Biomedical Engineering Reference
In-Depth Information
reported that the process of demineralization could be reversed in its early stages by
the intake of calcium, phosphate, and fl uorine ions [
25
]. Hence, the remineralization
of the acid-eroded enamel in saliva medium should be a convenient and feasible
method to restore tooth lesions. Most studies focused on the contribution of remin-
eralization to enamel caries lesion treatments, and the work on the effect of remin-
eralization on enamel erosion lesions is still very limited. It has been reported that
the remineralization of the acid-eroded enamel signifi cantly differed from the caries
lesion remineralization of enamel [
26
]. With the increasing prevalence of dental
erosion, more and more attention has been paid to the remineralization of the acid-
eroded enamel. Reportedly, the surface of enamel softened by acidic beverages
could be rehardened by subsequent exposure to saliva or artifi cial saliva [
16
,
27
].
However, little effort has been made so far to investigate the microstructure and
microtribological properties of the remineralized enamel surface although they are
fundamental to validate the restorative outcomes of the acid-eroded enamel.
In this chapter, we investigate the friction and wear behavior of human teeth
under various conditions, such as dry condition, artifi cial saliva, food slurry, and
citric acid solution, using in vitro simulation testing to explore the effect of the oral
environment on the tribological behavior of human teeth. Furthermore, the erosion
behavior of human tooth enamel was investigated in citric acid solution, and the
remineralization behavior of acid-eroded enamel in artifi cial saliva was studied.
4.2
Effect of Saliva on the Friction and Wear
Behavior of Human Teeth
In this section, we investigate the lubricating effect of saliva on human teeth by
comparing the sliding wear behavior of human teeth under dry condition and artifi -
cial saliva lubrication (its composition is listed in Table
3.1
)
[
28
]. A 52100 steel ball
was used as the counterpart because it was easy to access.
In dry condition, when human teeth slide against a 52100 steel ball, typical varia-
tions in the friction coeffi cient, as a function of number of cycles, are shown in
Fig.
4.1
. Microscopic examination showed that the degradation of a human living
tooth could be divided into four stages. A lower tangential force and coeffi cient of
friction were obtained at the early stage (A-B). The coeffi cient was about 0.3 and
remained constant up to 1,000 cycles. The tooth structure was slightly pressed. No
detached particle was observed except for some slight scratches. The wear marks
had a shiny appearance. In the second stage, some white particles were gradually
detached at the two edges of the contact accompanied by a rapid increase in the coef-
fi cient of friction (B-C) from 0.3 to 1.2. More and more particles were detached. The
coeffi cient was not constant, but took a higher value at the fi nal stage (C-D) (between
0.8 and 1.2). Some dental tissue appeared brown or gelled due to friction heat at the
local zone. Particles were continuously detached, while some were pressed and bro-
ken during friction. An important feature at this stage was that some dental tissue
were burned and carbonized. Some local black areas with black debris were observed
