Biomedical Engineering Reference
In-Depth Information
Fig. 4.3
Profi le measurement
on the wear mark [
28
]:
(
a
) artifi cial saliva condition;
(
b
) dry condition
tooth surfaces observed in the dry testing mainly resulted from higher friction heat
at the local contact zone. Such a phenomenon is extremely unlikely to be repro-
duced in vivo because of natural saliva lubrication.
Berg et al. [
3
] measured normal and lateral forces between adsorbed salivary
fi lms for the fi rst time by colloidal probe atomic force microscopy. They found that
the presence of salivary pellicles between hard surfaces reduces the friction coeffi -
cient by a factor of 20. This reduction in friction was consistent with the long-range
purely repulsive nature of the normal forces acting between the salivary fi lms. The
lubricating mechanism was presumably based on a full separation of the sliding
surfaces by the salivary fi lms. The friction between salivary fi lms has also been
investigated at normal loads that cover the clinical jaw closing forces, and Berg's
group concluded that the lubricating properties are maintained within this load interval.
They also suggested that understanding the lubricating properties of saliva might
have implications for the development of saliva substitutes.
4.3
Effect of Food Particles and Occlusal Load
on the Friction and Wear Behavior of Human Teeth
In this section, we report on the in vitro friction-wear tests under two- and three-
body wear conditions on the occlusal surface of human teeth at different normal
loads, using a reciprocating apparatus (see Fig.
3.1
)
[
30
]. We paid particular atten-
tion to the effects of food particles and normal load on the tribological behavior of
teeth.
Flat samples used in this study were freshly extracted human teeth without caries.
A titanium alloy (TC4) ball was used as a ball sample. A reciprocating amplitude of
500
μ
m and a frequency of 2 Hz were used for all tests. Tests up to 2,000 cycles were
conducted continuously under two- and three-body wear conditions, respectively.
Three normal loads of 10, 20, and 40 N were used. Artifi cial saliva (its composition
