IRA FLATOW: This is Science Friday. I’m Ira Flatow.

Raise your hand if you pay close attention to your teeth. Now raise your hand if you’re a parent of a teething infant. The difference becomes painfully obvious, doesn’t it? For you parents, while you impatiently wait for a baby’s teeth to poke through or soothe your fussy, teething toddler in the middle of the night, you might find yourself wondering why humans go through all this trouble for a set of teeth that are only temporary.

Then, of course one question can lead to another. Are baby and adult teeth made of the same stuff? Why can’t we just grow a new tooth if we lose one? And how did ancient people take care of their teeth? Did they have a dentist? Was there such a person?

We have questions and so do our kids, and we want to hear from them, too. So let us know what you’re curious about when it comes to your teeth. Here to tackle those tooth questions is a tooth scientist. She studies ancient human teeth to understand how humans evolved.

Dr. Shara Bailey is a Biological Anthropologist Associate Professor at New York University Dr. Bailey, welcome back to Science Friday.

SHARA BAILEY: Thanks for having me. I love being here

IRA FLATOW: It’s so nice to have you. Just a note to our listeners, we are recording this in front of a live Zoom audience. And if you want to be part of our next Zoom recording, join us. You can sign up at our website at sciencefriday.com/events.

All right Dr. Bailey, let’s clear up this first mouth mystery. What’s the difference between our teeth and our bones? Are they made of the same stuff?

SHARA BAILEY: Well the white part of your teeth that we see when we smile is made of enamel. Enamel is really, really hard and about 97% of it is made of minerals. And underneath the tooth enamel, you have something called dentin, which is very much like bone. So it’s about 80% or 70% mineral content. So it’s very similar in make up as bone. But the white part you see is different.

IRA FLATOW: Just as the inside of your bone is alive and living in your body, the inside of your teeth is alive and living.

SHARA BAILEY: Yes. Inside our teeth, we have nerves and blood vessels that are very, very much alive, as anyone who’s had a cavity filled or a root canal could certainly attest to.

IRA FLATOW: Ah– just thinking about it though

[LAUGHS]

I’m trying not to go there.

[SHARA LAUGHS]

Let’s talk about baby teeth now. Why have we evolved as humans to need adult teeth? Why can’t our baby teeth just grow with us?

SHARA BAILEY: That’s a good question. Well we’re really constrained by our evolutionary history. So all mammals, in fact, have baby teeth. And since humans are mammals, we just have that evolutionary baggage that we bring along with us. The reason why we can’t have just one set of teeth– are adult teeth– is because when we’re babies, we’re teeny. So we can’t have these big teeth in a teeny tiny mouth.

And so you’re born and you develop these baby teeth. But as you grow, of course your jaw gets bigger and you need bigger teeth.

IRA FLATOW: And of course on the opposite end of the spectrum, why can’t we keep regrowing our teeth as we lose them, the way sharks do?

SHARA BAILEY: Yeah that would be nice. But if you think about it, what do we use our teeth for compared to what sharks use their teeth for? We use our teeth to slice but also to grind. And if you’re going to be grinding things up, you need a bigger surface area and a thick enamel so they don’t wear down, and because of that, your body invests a lot of energy into making your teeth.

And the shark’s tooth– the body doesn’t invest a lot of energy in– making them. And so you’ve invested a lot of energy into making these teeth. You’re going to make them last as long as possible.

IRA FLATOW: Is there another animal that has teeth like ours that can remake them over and over again?

SHARA BAILEY: Not like ours. But like sharks, crocodiles and alligators can regrow their teeth– not as many times– maybe about 80 times over their lifespan. But all their teeth are just simple cones. They don’t have the cool mammal teeth that we have.

I’m going to revise that. Elephants regrow their teeth about six times and manatees can regrow their teeth more times than humans. But other than that, most mammals are just like humans. Or humans, I should say, are like most mammals.

