1
00:00:01,860 --> 00:00:05,830
SPEAKER: Eating is one of the
great pleasures and necessities

2
00:00:05,830 --> 00:00:07,100
of life.

3
00:00:07,100 --> 00:00:10,480
And to enjoy everything
from energy bars

4
00:00:10,480 --> 00:00:14,580
to apples we rely on one
part of our bodies to do

5
00:00:14,580 --> 00:00:16,710
an important job, our teeth.

6
00:00:20,070 --> 00:00:24,410
Teeth are the hardest
substances in our bodies.

7
00:00:24,410 --> 00:00:26,800
They're harder than
our bones and they're

8
00:00:26,800 --> 00:00:29,700
even harder than iron or steel.

9
00:00:29,700 --> 00:00:31,950
While we chew our
teeth experience

10
00:00:31,950 --> 00:00:34,520
forces of up to 225 pounds.

11
00:00:37,800 --> 00:00:40,760
So why doesn't our
jaw just crumble

12
00:00:40,760 --> 00:00:43,580
under all of those forces?

13
00:00:43,580 --> 00:00:45,900
Between your tooth
and your jaw bone

14
00:00:45,900 --> 00:00:47,720
there's a specialized
piece of tissue

15
00:00:47,720 --> 00:00:52,970
called the periodontal
ligament, or a PDL for short.

16
00:00:52,970 --> 00:00:55,510
The PDL can easily
absorb the normal forces

17
00:00:55,510 --> 00:01:00,130
that a tooth experiences when we
chew, say, an apple, cushioning

18
00:01:00,130 --> 00:01:03,910
or protecting our jaw
bone from our teeth.

19
00:01:03,910 --> 00:01:07,440
And inside the PDL there
are all kinds of cells.

20
00:01:07,440 --> 00:01:10,820
One type called
mechanoreceptors sense forces

21
00:01:10,820 --> 00:01:12,910
of movement or pressure
applied to the tooth.

22
00:01:16,000 --> 00:01:20,280
Teeth sound like they're
already perfectly designed

23
00:01:20,280 --> 00:01:23,210
but sometimes we really
need to force them

24
00:01:23,210 --> 00:01:26,280
in a certain direction,
like with braces.

25
00:01:40,860 --> 00:01:45,890
As the braces slowly force
the teeth to move the PDL

26
00:01:45,890 --> 00:01:50,650
gets squeezed in one direction
and stretched in the other,

27
00:01:50,650 --> 00:01:52,510
kind of like a rubber band.

28
00:01:52,510 --> 00:01:54,320
Here's where it
gets interesting.

29
00:01:54,320 --> 00:01:56,610
To make room, the
mechanoreceptors

30
00:01:56,610 --> 00:02:00,720
in the PDL trigger
cells called osteoclasts

31
00:02:00,720 --> 00:02:03,160
that actually come
in and dissolve part

32
00:02:03,160 --> 00:02:05,820
of your jaw to make extra room.

33
00:02:05,820 --> 00:02:08,800
The mechanoreceptors also
trigger another kind of cell

34
00:02:08,800 --> 00:02:11,120
called an osteoblast,
which comes in

35
00:02:11,120 --> 00:02:13,940
and builds up part
of the jaw bone.

36
00:02:13,940 --> 00:02:17,410
This allows the PDL to get back
into its regular cushioning

37
00:02:17,410 --> 00:02:21,970
shape, thus holding the
tooth securely in position.

38
00:02:21,970 --> 00:02:26,360
So if braces use osteoblasts
to physically reposition teeth

39
00:02:26,360 --> 00:02:28,260
for cosmetic reasons,
what if we want

40
00:02:28,260 --> 00:02:31,820
to use them to replace
things in our bodies?

41
00:02:31,820 --> 00:02:34,050
Dental implants
replace teeth that

42
00:02:34,050 --> 00:02:37,970
are damaged or missing to
restore chewing function.

43
00:02:37,970 --> 00:02:40,600
And MIT engineers are
using the properties

44
00:02:40,600 --> 00:02:44,290
of osteoblasts and osteoclasts
that are already in our bodies

45
00:02:44,290 --> 00:02:47,310
to create a chemical
coding for these implants.

46
00:02:47,310 --> 00:02:49,450
Just like in a
mouth with braces,

47
00:02:49,450 --> 00:02:51,830
this coding helps
create natural bone

48
00:02:51,830 --> 00:02:55,010
to help lock the
implant into place.

49
00:02:55,010 --> 00:02:56,920
Your jaw isn't the
only place where

50
00:02:56,920 --> 00:02:58,940
these osteoblasts
and osteoclasts are

51
00:02:58,940 --> 00:03:00,780
altering your bone structure.

52
00:03:00,780 --> 00:03:03,670
In fact, this boney
remodeling process

53
00:03:03,670 --> 00:03:06,180
is happening throughout
your entire body.

54
00:03:06,180 --> 00:03:09,350
And these implants aren't
just limited to teeth.

55
00:03:09,350 --> 00:03:16,390
Doctors can replace knees,
hips, and even spinal disks.

56
00:03:16,390 --> 00:03:18,570
Right now these
implants are designed

57
00:03:18,570 --> 00:03:21,170
to have the exact same
functionality as the parts

58
00:03:21,170 --> 00:03:24,070
that they're replacing
but, in the future,

59
00:03:24,070 --> 00:03:28,400
scientists may even use
implants to improve our brains.

60
00:03:28,400 --> 00:03:32,470
Just like with braces, we
could modify our bodies

61
00:03:32,470 --> 00:03:35,850
to be more perfect.

62
00:03:35,850 --> 00:03:39,400
Once we've tasted the
forbidden fruit of perfection,

63
00:03:39,400 --> 00:03:41,670
will we still be human?