Ira Flatow: This is Science Friday, I'm Ira Flatow. Raise
your hand if you pay close attention to your teeth. Hmm?
Now raise your hand if you're a parent of a teething infant. The
difference becomes painfully obvious, doesn't it? For you
parents, do you impatiently wait for 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: Oh, it's so nice to have you. Just to 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,
yeah, 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: Oh, well, the white part of your teeth that we
see when we smile is made of enamel. And enamel is really,
really hard, and about 97% of it is made of minerals. And
underneath that tooth enamel, you have something called
dentine, which is very much like bone. So it's about 80% or 70%
mineral in content, so it's very similar in makeup as bone. But
the the white part, you see, that's different.
Ira Flatow: So just as your bone is really living in your body,
excuse me. 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, 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 root canal could certainly attest to.
Ira Flatow: Ah, just thinking about it, try not to go there.
[laughter] Let's talk about baby teeth now. Why have we evolved
as humans to need baby teeth? Why don't teeth just grow bigger
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 kind of
just have that evolutionary baggage that we bring along with
us. So, you know, the reason why we can't have just one set of
teeth or adult teeth is because of course, when we're babies,
we're teeny, right? 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, right, what do we use our teeth for compared to what a
shark's use their teeth for, right? 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, you need 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 it's just,
again: you invest a lot of energy into making these teeth,
you're gonna 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, you know, but, like sharks,
crocodiles, 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. So well, let's see. 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, other than that, most mammals are just like
humans—or humans, I should say, are like most mammals.
Ira Flatow: Yeah, could we 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 people, scientists are actually working on and trying
to harness the genes that allow alligators to regrow their teeth
and they're experimenting and seeing if they can use it for
regrowing teeth, if you get your tooth knocked out or something
they can do to 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 kind of interaction between
molecules.
Ira Flatow: That's all you gotta do.
Shara Bailey: That's it. Easy peasy. [laughter]
Ira Flatow: All right, we have someone from Louisville who
wants to—let's go right to Liam from Louisville, Kentucky 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: Ooh. Well, when your adult teeth are growing,
they produce this kind of chemical signal that tells your
baby teeth roots to basically go away. So your body actually
resorbs or, you know, just kind of 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 once the tooth root is gone, and that's
why it's so wiggly.
Ira Flatow: Liam, were you like me? Did you like to play with
your loose tooth as it's falling out and try to wiggle it a
little bit more? And then, you know, sort of help it a little?
Liam: Yeah, I would mess around when I was teething.
Ira Flatow: Yeah. Alright. 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 you know, 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 really sugary diets that we have today.
Ira Flatow: Can you tell about, speaking of diets, can you tell
about how healthy they were from looking at their teeth?
Shara Bailey: Absolutely. Yeah. I mean, besides looking at
cavities, you can look at gum disease, because gum disease
affects the bone that holds in your tooth. And 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 we are now, right? I mean, life expectancy would be in your
30s or 40s.
Shara Bailey: Yeah...
Ira Flatow: Would you expect that people kept their whole set
of teeth up until their death just in general?
Shara Bailey: They— 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. So I've seen some—Gosh, I would
wish I could share some pictures with you. I have one image 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.
Ira Flatow: 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 kinds of stuff would it be, I mean...
Shara Bailey: Well, you could be—No, this was something that
was about 40,000 years old. So they were eating meat. But it's
possible that you can, you know, if you dry meat, that can become
tougher, or you can get grains, dirt and things, and that
will—that's 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: Human teeth?
Ira Flatow: Yeah.
Shara Bailey: Yes, I've looked at those—Well, okay, not all of
them. The oldest human teeth would be about six or seven
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 and that was cool to see.
Ira Flatow: I'll bet. I mean, do you will also find old baby
teeth?
Shara Bailey: We do, sure! You don't find them as often, and
you can imagine that when your baby teeth fall out, the root is
gone, right? So all you're left with are these little teeny tiny
tooth crowns and they're hard to recover from an archeological
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, very worn.
Ira Flatow: And the oldest baby teeth that you have found?
Shara Bailey: Oh, that would be in the millions, it would be
3.4, I think are the oldest ones I've seen. I can't remember if
the Ardipithecus has any baby teeth.
