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Science Out Loud.

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Every day, we rely on a
substance that's harder

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than iron or steel, our teeth.

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[MUSIC PLAYING]

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So if teeth are
harder than steel,

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they must also be
harder than bone.

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And if they're harder
than bone, then

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why does your jaw,
which is made of bone,

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not crumble under
all that pressure?

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There's a bit of tissue called
the periodontal ligament,

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or PDL, around your
teeth under your gums.

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The PDL is a shock absorber,
cushioning your jawbone

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from all the chewing forces.

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OK, so far, so good.

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But what if your teeth
come in all funky?

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Sure, it looks kind of goofy.

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But that's not the only
reason that somebody

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might want to fix it.

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Funky teeth can interfere
with the way you talk

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and the way you eat.

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So how do we fix this?

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Well, we basically break
our mouths with braces,

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except it's actually our
bodies that do the breaking.

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The PDL has these cells
called mechanoreceptors.

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And when these cells detect
a force on your teeth

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that's too big, like
if you accidentally

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bite into your fork,
they signal the brain

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to stop biting down
before you hurt yourself.

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Braces tether your teeth,
pulling them together

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or pushing them apart.

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Either way, they're applying
a steady force to your teeth.

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And when mechanoreceptors
in the PDL

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sense this kind of smaller
but sustained force,

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they signal cells
called osteoclasts

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to the area, which spew out
acid and proteins to dissolve

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parts of your jawbone.

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Then the mechanoreceptors
signal osteoblasts to come.

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And those cells deposit
minerals that make bone.

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Osteoblasts rebuild the
jawbone in a new shape

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that lets the PDL hold
teeth in the new position.

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So braces basically
force your body

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to dissolve itself and
then rebuild itself

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according to their evil whims.

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Sounds barbaric, right?

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But your body is actually
breaking down and rebuilding

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bone using osteoclasts and
osteoblasts all the time,

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not just if you have braces.

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Bone remodeling is just
the way our body grows.

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The infant body replaces almost
all of its original skeleton

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by the time it's a year old.

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And it happens throughout
our entire life.

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10% of my bone
material is technically

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new since last year.

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We can manipulate the
bone remodeling process

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to not only get
straighter teeth,

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but also to treat diseases,
like osteoporosis, which

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make your bones very brittle.

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By keeping overactive
osteoclasts

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from dissolving
the bone so much,

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or by boosting osteoblasts
to produce more bone,

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drugs can prevent
bones in those patients

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from breaking so easily.

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People with severe
bone injury have

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to rely on bone transplants,
where they take bone

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from other parts of their body
and move it to the damaged

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area, which is sometimes
not even possible

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and is always painful.

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So instead, Paula
Hammond's group at MIT

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has created a new material--

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--that very slowly
releases proteins.

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And these proteins
cause osteoblasts

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to go right to the site
where the injury happened

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and generate new bone.

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Now, this was a really
big deal for us,

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because it's really hard to
generate something that very

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slowly releases the protein.

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Most of the time, the protein
comes out very rapidly

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and gets swept away in the
body, so that it no longer has

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any effect.

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It's easy to write braces off
as a form of medieval torture.

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But it's kind of amazing that
this mouth torture actually

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works.

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And the technology
that makes it possible

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is not just in your
braces, it's in your bones.

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Hi, my name is
Andrea, and thank you

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for watching this episode
of Science Out Loud.

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If you liked this episode,
why don't you check out

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some of these other videos.

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And visit our website.

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And visit our
website. [LAUGHING]

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They're separate things?

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