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PROFESSOR: Eating is one of the
great pleasures and necessities

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of life.

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And to enjoy everything
from energy bars to apples,

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we rely on one
part of our bodies

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to do an important
job-- our teeth.

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[TEETH CHATTERING]

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Teeth are the hardest
substances in our bodies.

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They're harder than our bones.

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And they're even harder
than iron or steel.

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So why doesn't our
jaw just crumble

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under all of those forces?

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Between your tooth
and your jawbone,

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there is a specialized piece of
tissue called the Periodontal

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Ligament, or PDL for short.

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The PDL can easily
absorb the normal forces

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that a tooth experiences when we
chew, say, an apple, cushioning

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or protecting our
jawbone from our teeth.

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Teeth sound like they're
already perfectly designed.

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But sometimes, we really
need to force them

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in a certain direction,
like with braces.

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As the braces slowly
force the teeth to move,

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the PDL is squeezed
in one direction

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and stretched in the other.

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To make room, the
mechanoreceptors

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in the PDL trigger
cells called osteoclasts

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that actually come
in and dissolve part

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of your jaw to make extra room.

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The mechanoreceptors also
trigger another kind of cell

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called an osteoblast,
which comes in

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and builds up part
of the jawbone.

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This allows the PDL to get back
into its regular cushioning

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shape, thus holding the
tooth securely in position.

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So if braces use osteoblasts
to physically reposition teeth

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for cosmetic reasons,
what if we want

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to use them to replace
things in our bodies?

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Dental implants
replace teeth that

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are damaged or missing to
restore chewing function.

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Your jaw isn't the
only place where

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these osteoblasts
and osteoclasts are

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altering your bone structure.

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In fact, this bony
remodeling process

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is happening throughout
your entire body.

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And these implants aren't
just limited to teeth.

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Doctors can replace knees,
hips, even spinal discs.

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And MIT engineers are
using the properties

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of osteoblasts and osteoclasts
that are already in our bodies

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to create a chemical
coating for these implants.

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Just like in a
mouth with braces,

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this coating helps
create natural bone

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to help lock the
implant into place.

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Right now, these
implants are designed

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to have the exact same
functionality as the parts

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that they're replacing.

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But scientists are already
developing implants

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to improve the performance
of our bodies and brains.

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So at that point, would we
be more machine than human?