Biomedical Engineering Reference
In-Depth Information
a
(a)
(b)
(c)
Contact position for different wear tests
b
1.0
0.8
b
0.6
0.4
c
a
0.2
0.0
1
10
100
1000
10000
Number of cycles
Variations of the friction coefficient at
different contact positions
Fig. 3.6
Friction behavior of the natural tooth in the axial section [
19
]
depth and area of the wear scars are bigger in the axial section than in the occlusal
section, as shown in Fig.
3.8
. The observations imply that it is more diffi cult for
brittle failure of enamel to occur in the occlusal section than in the axial section,
which is consistent with the research conducted by Xu et al. [
14
]. According to Xu
et al., for the occlusal section, most of the enamel rods appeared nearly perpendicu-
lar to the surface, while in the axial section, about half of the enamel rods appeared
nearly parallel to the surface, and the other half appeared angled to the surface.
Therefore, the anisotropic friction and wear behavior of enamel could be attributed
to the enamel rods' orientation. A similar phenomenon is observed at the dentin
zone due to the effect of the dentinal tubule orientation.
In addition, some researchers have pointed out [
30
,
31
] that due to different micro-
structures and mechanical properties, wear rates of enamel and dentin show a differ-
ent increase tendency as the load increases. A high mineral content and corresponding
hardness result in relatively low wear rates of enamel at lower loads; however, the
brittle nature of enamel contributes to a high wear rate at higher loads. By contrast,
dentin has a higher organic content and relative softness, which makes it less prone
