Biomedical Engineering Reference
In-Depth Information
the material, changing strain values are necessary during the course of the test. A spherical tipped
indenter can be used to meet this need
[72]
. Equivalence exists between conventional stress-strain
curves and those generated by plotting hardness versus
a
/
R
, contact radius,
a
, divided by indenter
radius,
R
, when using a spherical tipped indenter. The depth of indenter in contact with the material,
h
p
, can be determined using the Oliver-Pharr method as
h
p
h
t
0.75(
P
t
/
S
), where
h
t
and
P
t
are the
peak displacement and load at the onset of unloading.
In order to provide materials for dental crown/bridges that are structurally reliable, strong and
tough with primarily an elastic response, materials such as toughened ceramics are required
[73]
.
On the other hand, materials with too high a hardness or yield response may damage opposing teeth
during occlusal contact. A nano-based indentation system (Ultra Micro-Indentation System, UMIS-
2000, CSIRO, Australia) was used to determine the indentation stress-strain response of two kinds
of dental ceramics (Cerec
®
2 Mark II, Sirona Dental Systems, New York, USA; and Vita VM9, VITA
Zahnfabrik H. Rauter Gmbh & Co. KG, Germany), one kind of dental alloy (Wiron® 99, Bego
Bremer Goldschlagerei Wilh. Herbst Gmbh & Co, Bremen, Germany) and healthy enamel
[73]
. A
spherical indenter was used to test the materials with nanometer and micronewton displacement and
force resolution. Assuming that the elastic modulus remained constant, a plot of contact pressure ver-
sus contact strain,
H
-
a
/
R
, of each material was obtained. It was concluded in this work that only the
metallic alloy (stiffness of approximately 2 GPa) had similar stress-strain response to enamel. Dental
ceramics showed much higher yield stress (Mark II and VM9 approximately 10 and 7 GPa, respec-
tively) response than enamel. From this work,
H
-
a
/
R
curves can be seen to provide a method to com-
pare the mechanical properties of these different dental materials.
18.5
CONCLUSIONS
Nanotechnology has, and will in the future have, a large impact on technology development for devel-
oping dental materials and systems. Some of these include drug delivery systems, structural materi-
als, biochemical and biomedical devices, adhesives, and pigments. In recent years, with the advent of
many new techniques to fabricate nanostructures and their potential applications, the tools to be able
to characterize nanoscale systems are becoming more commonly used and increasingly required as
standard research tools. In this chapter, methods to characterize to the micron, nano- and angstrom
scale of topology and internal structure were discussed. Images captured for internal structure or sur-
face topography mapping are often processed with software techniques to extract better resolution
and further information from the captured data. Image processing and quantitative morphological
measurements are therefore important areas for research to allow the most to be made of these often
expensive and time-consuming characterization techniques. Applications and reviews of this software
research by which nanoparticles can be characterized have been published
[74-76]
.
Methods of chemical characterization of these structures down to 100 ppm were presented in this
chapter. Two other spectroscopy techniques worth mentioning are Raman spectroscopy and Fourier-
transform infrared (FTIR) spectroscopy. Raman spectroscopy is commonly used to detect specific
molecular bonds. For this technique, the sample to be analyzed is generally illuminated laser light
with frequency within the visible, infrared, or ultraviolet ranges. Reflected light is focused through
a monochromator filtering out wavelengths close to the laser wavelength to allow the detection of
other scattered wavelengths. A very small percentage of scattered photons are scattered by excitation
