Biomedical Engineering Reference
In-Depth Information
a
Sliding direction
(a)
(b)
(c)
(d)
(e)
Contact position for different wear tests
b
1.0
0.8
0.6
0.4
e
0.2
d
c
b
a
0.0
1
10
100
1000
10000
Number of cycles
Variations of the friction coefficient at different contact positions
Fig. 3.2
Friction behavior of the natural tooth parallel to the occlusal section [
19
]
force in the oral cavity ranges from 3-36 N [
22
]. Also reportedly, the loads applied
to the teeth during normal chewing are in the range of 10-20 N at the initial contact
[
23
,
24
] and are increased within the range of 50-150 N at the end of the chewing
cycle [
25
,
26
]. The magnitude of the force depends mainly upon the physical prop-
erties of food. As there are a great variety of foods, various forces can be expected.
In addition, the maximum biting forces vary according to gender, age, and muscle
build. Patients with bruxing habits can apply occlusal loads of approximately
1,000 N [
27
]. This work focused on the friction and wear behavior of human teeth
during normal chewing. Under the applied normal load of 20 N, according to
Hertzian contact theory [
28
], the associated mean contact pressure (208.0 MPa) was
below the yield strength of enamel (330 MPa) [
14
,
29
].
In the occlusal section, from the enamel to the dentin (Fig.
3.2a
), friction logs
describing the variation in the coeffi cient of friction, as a function of the number of
cycles, are shown in Fig.
3.2b
. Near the occlusal surface, an enamel layer of about
2 mm on the tooth crown showed excellent friction behavior. A lower friction coef-
fi cient was observed at the early stage. The coeffi cient was about 0.10 and remained
constant up to 1,600 cycles (Fig.
3.2b
). Then the coeffi cient increased rapidly to
0.80 and fi nally remained steady at about 0.85. With the enamel layer being thinned
by mechanical polishing, the evolution of the coeffi cient was found to be similar to
