Biomedical Engineering Reference
In-Depth Information
a
b
0
0
5
5
10
10
5
5
10
15
10
15
15
15
[µm]
[µm]
c
d
0
0
5
5
10
10
5
5
10
15
10
15
15
15
[µm]
[µm]
e
f
0
0
5
5
10
10
5
5
15
15
10
10
15
15
[µm]
[µm]
Fig. 4.15
Three-dimensional AFM micrograph of enamel surface subjected to different times of
erosion [
49
]: (
a
) before erosion; (
b
) 1 min; (
c
) 3 min; (
d
) 5 min; (
e
) 10 min; (
f
) 30 min
Variations in the calcium/phosphate ion content of the enamel surface with
erosion time are shown in Fig.
4.17
. Figure
4.18
gives the variation in the enamel
surface microhardness (
H
) with erosion time. As shown in Fig.
4.17
, the contents of
calcium and phosphate ions on the enamel surface decreased with erosion time. An
obvious decrease in
H
from about 347 HV before erosion to 292 HV after 3 min of
erosion was observed (Fig.
4.18
). Based on the fact that human tooth enamel is com-
posed of 92-96 wt% mineral substance [
10
], it may be inferred that a short-time acid
attack causes partial demineralization of the enamel surface, resulting in a remark-
able decrease in hardness. The inference is also supported by the nanoindentation
results of Lippert et al. [
50
]. They observed that the surface hardness of enamel