IRA FLATOW: Yeah. Could humans modify our genes so we could grow a new set of teeth if we lose one?

SHARA BAILEY: They are working on that, yes. That’s something that scientists are actually working on. They’re trying to harness the genes that allow alligators to regrow their teeth. They’re experimenting and seeing if they can use it for regrowing teeth. If you get your teeth knocked out or something, they can alter the gene that would allow you to regrow. Because we retain the dental lamina, so we have the potential. All you need to do is insert a tooth bud and then just get the chemical process going– this interaction between molecules.

IRA FLATOW: That’s all you’ve got to do.

[LAUGHS]

SHARA BAILEY: That’s it. Easy peasy.

[LAUGHTER]

IRA FLATOW: All right, we have someone. Let’s go right to Liam from Louisville, Kentucky. He has a question about loose teeth. Hi, Liam.

LIAM: Hi, how are you?

IRA FLATOW: Hi. Fine, thank you. Go ahead.

LIAM: My question is, why do teeth move around so much before they fall out?

SHARA BAILEY: Oh, well when your adult teeth are growing, they produce this chemical signal that tells your baby teeth roots to basically go away. So your body actually breaks down the tooth root. And if you break down the tooth root enough, eventually you have no root left and then your tooth gets all wiggly, because it’s just being held in there by what’s called the periodontal ligament– big, fancy word for you– but that’s all that’s holding your tooth in once the tooth root is gone. And that’s why it’s so wiggly.

IRA FLATOW: Liam, were you like me? Do you like to play with your loose tooth if it’s falling out and try to wiggle it a little bit more, sort of help it a little?

LIAM: Yeah, I messed around when I was little.

IRA FLATOW: Yeah. Thanks for that question. That was great. You study human evolution by examining ancient teeth. What tales can the teeth tell?

SHARA BAILEY: Oh, they can tell us so many things. They can tell us about diet in the past– what kind of diets humans were actually eating. We can look at microscopic tooth wear to tell us something about diet.

We can look at pathology like cavities– the rate of cavities over time. And something a lot of people don’t know is that before people started farming about 10,000 years ago, people didn’t have to worry about cavities. You didn’t have to go to the dentist because their diets were mostly protein or whole grains. And they just didn’t have the sugary diets that we have today.

IRA FLATOW: Speaking of diets, can you tell how healthy they were from looking at their teeth?

SHARA BAILEY: Absolutely. Besides looking at cavities, you can look at gum disease, because gum disease affects the bone that holds in your tooth. So yeah, you can tell quite a bit about health from the teeth.

IRA FLATOW: Well thousands of years ago, people did not live as long as we are now, right? I mean, life expectancy would be in your 30s or 40s.

SHARA BAILEY: Yeah.

IRA FLATOW: Would you expect then that people kept their whole set of teeth up until their death, just in general?

SHARA BAILEY: A lot of them do, but a lot of them don’t. But they lose them not because of cavities, they lose them because of tooth wear.

Gosh, I wish I could share some pictures with you. I have one image that I love to show my students of an individual that wore their teeth all the way down, so everything was gone. It was just the roots, so basically they were chewing food on the roots of their teeth. It was amazing.

And that’s remarkable because in most cases, once you start wearing your teeth down to that amount, you develop abscesses which basically can kill you outside of modern medicine.

IRA FLATOW: (SHUDDERS) Do you have any idea what they were chewing on to wear it down that much?

SHARA BAILEY: Oh gosh, I don’t know.

IRA FLATOW: What kind of stuff would it be, grains?

SHARA BAILEY: Well you could be. This was something that was about 40,000 years old, so they were eating meat. But it’s possible that if you dry meat, it can become tougher. Or you can get grains, dirt, and things– that are more abrasive, and that can wear your teeth down quickly. Or it was just a very old individual.

IRA FLATOW: Speaking of old, what are some of the oldest teeth that have ever been found?

