Biomedical Engineering Reference
In-Depth Information
Fig. 3.5
Variations of wear
depth and hardness as a
function of the distance from
the enamel to the dentin zone
in the occlusal section [
19
]
400
100
Hardness
Depth
300
75
200
50
100
25
0
0
0
1
2
3
4
5
6
Distance (mm)
In addition to the wear resistance being different between different occlusal lay-
ers of enamel for a tooth, the friction coeffi cient also was observed to be different
between the outer and interior enamel in the occlusal section for a tooth, as shown
in Fig.
3.2
. Hence, it can be deduced that the friction and wear behavior of enamel
change from location to location for the same tooth.
In order to explore the effect of the microstructural orientation on the tribological
behavior of a human tooth, wear tests were also conducted with the same experi-
mental parameters in the axial section of a human tooth (Fig.
3.6a
). Three contact
zones, located at the enamel, DEJ, and dentin, respectively, were chosen. The varia-
tions in the friction coeffi cient in the three contact zones are shown in (Fig.
3.6b
).
For the enamel zone, the friction coeffi cient was about 0.26 before 10 cycles,
increased rapidly to 0.77 between 10 and 50 cycles, and then increased slowly to a
saturation value of 0.87 after 1,200 cycles (Fig.
3.6b
). In the DEJ zone, the coeffi -
cient increased rapidly at the early stage and then increased gradually to 0.97 from
10 cycles to 5,000 cycles (Fig.
3.6b
). However, for the dentin zone, the variation in
the coeffi cient fl uctuated between 0.3 and 0.5 before 500 cycles, and between 0.5
and 0.85 after 500 cycles (Fig.
3.6b
). The fl uctuations may be attributed to the spe-
cial dentin structure with a lacuna. There were more fl uctuations in the axial section
than in the occlusal section.
In the axial section, three different types of wear scars were also obtained from
the enamel to the dentin, as shown in Fig.
3.7
. It can be seen that the wear morpholo-
gies are similar to those of the scars observed in the occlusal section (Fig.
3.3
). The
main difference is that the wear depth of the scars in the axial section is bigger than
that of the scars in the occlusal section (Fig.
3.8
.).
Xu et al. reported a difference in the values of
H
and
E
of the enamel between the
occlusal and axial sections [
14
]. The graphs in Figs.
3.2
and
3.6
and the bars in
Fig.
3.8
demonstrate a signifi cant difference in the friction and wear behaviors
between the two orientations. First, the friction coeffi cient of the enamel generally
appears to remain at a low value for a longer time before increasing in the occlusal
section than in the axial section, as shown in Figs.
3.2
and
3.6
. Second, both the
