOM: Hey, How did you know my cat's--

BABS: Molly, Aya, it's so nice to meet you, but I gotta wiggle. I'm up next for the bacteria karaoke contest, and I gotta go warm up these old pipes.

(SINGING) Oh, germs just wanna have fun

Oh, germs just wanna have fun

MOLLY BLOOM: OK. Let's zoom back out for a bit.

AYA: So we've got this big family of bacteria in our mouths having a party all the time. But how does all this connect back to cavities?

MOLLY BLOOM: Well, sometimes this family of bacteria gets thrown out of whack, and that can have a big impact on your teeth. But before we get to that, I've got something else for us to sink our teeth into. It's time for the--


SUBJECT: Mystery sound.

MOLLY BLOOM: Are you ready to hear it, Aya?

AYA: Yep.

MOLLY BLOOM: All right. Here it is.

What do you think?

AYA: OK. It kind of sounds maybe something you have to pull and then it goes down, but it keeps bouncing a little while or those door stop thingies that are like-- they have springs on them, kind of sounds like it rattling back and forth.

MOLLY BLOOM: Yes. I can totally hear that. Should we hear it again and see if we get any other thoughts?

AYA: Yes.

MOLLY BLOOM: OK. Here it is.

New ideas?

AYA: Maybe something like spinning, spinning and then landing and like keep spinning while it's landing a bit.

MOLLY BLOOM: These are all really good ideas. I have no idea what this is either. So what we've heard is something kind of-- there's like a bouncing sound.

AYA: Yeah, kind of.

MOLLY BLOOM: OK. Well, we're going to hear it again, get another chance to guess, and hear the answer after the credits.

AYA: So keep listening.


MOLLY BLOOM: Hey, friends. We're working on an episode all about matches, those incredible little wooden sticks that make fire when you strike them on a surface. And we want to hear from you. If you could come up with a new name for matches, What would it be? Maybe the flaming twig or the fire fairy. Aya, What do you think? Do you have a new name for matches?

AYA: Maybe like sparky sticks because like matches make sparks that eventually start fires.

MOLLY BLOOM: I like sparky sticks. That is much more descriptive because like the word matches is sort of a strange word. It doesn't really describe what it's doing, right?

AYA: Yeah. There's another meaning for match, so-- and sometimes it maybe be confusing.

MOLLY BLOOM: So sparky sticks it is. I love it. Well, listeners, record yourself telling us about your ideas for a better name for matches, send them to us at And while you're there, you can send us mystery sounds, drawings, and questions.

AYA: Like this one.

ABIGAIL: Hi. My name is Abigail. And my question is, Why are flags different in each country in the world? And how did the United States come up with our flag?


AYA: And keep listening.


MOLLY BLOOM: You're listening to Brains On. I'm Molly.

AYA: And I'm Aya.

MOLLY BLOOM: And holy molars, we're talking all about teeth, specifically, Why we get cavities?

AYA: Before the break, we learned that teeth have three layers just like an egg.

MOLLY BLOOM: Enamel is on the outside like the shell. Dentin is in the middle like the clear part of the egg. And the pulp is at the center of the tooth just like the yolk.

AYA: We also learned there's a ton of bacteria in our mouths. A lot of that bacteria is really helpful.

MOLLY BLOOM: Right. The kind of bacteria that breaks down food and keeps our immune systems healthy. But there's also other kinds of bacteria in our mouths, and some of these bacteria are troublemakers. Let's whip the zoom right out again and take a look.

SUBJECT: Zoom, zoom, zoom.

MOLLY BLOOM: Check out those dudes.


SUBJECT: Hey. You want a piece of me, tough guy?

SUBJECT: I will dance battle you right here, right now.

SUBJECT: Oh, I'm going to dance so hard you're not going to know what hit you. Nobody can cabbage patch like me.

SUBJECT: Well, my hips don't lie.

SUBJECT: I floss like nobody's business, the tooth kind and the dance kind.

AYA: Wow. I never thought I'd ever get to see a bacteria dance off. This could be a great Step Up sequel.

MOLLY BLOOM: Step Up Bacteria Boogie could be the next blockbuster hit. So, yes, as long as the bacteria in your mouth are moving and grooving around, it's really no problem. It becomes a problem when the troublemaker bacteria stick around for too long and start to take over.

AYA: Take over? So what are these troublemakers like? Do they wear matching leather jackets and jaywalk? Do they litter?

MOLLY BLOOM: These troublemaker bacteria do not wear matching leather jackets or jaywalk, but they do litter sort of. You see that group of troublemaker bacteria over there?


SUBJECT: You know we're bad.

SUBJECT: Real bad.

SUBJECT: Sha-boom.

AYA: Whoa. They look tough. And are they eating something?

MOLLY BLOOM: They're eating the sugar from the food we chew and any sweet drinks we sip. You see, it's not just us eating our food, the bacteria in our mouths eat it too. And bacteria love sugar.