SHARA BAILEY: I’ve looked at those. The oldest human teeth would be about 6 or 7 million years old. I have not seen those, personally. But I have seen the ones from the species Ardipithecus, which are 4.4 million years old. That was cool to see.

IRA FLATOW: I’ll bet. Do you also find old baby teeth?

SHARA BAILEY: We do, sure. You don’t find them as often. You can imagine that when your baby teeth fall out, the root is gone so all you’re left with are these little teeny tiny tooth crowns. And they’re hard to recover from an archaeological site. They may be there, but people might not recognize them. And also they tend to get worn down, too. So when we do recover baby teeth, a lot of times they’re very worn.

IRA FLATOW: I’ll bet. And the oldest baby teeth that you have found?

SHARA BAILEY: Oh, that would be in the millions. It would be 3.4 million, I think– the oldest ones I’ve seen. I can’t remember if the Ardipithecus has any baby teeth.

IRA FLATOW: All right, let’s go to Dax from Phoenix– has a question about dinosaur teeth. Yeah, I want to know that. Dax, go ahead.

DAX: What? Ask my question? I’m going to have to look at it again. I can’t remember it.

IRA FLATOW: Take your time.

DAX: What did dinosaurs do to take care of their teeth?

IRA FLATOW: Ooh.

SHARA BAILEY: Ooh.

IRA FLATOW: Good question.

SHARA BAILEY: Dinosaurs probably had teeth that would be like alligators. They would replace their teeth if their teeth fell out. So they probably didn’t really have to take care of them. They were lucky. They just ate what they wanted to eat. When their tooth fell out, it grew back in no problem.

IRA FLATOW: I imagine you find baby dinosaur teeth also, somewhere along the line.

SHARA BAILEY: Somebody would. I haven’t.

[LAUGHS]

IRA FLATOW: Somebody would, yeah.

[LAUGHS]

Well let’s talk about the baby teeth a little bit more. When you study them, do they have the same forensic markers that adult teeth have?

SHARA BAILEY: Yeah they do. The front teeth– the incisor teeth– are much simpler. They’re smaller, of course, but they’re also simpler. But the baby molars do have the same kinds of characters that we recognize as being markers of certain geographic areas.

IRA FLATOW: Well when you come across some really old teeth, how do you tell whether it’s from an ancient human or some prehuman? Is it easy or very difficult to tell?

SHARA BAILEY: Well there are some very diagnostic characteristics. So for example, if I saw a baby tooth from a Neanderthal, I would be able to tell you it’s from a Neanderthal. I mean if I showed them to you, you’d say they look just like ours. But to a trained eye, you can see big differences.

And the same for earlier ones like Australopithecines. They have definitely some certain characteristics that would tell me that’s an ancient human. Absolutely.

IRA FLATOW: This is Science Friday from WNYC Studios, talking with Dr. Shara Bailey, Professor of Anthropology at New York University. And we don’t have to pull teeth with her. I had to get a bad joke in some place.

[LAUGHS]

Excuse me.

[LAUGHTER]

I looked at a skeletal picture of a baby’s head when I was researching this, and it was kind of shocking to see that the adult teeth are right behind the baby ones in a child, waiting to descend.

SHARA BAILEY: Freaky.

IRA FLATOW: Yeah, it is very freaky. It’s not obvious when you look at a kid that there’s two sets of teeth in their mouth and that they have a second set right behind that.

SHARA BAILEY: Yeah, absolutely. There was this chart when I was a kid in my dentist’s office. He had a very classic Schour and Massler chart from the 1950s that actually showed that. And I remember being fascinated by– maybe I should have paid attention to that. I knew I’d be interested in teeth. But I remember staring at that chart and being like, oh I’m 7 and that means these teeth are forming.

IRA FLATOW: Yeah. Do other kinds of primates have that same two set of teeth system as we do?

