Biomedical Engineering Reference
In-Depth Information
Chapter 5
Microtribology of Human Teeth
5.1
Introduction
Due to its excellent mechanical and tribological behavior, enamel is one of those
unique natural substances that still cannot be substituted effectively with artificial
restorative materials. As shown in Fig.
5.1
, enamel uniquely consists of aligned
“prism-shaped” rods (4-8 μm in diameter), which run approximately perpendicular
from the dentin-enamel junction (DEJ) toward the tooth surface [
1
].
On the microstructure level, the enamel is constructed via enamel rods (abbrevi-
ated as “R”) and interrod enamel (abbreviated here as “IR”). As shown in Fig.
5.2
,
each rod consists of tightly packed fiber-like hexagonal carbonated HA crystals.
These HA crystallites are roughly rectangular in cross section, with a mean width of
68.3 nm and a mean thickness of 26.3 nm, and are “glued” together by a thin protein
layer less than 2 nm thick [
2
,
3
]. The interfacial area between rods is called the inter-
rod enamel, which is rich in protein and is mostly a result of the incoherence of
combining crystals of different orientations. The interrod enamel has a width of
about 1 μm. The HA crystallites in enamel rod are arranged parallel to each other
and oriented along the rod's axis [
3
,
4
]. However, the HA crystallites in the interrod
enamel are arranged with a certain inclination to the adjacent enamel rod's axis.
Since the organic matrix and water are mainly contained in interrod enamel, the
elastic modulus and hardness in the interrod enamel are lower than those in the area
of the rods. The unique microstructure endows the enamel with inhomogeneous and
anisotropic mechanical properties [
1
-
4
]. The mechanical properties, chemistry, and
microstructure of the enamel have been reported to be a function of the location in
a whole tooth [
2
].
Human tooth enamel is composed of hierarchical structures with important fea-
tures down to the nanometer or micrometer scale. Hence, a technique that can probe
the mechanical and tribological properties at these scales has the potential to address
questions that are relevant to the microscopic mechanism of tooth wear. As a pow-
erful tool for measuring the nanoscale and microscale mechanical properties of
