Biomedical Engineering Reference
In-Depth Information
region may be another site for silver uptake. Although the amount of nanoleakage may be very small
(nanometer size) in the bonded assembly, it has the potential to serve as a pathway for water move-
ment within the adhesive
dentin interface over time. The water movement within the adhesive
dentin interface may extract unconverted monomers from resin adhesive or hybrid layer which
contributes to reductions of bond strength
[41]
. Therefore, the effect of nanoleakage on the bond
strength, and on the integrity of resin
dentin bonds has gained importance not only for short-term,
but especially for long-term adhesion. Evaluation of silver uptake (i.e. nanoleakage evaluation) pro-
vides good spatial resolution of submicron defects in resin infiltration or inadequate polymerization.
Nanometer-sized spaces within resin
dentin interfaces, evidenced by the nanoleakage technique,
might be large enough for enzymes to enter
[42]
. It is currently believed that exposed collagen fibrils
in resin
dentin interfaces might be digested by host-derived matrix metalloproteinases (MMPs)
[43]
.
MMPs were identified in either nonmineralized or mineralized compartments of human dentin
matrices. MMPs belong to a group of zinc- and calcium-dependent enzymes that have been shown
to be able to cleave native collagenous tissues at neutral pH in the metabolism of all connective tis-
sues. Dentin matrix has shown to contain at least four MMPs: the stromelysin-1 (MMP-3), the true
collagenase (MMP-8), and the gelatinases A and B (MMP-2 and MMP-9, respectively). These
host-derived proteases are thought to play an important role in numerous physiological and patho-
logical processes occurring in dentin, including the degradation of collagen fibrils that are exposed
by suboptimally infiltrated dental adhesive systems after acid etching
[44]
.
7.7
Atomic force microscopy in the field of dental adhesion
Atomic force microscopy (AFM) is one of the most important tools in the field of nanoscience and
nanotechnology. AFM could be used for the study of microstructure of dental substrates and can
supply valuable data in this field. It could also be used in the field of characterization of resin tooth
bonds by studying nanoscale mechanical properties of the dental adhesive junctions so that the
quality of hybrid layers could be assessed in terms of its elastic modulus and hardness by nano-
indentation. Many research tools were used to investigate microstructure of hard dental substrates.
These tools included SEM and TEM. Extensive sample preparation and coating for SEM or TEM
technique arises the problem of viewing and imaging samples in their natural conditions. On the
contrary to SEM and TEM, scanning probe microscopes and, in particular, AFM has facilitated the
imaging and analysis of biological surfaces with little or no sample preparation. AFM can operate
in air or in liquid, and the imaging of macromolecules like proteins or DNA has been reported by
several authors
[45]
. AFM could be used to investigate the effect of conditioner on dentin morphol-
ogy and structure, giving clinicians more knowledge and better understanding of the adhesion pro-
cedure and problems associated with it.
Dentin collagen fibrils were studied in situ by AFM (
Figure 7.20
). New data on size distribution
and the axial repeat distance of hydrated and dehydrated collagen type-I fibrils are presented
[46]
.
This method provides additional insight into the structure and organization of dentin collagen and
may contribute to a better understanding of alterations in collagen structure induced by chemical or
biochemical treatments, age, or diseases. Modeling of the fibril structure using these data is encour-
aged to better understand the effect of dehydration on the molecular level
[46]
.
