Biomedical Engineering Reference
In-Depth Information
(A)
(B)
Re
1
2
A
HL
1
2
1
4
5
D
3
4
10
ยต
m
FIGURE 7.22
Nanoindentation along composite, adhesive layer, hybrid layer, and dentin for nanoscale mechanical
evaluation of the adhesive junction.
dentin having the same morphology as those shown by field-emission SEM, but without the need
for coating or sample preparation. Another important AFM study on collagen collapse due to dehy-
dration was conducted by Fawzy
[48]
where he showed that the ability of the demineralized dentin
collagen network to resist air dehydration and to preserve the integrity of open network structure
with the increase in air exposure time is increased with dentin depth (
Figure 7.21
).
Another important aspect of AFM as a research tool in the field of adhesion is nanoindentation
(
Figure 7.22
) to evaluate mechanical properties of adhesive junctions and hybrid layers
[49]
.
Sauro et al.
[50]
studied the quality of resin dentin interfaces using AFM nanoindentation and
they found that a HEMA-containing adhesive applied onto phosphoric acid etched ethanol or water-
wet dentin created hybrid layers with the lowest biomechanical nanoproperties. Nanoindentation
allows the investigation of selected material properties on small amounts of materials, based on the
load-displacement data of indentations on a submicron scale. Measurement of mechanical properties
by nanoindentation has been suggested as advantageous over the conventional methods for its high
resolution of force and accurate indent positioning
[51
53]
. This method has been used to measure
the elastic modulus and hardness of the dental adhesives by some researchers
[51,52,54]
.
7.8
How can nanoscience and nanotechnology improve the outcome of
clinical adhesive dentistry?
Based on nanoleakage data and extensive research on the degradation of the adhesive bonds, the
following approaches seem to be promising in the field of clinical adhesive dentistry.
7.8.1
Use of hydrophobic coating
Since the incorporation of hydrophilic monomer blends in simplified adhesives (two-step etch-and-
rinse and one-step self-etch adhesives) dramatically reduced bond longevity, the need of a hydro-
phobic coating with a not-solvated bonding layer seems to be pivotal to reduce water sorption and
