Biomedical Engineering Reference
In-Depth Information
indicated in an overview on the function of saliva published by Mandel in 1987
[
104
], saliva is very important in preparing food for mastication, swallowing, nor-
mal taste perception, and lubricating and protecting the soft tissues and human
teeth. In addition, saliva is useful for soft tissue repair by reducing clotting time,
accelerating wound contraction, and maintaining the pH value in the oral cavity.
Results of in vitro wear tests that we carried out [
105
] have shown that artificial
saliva, a simulation of real saliva, can play both a cooling and lubricating effect dur-
ing the tooth wear process, and the risk of burning the tooth texture may be greatly
reduced under artificial saliva condition compared to dry conditions. Berg et al.
[
106
] measured normal and lateral forces between adsorbed salivary films for the
first time by colloidal probe atomic force microscopy. They found that the presence
of a salivary pellicle between hard surfaces reduces the friction coefficient by a fac-
tor of 20. This reduction in friction was consistent with the long-range purely repul-
sive nature of the normal forces acting between the salivary films. The lubricating
mechanism was presumably based on a full separation of the sliding surfaces by the
salivary films [
107
]. The friction between salivary films has also been investigated
at normal loads that cover the clinical jaw-closing forces, and it was concluded that
the lubricating properties are maintained within this load interval.
Efficient boundary-lubricating properties of human whole saliva in a soft hydro-
phobic rubbing contact, consisting of a poly(dimethysiloxane) (PDMS) ball and a
PDMS disk, have been identified by Bongaerts et al. [
107
]. Lubrication by saliva
resulted in a boundary friction coefficient of μ ≈ 0.02, two orders of magnitude
lower that that obtained for water. Dried saliva, on the other hand, resulted in
μ ≈ 2-3. Increasing the surface roughness increased the friction coefficient for saliva
while it decreased that for water. Therefore, understanding the lubricating proper-
ties of saliva might have implications for the development of saliva substitutes.
1.7
Early Methods of Cleaning Teeth
According to limited records from the literature and the Internet, different types of
toothpastes and toothbrushes were fabricated and used for cleaning teeth a long
time ago.
1.7.1
Toothpaste
In 2004, Bulgarian archeologists found a female skeleton believed to be 9,000 years
old. To their surprise, the skeleton possessed a nearly flawless set of teeth. The
archaeologists suspected that, in addition to her good genes, the female might have
used an early toothpaste-like concoction [
108
]. Another team of Viennese scientists
discovered an old Egyptian toothpaste formula that included rock salt mixed with
smaller amounts of mint, iris, and grains of pepper. All of the ingredients were
