Inspiration from the Wear of Human Teeth - Dental Biotribology - page 164

8.1.5 Unique Lubrication System

Apart from the above factors, the unique dental lubrication system also makes an
important contribution to the excellent wear resistance of human teeth. Two types of
lubrication mechanisms are in place during the wear process of teeth in the mouth.
One is the boundary lubrication caused by saliva, while the other is self-lubrication
by the organic matters and water within teeth.
An important function of saliva is to form a boundary lubrication system and
serve as a lubricant to help decrease the wear of teeth [ 21 ]. Results of our in vitro
wear tests [ 22 ] have shown that artifi cial saliva, a simulation of real saliva, can have
both cooling and lubricant effects during the wear process of teeth, and the risk of
tooth texture burn may be greatly reduced under an artifi cial saliva condition
compared to a dry condition. The lubricating mechanism of saliva is presumably
based on a full separation of the sliding surfaces by salivary fi lms [ 21 ], which can
be maintained within the clinical occlusal forces in the mouth.
In addition, given the fact that the enamel is composed of at least 5 vol% of
organic matters and water, maybe an additional lubricating mechanism is related to
the self-lubrication of human teeth. Results of in vitro wear tests [ 23 ] show that at
the early stage of friction, the friction coeffi cient of primary teeth was much lower
than that of permanent teeth. Further microexamination showed that compared with
permanent teeth, the density of enamel rods is smaller on the occlusal surface of
primary teeth. In other words, as a hard tissue in growth, primary teeth contain more
organic phase than permanent teeth. Thus, it could be inferred that a more remark-
able self-lubrication effect exists on the surface of primary teeth, and then a low
friction coeffi cient is maintained for a long period of time.
In summary, the ingenious systemic structure, natural surface coating, compact
and orderly microstructure, bioactive self-protection and repair capacity, and
unique lubrication system of human teeth all play an important role in increasing
the teeth's wear strength. Furthermore, an integrated effect of the above factors
offers human teeth superb antiwear behavior.

8.2 Inspiration from Human Teeth to Engineering

Antiwear Systems

Dental friction and wear are an inevitable lifetime process due to normal oral func-
tion. However, most adult teeth can satisfyingly serve for decades or even almost a
century, which is attributed to those excellent tribological properties. Therefore,
without a doubt, human teeth are a superior natural wearable system.
As discussed above, the excellent antiwear behavior of human teeth is mostly a
result of the integrated effect of their ingenious systemic structure, natural surface
coating, compact and orderly microstructure, bioactive self-protection and repair