Biomedical Engineering Reference
In-Depth Information
a
b
A
B
A
B
0
5
10
15
0
5
10
15
[
μ
m]
[
μ
m]
0.45
0.45
0.25
0.25
0.05
0.05
0.00
1.39
2.78
4.17
5.56
0.00
1.47
2.94
4.41
5.88
Length of AA/µm
Length of BB/µm
Fig. 4.19
Two-dimensional AFM micrograph of acid-eroded enamel surface and profi le of enamel
rod [
49
]: (
a
) after 3 min of erosion; (
b
) after 5 min of erosion
decreased signifi cantly after 2 min of erosion by citric acid solution at a pH of 3.25,
which was explained as a consequence of enamel surface demineralization.
More details were obtained from the profi les in Fig.
4.19
. As shown in Fig.
4.19a
,
some fl uctuations corresponding to substance loss were randomly distributed in the
profi le lines of an enamel rod after 3 min of erosion. Thus, some minute etch pits
probably occurred on the surfaces of enamel rods. The pits would not only destroy
the compact microstructure of enamel to lower the erosion resistance of enamel, but
also act as channels of the acid agent during the next erosion stage.
A signifi cant change in the surface morphology and an obvious substance loss
occurred with the further increase in the erosion period. As shown in Fig.
4.15d
, a
honeycomb-like morphology was observed on the surface of enamel after 5 min of
erosion. Moreover, a strong fl uctuation corresponding to uneven surfaces appeared
on the profi le lines (Fig.
4.16a
). There was an obvious increase in the erosion depth
after 5 min (Fig.
4.16b
). Subsequently, the depth presented almost a linear increase
with erosion time. Obviously, substance loss occurred with the further increase in
erosion time. Since enamel rods are highly mineralized in comparison with the sur-
rounding interrod enamel, the rods should be a weaker phase that can be easily dis-
solved during enamel erosion. Thus, a honeycomb-like structure was formed on the
surface of enamel. The occurrence of the honeycomb-like morphology suggested
that the enamel rods were dissolved to the extent that the compact microstructure of
the outer enamel was signifi cantly destroyed and its mineral substance was almost
lost. Being mostly soft organic substances, the remains of the outer enamel could be
easily removed by the impact action of acidic solution. Therefore, at the later stage
