Biomedical Engineering Reference
In-Depth Information
layer of HA crystal deposition was formed on the softened enamel surface after 12 h
of remineralization in artifi cial saliva, but its crystallinity was low and the crystal
growth direction was random and undefi ned. Also, compared with the original sur-
face, the friction coeffi cient of the remineralized surface fl uctuated more strongly,
suggesting that the remineralization deposit layer was uneven and rough (Fig.
4.35
).
Thus, the mineral deposition layer on the remineralized enamel surface was worn
out more easily than the original enamel surface. The acid-eroded enamel surface
was rehardened and its wear resistance was improved by remineralization in artifi -
cial saliva, but the erosion lesions in the enamel could not be totally repaired. Given
that the remains of the enamel surface should be mostly soft organic substances
after 10 min of erosion in citric acid solution, the honeycomb-like structure might
be related to a form of solid lubrication. Therefore, the friction coeffi cient tended to
be a little lower on the eroded surface than on the remineralized surface, as shown
in Fig.
4.34
.
Increasing attention is being paid to the remineralization repair of the acid-
eroded enamel, and some studies on dental remineralization have been reported
recently [
66
-
68
]. Most of the related studies focused on the morphology change of
an enamel surface caused by remineralization, while research work on the microtri-
bological behaviour of the remineralized enamel surface is very limited. As dis-
cussed above, the crystal growth direction played an important role on the
microtribological behaviour of enamel. Analyses of the factors that infl uence the
growth of crystal were necessary to investigate the repair effect of remineralization
on the acid-eroded enamel. The growth of crystal is a very complicated course, and
it is infl uenced by various factors, such as the state of interface, vortex fl ow, tem-
perature, viscosity, crystallization rate, and so on. Among them, the state of inter-
face is very important. It has been reported that in the initial stage of erosion, when
a scaffold of mineral crystals is still remained, the lesions could be repaired by
remineralization [
26
,
69
]. Once the surface was completely lost, the erosion process
could not be reversed. In this study, when the acid erosion time reached 10 min, a
scaffold of mineral crystals still remained. In vitro remineralization in artifi cial
saliva happened. However, no satisfactory repair effect was observed. Since the
remineralization time of 12 h should be long enough in the mouth [
50
], it may be
necessary to shorten the acid erosion time in future research.
4.6
Concluding Remarks
In this chapter, we report on the in vitro wear tests we performed on human teeth
under various conditions, such as dry, artifi cial saliva, food slurry, and citric acid
solution, in order to explore the effect of the oral environment on the teeth's tribo-
logical behavior. Furthermore, the erosion behavior of enamel in citric acid and the
remineralization behavior of acid-eroded enamel in artifi cial saliva were also