SHARA BAILEY: Absolutely. Not only that, but the number of teeth that we have– two incisors, one canine, two premolars, three molars on each side– that’s actually something we share with apes and old world monkeys. So our dental pattern is actually quite conserved. And then we have certain characters on our lower molars that are also seen in other apes, so we share a lot of things with chimpanzees.

IRA FLATOW: Yeah, and I know a number of children who, when they lost their baby teeth, did not have the same number of teeth coming back. They were sort of missing some of their adult teeth. And the orthodontist had to remove the teeth around a bit.

SHARA BAILEY: Yeah, there are certain hotspot areas in our dentition where, if you’re going to have teeth that don’t form– so right next to your main teeth here, these incisors, these incisors, your wisdom teeth, and your second bicuspids– are the ones that if they’re not going to form, that’s where it’s going to happen.

IRA FLATOW: Here’s a question from JV in Rockville, Maryland. Are teeth specific to individuals? Do you ever find identical teeth? I guess they’re asking like– fingerprints.

SHARA BAILEY: Yeah, that’s a really good question. Now if you have identical twins, their teeth are going to look a lot alike. But even in identical twins, the teeth might be a little bit different. And that’s because it’s not just our genes that determine what our teeth look like, but also our environment and the kinds of things that are going on around us, or in our environment, while our teeth are developing.

So for example, one twin might have smaller teeth than the other twin. But besides twins, teeth are pretty unique to each person.

IRA FLATOW: Do you have any idea why some of our molars are called wisdom teeth?

SHARA BAILEY: Yes. Yeah.

IRA FLATOW: Why is that?

SHARA BAILEY: Well because when they erupt, we’re supposed to be wise by then.

[LAUGHTER]

And the first permanent tooth that comes in is called your school tooth because when that comes in, you’re of age to go to school. And do you want to guess what the second molar is called? So you have your school tooth and your wisdom tooth. What do you think is in between?

IRA FLATOW: Your college tooth–

[LAUGHS]

Your adult tooth– your adolescent tooth– I don’t know. I give up.

SHARA BAILEY: It’s called your factory tooth because when that comes in, you’re old enough to work in a factory.

IRA FLATOW: Oh goodness.

SHARA BAILEY: That’s going back to the 1800s when these teeth were named.

IRA FLATOW: Are we calling it Silicon Valley tooth now?

SHARA BAILEY: Or something like that, yeah.

IRA FLATOW: And do they have a certain purpose or are they just filling up the rest of your mouth, as they should be? Because so many people have their wisdom teeth pulled out.

SHARA BAILEY: Yeah. We don’t really need the wisdom teeth so much.

IRA FLATOW: We don’t?

SHARA BAILEY: Not so much. Think about our diets. They’re so soft now. And in fact, that’s one of the problems. That’s why people have dental problems. Our jaws don’t develop like they should because we eat these really soft diets as we’re growing up. And so our jaws are small, which doesn’t give us enough space to erupt our teeth, which is why sometimes our teeth are impacted, which can be very dangerous.

If you don’t have your wisdom teeth, you survive to adulthood, you have babies. Nature is not selecting against you.

[LAUGHS]

IRA FLATOW: One last question about the ancient teeth because it fascinates me. If ancient people had good diets, do their teeth look in better shape than the crummy diets we have now?

SHARA BAILEY: Yes. Yes they do.

IRA FLATOW: No kidding.

SHARA BAILEY: They wore down faster because their diets were tougher, but I don’t see cavities. You don’t really see periodontal disease that much. No, their teeth are in good shape.

IRA FLATOW: So we don’t know if they had dentists that they went to, either, because–

SHARA BAILEY: They wouldn’t have made a living.

[LAUGHTER]

IRA FLATOW: That’s a good place to wrap up. Thank you very much for taking time to be with us.

SHARA BAILEY: You’re welcome. Thanks for having me.

IRA FLATOW: Dr. Shara Bailey, Associate Professor in the Department of Anthropology at New York University. Thanks to everybody out there in Zoom world for taking time to be with us today.

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