Biomedical Engineering Reference
In-Depth Information
Fig. 3.24
Microstructure observation of the occlusal surface [
42
]: (
a
) primary tooth; (
b
) permanent
tooth of the young age; (
c
) permanent tooth of the middle age; (
d
) permanent tooth of the old age
To investigate the effect of the enamel's microstructure on friction and wear
behavior, we used LCSM to examine and compare the microstructures of human
teeth at different ages on both the occlusal surface and cross section. Typical photos
are shown in Figs.
3.24
and
3.25
. The cross section of human teeth specimen was
fi rst etched for 15 min with an aqueous 0.005 M citric acid solution and then was
examined by LCSM. It can be seen that on the occlusal surface, the primary teeth,
as a hard tissue in growth, display more organic phase (Fig.
3.24a
) and the density
of the enamel rods is smaller compared with the permanent teeth (Fig.
3.24b-d
).
This observation implies that primary tooth enamel possesses a better toughness
and lower shear resistance than those of permanent teeth. Therefore, a low coeffi -
cient of friction can be maintained for a long period of time at the early friction
stage, while a low wear resistance, represented by remarkable fl uctuation in the
coeffi cient, is observed at the later friction stage (Fig.
3.20
). Low shear resistance