SUBJECT: Sticky, sweet goodness. Eat up.


SUBJECT: Narly, dude. Litter, litter sugar dinner.

MOLLY BLOOM: The bacteria get lots of energy from eating the sugar in our food. And all this energy makes them poop out this sticky acid onto our teeth.

AYA: Ew. Acid littering. This is the worst kind of littering.

MOLLY BLOOM: Yeah. And it's not great for your teeth. All these sugar gobbling bacteria that stick to your teeth are called plaque. And when that plaque hardens, it's called tartar.

AYA: Oh, I've heard of both of those things from my dentist. I never knew it was bacteria.

MOLLY BLOOM: I know. And the more plaque and tartar that build up, the worse it is for your teeth. If this kind of bacteria hangs around and keeps snacking, they'll make more and more acid. And that acid can eventually eat a little hole in your tooth. That hole is called a cavity.

AYA: It's like the bacteria are using the acid to dig a tiny tunnel in your tooth.


SUBJECT: Did someone say dig?

SUBJECT: We love to dig. We dig it.

SUBJECT: Yeah. Almost as much as we love sugar.

MOLLY BLOOM: These guys are the worst. Let's zoom out, shall we?

AYA: Please.

MOLLY BLOOM: So that's how cavities form. The troublemaker bacteria get comfy and start eating the sugar in your mouth. Then they poop out acid, which starts to wear down the enamel on your teeth, and that makes a hole called a cavity.

AYA: We know bacteria like sugar. Are there other foods that can make cavities worse?

MOLLY BLOOM: Yeah. They especially love sweet sticky things like candies and caramel, but they also like starchy foods like potato chips or crackers that can get stuck in your teeth and hang out for a while.

AYA: Oh, makes sense. If the food sticks around, that means more time for the troublemaker bacteria to hang around.

MOLLY BLOOM: So to avoid getting a cavity, it's important to keep all those bacteria moving and grooving.

AYA: And you can keep the bacteria moving by brushing twice a day and flossing regularly.

MOLLY BLOOM: Exactly. Speaking of toothbrushes, Aya, if you could make the toothbrush of your dreams, What would it look like? Would it have special tools, a special name? What would it do? Tell me about it.

AYA: This is an interesting thing to think about. Maybe it could be-- it could look like a normal electric toothbrush, and then have two compartments. And one of the compartments could like hold little flosses in there since you said that flossing is really important. And then there would be another compartment so when you're done brushing, you would take the brush part and put it into the compartment. Take the floss out and attach it to a little hook thing, and then you can use the normal toothbrush and it can help you dig into the spots that you need to floss more.

MOLLY BLOOM: I love that. That is so useful. Sounds like an amazing design. I think maybe you should be an engineer when you grow up.

AYA: Maybe.

MOLLY BLOOM: So would this new fancy toothbrush have a special name?

AYA: Yeah. Shinerama, like to shine your teeth.

MOLLY BLOOM: Oh, yeah. I like it, the Shinerama. Well, we also asked listeners to describe the toothbrush of the future. And here's what they came up with.

SUBJECT: Hi. This is what my toothbrush would be. It would be like a robot with toothbrush arms and it would brush your teeth and do everything like put the toothpaste on and get it wet and stuff.

SUBJECT: Toothbrushes in the future are like vacuums that suck up all the bad things.

SUBJECT: And when it's time to put toothpaste on, the toothpaste comes out of the toothpaste compartment. And when it's time to use your mouthwash, the mouthwash comes out of the mouthwash compartment.

SUBJECT: I would make it fly. And it would already know that I wanted it to toothbrush. So it would be like it's 0 minutes. So it like already did it.

SUBJECT: And when you're all done brushing your teeth and washing your mouth out, it has speakers that remind you to floss.

SUBJECT: My future toothbrush would be a screen and a camera with your dentist on it and your dentist telling where you should brush your teeth.

SUBJECT: My toothbrush of the future would shapeshift to get different parts of your mouth while-- and go super fast.

SUBJECT: In the future, the toothbrushes are dentures and you can put them in your mouth. And they like shake and you put toothpaste in. And they do all the brushing for you.

SUBJECT: And the bristles are gray. And it comes with toothpaste and it's free.

SUBJECT: A toothbrush where if you had braces, it would send out little furry bits that would go under your braces and clean your teeth for you. And if you needed braces, it would just give you the braces without any pain.

SUBJECT: If in the mornings you forgot to brush your teeth, it would come to you and embarrass you in front of all your friends and brush your teeth for you.

SUBJECT: My toothbrush would had a built in mini TV so I could watch TV while I was brushing my teeth.

SUBJECT: Make something like a retainer, and then you would put it in your mouth. And then just press a button, and then it would clean all your teeth at the same time.

SUBJECT: I would be laying in my bed and I'd be listening to Brains On. And I really love it. And the toothbrush would be brushing my teeth and flossing. And it's so fun staying in my bed and sleeping.

