Biomedical Engineering Reference
In-Depth Information
4.5.3
Effect of Remineralization on Nanomechanical
Properties and Microtribological Behavior
of Acid-Eroded Human Tooth Enamel
In this study, we investigated the remineralization behavior of acid-eroded human
tooth enamel in vitro using artifi cial saliva to explore the repair effect of remineral-
ization on the antiwear properties of the acid-eroded enamel [
63
].
To investigate the contribution of remineralization to the repair of enamel ero-
sion lesions, we performed erosion tests and remineralization tests in sequence for
each specimen [
65
], as shown in Fig.
4.30
. Each specimen was fi rst exposed to
0.001 M citric acid solution (25 °C, pH = 3.20) agitated by a magnetic stirrer. After
10 min of erosion, the specimen was taken out and then carefully washed with
deionized water to remove any residual acid on its surface. In vitro remineraliza-
tion was conducted by immersing the acid-eroded enamel specimen in artifi cial
saliva (25 °C, pH = 7.00) for 12 h under slight stirring. To simulate real oral condi-
tions, the choice of these parameters was based on clinical experience and the lit-
erature [
39
,
40
,
50
]. In general, a low pH value can stay for a few minutes in the
mouth when people drink an acidic beverage [
39
,
40
]. The longest time interval
between two meals is about 12 h for most people. An important physiological role
of saliva in the mouth is the provision of a matrix for the remineralization because
it supplies calcium and phosphate ions for remineralization [
5
,
6
]. Both saliva and
artifi cial saliva were used as remineralization agents in prervious studies. It is dif-
fi cult to collect enough saliva because volunteers need to be stimulated by chewing
some specifi c things (such as gum, silicone tubing, etc.), and the saliva must be
donated by the same healthy individual and at the same time of the day so as to
escape individual differences. Hence, artifi cial saliva was used as the remineraliza-
tion medium in this study. Artifi cial saliva was prepared according to Wongkhantee
et al. [
64
], and its composition is listed in Table
4.4
. Three types of surfaces were
prepared for each specimen: The fi rst surface was the original surface without any
treatments (this surface was referred to as “original”); the second surface was the
acid-eroded surface (this surface was called “eroded”); and the third surface was
the remineralized surface (this surface was named “remineralized”), as shown in
Fig.
4.30
.
In this study, each tooth was cut into four parts along the buccolingual and
mesial-distal division lines. Each part was then embedded, ground, and polished to
obtain an enamel specimen with the exposed occlusal surface [
63
]. As a result, four
enamel specimens were prepared from a tooth. Two specimens were randomly
selected to conduct surface morphology examination and surface crystal character-
ization, respectively. The other two specimens were used to do nanoindentation
tests and nanoscratch tests, respectively.
The AFM micrographs of the original, eroded, and remineralized surfaces of
enamel are shown in Fig.
4.31
. The original surface of enamel appeared relatively
compact (Fig.
4.31a
). The enamel surface was destroyed badly after 10 min of ero-
sion in citric acid solution, and an obvious honeycomb-like structure appeared on
