Biomedical Engineering Reference
In-Depth Information
21.5 Nanotechnology applications for repair and pulp regeneration
In today's studies, concerns have been raised as to the ability to transfer results from the laborato-
ries and animals in order to use what has already been developed in a confident manner. The
mechanisms of stem and progenitor cell propagation [76] , differentiation [77] and growth, types of
scaffolds [78] , neural and vascular regeneration [79] , and signaling mechanisms and the proteins
involved in signaling [80] , all without changing the genetic makeup of the tissue and without tissue
toxicity, appear to be overwhelming. In fact, the only thing that changes is the scope of the research
to deliver an environment that is able to regenerate tissue.
While human cells are larger than many of the new materials being produced at the nanoscale,
the incorporation of these materials may lead to the development and production of restorative
materials and new techniques that will close the interface completely between the margin of a tooth
preparation and the restorative material used to fill the preparation. If that occurs, microleakage of
microorganisms and other toxic substances (reinfection) will be halted and the dental pulp will be
protected with no need for treatment.
Five bonding systems were tested for microleakage using nanoparticles of silver ammoniacal
nitrate and were observed in a field emission SEM in a Yttrium aluminum garnet (YAG) backscat-
tered electron mode. Electron dispersive system analysis was carried out in parallel to identify the
existence of silver particles. Three of the restorative systems showed clear silver uptake in the
adhesive and hybrid layers [81] . A recent study examined nanostructured assemblies that would
not be toxic to pulp tissue. Melanocortin peptides (alpha-Melanocyte-stimulating hormone (MSH))
possess anti-inflammatory properties. Pulpal fibroblasts proliferation was observed in this sub-
stance which was covalently coupled with a Poly-Glutamic Acid (PGA-alpha-MSH) in the absence
of lipopolysaccharide. While the mechanisms for this effect have not been elucidated, PGA-alpha-
MSH may have important regulatory functions to modulate pulp inflammation [82] . Another study
demonstrated the use of caffeic acid phenyl ester inhibited endogenous matrix metalloproteinases
that cause hybrid layer degradation. The in vitro experiment inhibited microleakage [83] .Mine
et al. [84] found that the nanointeraction between a silorane composite (a slow shrinking, two-step
adhesive) bonded to enamel and dentin in an adhesive thickness of 10
m. A later study [85]
used a self-adhesive composite material to examine the ultrastructure between the adhesive and the
enamel/dentin. The resultant hybrid layer of a maximum of 100 nm was found. These types of stud-
ies are necessary to limit the amount of closure of root canal system space inherent to pulpal injury.
The aspect of using nanotechnological methods of measuring nano- and micromechanical prop-
erties of a biologic and mechanical tissue, such as dentin, has recently been reported. The study
was undertaken to test the zone of dentin immediately beneath the enamel
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dentin junction. The
area appears to demonstrate a softer dentin than in other areas of a tooth and is thought to play an
important role in tooth function, strain distribution, and fracture resistance. Results showed well-
known gradual increases in mechanical properties with increasing distance from the dento-enamel
junction. Control dentin showed a higher elastic modulus and hardness on the lingual side of teeth
for all measurements, while root dentin was harder on the buccal side. This suggests that nano- and
micro-mechanical properties vary with tooth side, agreeing with literature using macroscopic meth-
ods of analysis. The buccal
lingual ratios of hardness for both nano- and micromeasurements of
hardness in opposite directions in crown and root dentin suggest compensatory functions [86] .
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