MOLLY BLOOM: Giant smiles and thanks go out to Grace, Nikon, Kora, Dashel, Solomon, Katie, Cabane, Elenor, Lissa, Sierra, Lila, Andrew, and Adma for recording their brush-tastic ideas and sending them to us. So, Aya, Where were we?

AYA: So we know we can prevent cavities by brushing and flossing our teeth. But what about if we already have a cavity?

MOLLY BLOOM: Getting cavities is totally normal. Both kids and adults can get them. And most people have at least one in their lifetimes. But the good news is that cavities are super fixable.

AYA: Phew.

MOLLY BLOOM: Double phew. I talked to Dr. Jean Star about this. She's a pediatric dentist at the University of California, San Francisco, which means she's a dentist who works with kids. And she said if you have a cavity, the dentist will start by cleaning your teeth.

DR. JEAN STAR: So what the dentist does is they use a little tool to clean the tooth. So they clean the outside of the tooth and even clean a little bit of the inside of the tooth. And we look really closely to make sure there's no germs left in the tooth.

MOLLY BLOOM: The dentist can usually see the cavity just with their eyes or by using their special magnifying glasses. Once they find the hole, they fill it. And that's why it's called a filling.

DR. JEAN STAR: And then where the cavity germs have made a hole in the tooth or made the tooth not as strong, we replace that part of a tooth with a strong layer, sometimes I call it like a tooth play-doh. And what it does is it makes your tooth very, very, very strong in the spots where the cavity was, and it's even stronger than it was before.

MOLLY BLOOM: That strong layer of tooth play-doh is also called filling material, and it makes the tooth even stronger than it was before. And the best part, that cavity can't come back to the same exact spot where you put that tooth play-doh.

AYA: It's super protected.

MOLLY BLOOM: Right. It's also worth pointing out that some people get more cavities than others, and there are lots of different reasons for that.

DR. JEAN STAR: So it is a balance of all sorts of things. It's not only cleaning your teeth, but it's what you're eating. It's what types of germs are in your mouth that comes maybe from your family. And it has to do also with where you live and your water. There's a lot of things that go into cavities.

AYA: So there are lots of different things that can make some of us have more cavities than others. And some of those things are out of our control.

MOLLY BLOOM: But we do have control when it comes to taking care of our teeth.

AYA: That's the whole truth, and nothing but the tooth.


MOLLY BLOOM: Your teeth are living things with layers just like an egg.

AYA: All of us have millions of bacteria living in our mouths. A lot of that bacteria is really good and helps keep us healthy.

MOLLY BLOOM: But there's also troublemaker bacteria in your mouth, and these bacteria love to eat sugary stuff stuck in your teeth.

AYA: When they eat sugar, these bacteria poop out acid that can wear little holes in your teeth called cavities.

MOLLY BLOOM: Brushing and flossing your teeth help keep the bacteria from sitting in the same place for too long and making cavities.

AYA: But if you do get a cavity, the good news is that your dentist can fix it.

MOLLY BLOOM: That's it for this episode of Brains On.


AYA: Brains On is a non-profit public radio program.

MOLLY BLOOM: There are lots of ways to support the show. Head to

AYA: While you're there, you can send us mystery sounds, drawings, and questions.

MOLLY BLOOM: And you can subscribe to our Smarty Pass. It gives you a special ticket to Brains On universe bonus content plus ad free episodes.


OK. Aya, Are you ready to hear that mystery sound again?

AYA: Oh, yes.

MOLLY BLOOM: OK. Here it is.

So last time you thought maybe something's spinning and falling, something-- the little store stopper vibrating. What-- Do you have any new thoughts?

AYA: Honestly, I think I'm going to stick with my answers. I can't think of anything else.

MOLLY BLOOM: Yeah. I'm going to guess it's a tiny creature tap dancing in the kitchen on the counter like a teddy bear come to life. That's normal, right?

AYA: Sure.

MOLLY BLOOM: OK, sure. OK, cool. Should we hear the answer?

AYA: Yes.

MOLLY BLOOM: OK. Here it is.

STEPHANIE: My name is Stephanie, and I live in Victoria, Australia. That was the sound of me rolling a dice on a table.

MOLLY BLOOM: Oh, rolling a dice.

AYA: That makes a lot of sense.

MOLLY BLOOM: It does make a lot of sense. OK. I feel like we weren't that far off. You were saying something spinning and dropping.

AYA: Yeah.

MOLLY BLOOM: The dice was spinning in the air and dropping.

AYA: And then landing.

MOLLY BLOOM: And then landing. Exactly. So I think you were pretty close. Excellent mystery sound and excellent guessing.

Now it's time for the Brains honor roll. These are the kids who keep this show going with their questions, ideas, mystery sounds, drawings, and high-fives.





Bye, guys.

MOLLY BLOOM: We'll be back next week with more answers to your questions.

AYA: Thanks for listening.

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