Biomedical Engineering Reference
In-Depth Information
Fig. 5.22
(
a
) SEM image of the scratch on the axial section of a human tooth; (
b
) HA particles
outside the scratch area; (
c
) HA particles inside the scratch area
could estimate the maximum contact stress
P
0
on the contact area based on Hertzian
contact theory [
25
]:
1
3
=
æ
è
*
2
ö
6
EF
R
(5.2)
n
P
,
ç
÷
0
32
p
ø
1
-
u
2
1
-
u
2
1
(5.3)
=
1
+
2
.
*
E
E
E
1
2
Here,
F
n
is the normal load,
R
is the nominal radius of the tip, υ
i
is Poisson's
ratio, and
E
i
is Young's modulus. With
F
n
= 0.1 mN,
R
= 5 μm,
E
1
= 1,141 GPa,
E
2
= 90 GPa, υ
1
= 0.07, and υ
2
= 0.28 [
4
], the contact stress
P
0
was estimated as
1.84 GPa. This suggests that when the bite force is large enough during mastication,
the enamel surface will be deformed and the HA crystallites might be broken up into
smaller ones instead of cracks being generated.