Ira Flatow: Okay, let's go to Dax from Phoenix has a question
about dinosaur teeth. Yeah, I want to know that. Dax, go
ahead. Do you have a question?
Dax: Oh, my question. I'm going to have to look at it again. I
can't remember it.
Ira Flatow: Take your time, take your time.
Dax: What did dinosaurs do to take care of their teeth?
Shara Bailey: Oh, dinosaurs probably had teeth 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, 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. [laughter]
Ira Flatow: 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 not quite as—they're much simpler. They're smaller, of
course, but they're also simpler. But the molars, the
baby molars, do have the same kinds of geographic—the
characters that we recognize as being markers of certain
geographic areas.
Ira Flatow: When you come across some really old teeth, how do
you tell whether it's from an ancient human or some pre-human?
Is it easy or very difficult to tell?
Shara Bailey: a Neanderthal because they have very
distinctive, that, I mean, to you, probably, 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'd have definitely some certain
characteristics that would tell me that 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. Had
to get a dad joke in somplace, Dr. Bailey, excuse me. I looked
at a skeletal—I looked at a skeletal picture of a baby's
head when I was researching this. And you know, it was kind
of shocking to see that the adult teeth are right behind the
baby ones when, you know, when a child, waiting to descend.
Shara Bailey: Freaky.
Ira Flatow: It is very freaky, you know? It's not obvious when
you look at a kid that there's teeth, two sets of teeth in
their mouth, and that they have a second teeth, right, the
second set right behind that!
Shara Bailey: Yeah, absolutely. You know, there was this chart
when I was a kid in my dentist's office, he had a chart, it's a
very classic Schour and Massler chart from the 1950s that
actually showed that, and I remember being fascinated—but
maybe that was, you know, I should have paid attention to
that. I knew I'd be interested in teeth. But I remember staring
at that chart and be like, "Oh, I am seven, and that means these
teeth are forming."
Ira Flatow: Yeah. Do other primates, chimpanzees, 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, you know, two incisors, one canine, two
premolar, 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
have a lot of—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 move the teeth around a
bit.
Shara Bailey: Oh, yeah, 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 he's asking or she's asking like,
fingers, right, fingerprints?
Shara Bailey: Yeah, that's a really good question. Now, of
course, 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
they could, 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: Yeah!
Ira Flatow: Why is that?
Shara Bailey: Because when they erupt, we're supposed to be wise
by then. Yeah, yeah. So I got another thing though. So your
six, 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 you want to guess what the second molar is called?
So you have your school tooth, your wisdom tooth, what do you
think's in between?
Ira Flatow: Your college tooth? [laughter] Your adult tooth, or
your, your adolescent tooth? I don't know.
Shara Bailey: It's called—
Ira Flatow: I give up!
Shara Bailey: The factory tooth. Because when that comes in,
you're old enough to work in a factory.
Ira Flatow: Oh, goodness.
Shara Bailey: So we're going back to the 1800s when these
teeth were named?
Ira Flatow: Are we calling it the Silicon Valley tooth now,
or?
Shara Bailey: [laughter] Something like that, yeah.
Ira Flatow: Coder tooth? [laughter] 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: I mean, people—The thing is, think about our diets,
right? They're so soft now. And in fact, that's one of the
problems. That's why people have dental problems is because 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. But there's really no... if you don't have your
wisdom teeth, you survived to adulthood, you have babies,
there's nothing, you know, that nature is not selecting against
you.
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 kind of crummy diets we have
now?
Shara Bailey: Yes, yes, they do.
Ira Flatow: No kidding.
Shara Bailey: But besides, you know, they wore down faster,
because their teeth, their diets were tougher. But yeah, 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 were
into either?
Shara Bailey: They wouldn't have needed them.
Ira Flatow: Wow.
Shara Bailey: They wouldn't have made a living.
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. And thank
everybody out there in Zoom world for taking time to be with
us today. We're gonna take a break and when we come back,
we'll revisit one of our favorite charismatic creatures,
the thylacine. Is it still extinct? Just what is it? We'll
find out after this break. This is Science Friday from WNYC
Studios.