Biomedical Engineering Reference
In-Depth Information
a
b
0
1
2
3
1
4
2
3
4
0
1
2
3
4
[
µ
m]
[
µ
m]
Fig. 5.24
AFM images of the scratch under 0.1-2.7 mN on the axial section of a human tooth: (
a
)
two-dimensional image; (
b
) three-dimensional image. The
circle
shows the starting point of the
scratch, and the
arrow
shows the scratch direction
The wear of enamel is inevitable because of the never-ending mastication
throughout human life. However, the lifetime of a healthy tooth can be quite long.
Reportedly, small cracks are commonly seen on the outer surface of teeth due to
occlusal forces [
26
]. But these cracks rarely lead to fracture, because the decussa-
tion of enamel rods promotes an increase in the resistance to crack extension [
27
].
In addition, the breaking up of HA crystallites in scratching is believed to be another
way to prevent the tooth from destroying from a crack. When the crack grows in the
enamel, high residual stress usually concentrates at the site of the crack head. In this
case, the enamel HA grains near the crack head may be broken up into smaller ones.
As a result, the residual stress is dissipated and the prolongation of the microcrack
is prevented. Therefore, since such behavior is beneficial to the excellent mechani-
cal properties of tooth enamel, it can be viewed as tooth enamel's self-protective
behavior during mastication.
5.6
Recovery of the Scratch in Remineralization
Remineralization is a process describing how the enamel absorbs some kinds of
minerals from the external environment [
28
]. Gao et al. [
19
] evaluated the effect of
remineralization treatment on the wear behavior of human early carious enamel,
showing that the hardness and density of carious enamel increased obviously. It can
be inferred that the surface of the tooth enamel might be changed and the mechani-
cal properties can be improved after the remineralization process. However, most
studies on the remineralization of tooth enamel were limited to caries enamel and
surface-softened enamel; the recovery of scratched enamel in remineralization has
not yet to be well addressed [
2
,
19
,
29
].
