Biomedical Engineering Reference
In-Depth Information
Dentin as a biologic and mechanical tissue was thought to be more prone to brittleness if the dentin
surrounding the pulp canal space had been exposed to the stress of cleaning and shaping, and to the
use of irrigants, sealers, and core materials
[87]
. In a recent study Cheron et al.
[88]
found that
while not knowing what irrigants were used in the endodontic techniques, patient (tooth) age may
be correlated to higher fracture susceptibility. A nanoscope atomic force microscope (AFM) with
a triboscope head used with a Bercovich diamond tip was used in the experiment
[89,90]
.
Interestingly, results of the Cheron et al. study
[88]
demonstrated that there was no difference in
the modulus of elasticity or hardness of radicular intertubular dentin when comparing root-treated
dentin (root canal procedure) with normal root dentin. The use of the AFM was very helpful in the
concluding that treated dentin appeared to be the same.
As previously stated, research into the use of nanotechnology in various phases of the repair
and regeneration of the dental pulp has not frequently been seen. However, several papers have
theorized as to where the technology must move. While theoretical, there has been movement to
begin such studies. Kanaparthy and Kanaparthy
[91]
and Freitas
[92]
have speculated that nanoro-
bots could be constructed from parts with dimensions in the range of 1
100 nm. This may allow
the co-use of substances as nanosensors for the delivery of precise amounts of a therapeutic
agents used with pulp capping materials and drugs, such as antibiotics, as previously proposed.
There was great hope that new systems of dental restorative materials using nanoparticles would
also be developed.
The hard tissue directly below enamel is dentin. Dentin has a tubular structure formed by pulp
cells, the odontoblasts. The dentin tubules contain an arm-like soft tissue extension, the odontoblast
process, and fluid composed mainly of various proteins. Pulp sensory neurons are found and may
extend into the tubules some distance around the odontoblast process
[93]
. The odontoblast and its
process is the principal cell that is responsible for formation of the dentin matrix, which itself
mineralizes into two types of dentin. Primary dentin matrix is initiated once the dental pulp cells
and other cells involved in enamel formation are completed embryonically. Mineralization occurs
throughout the crown and roots to complete tooth formation. Each odontoblast is an end-stage cell
that remains functional over the entire lifetime of the pulp, unless replaced by an odontoblast-like
cell during infection or injury. Secondary dentin forms throughout the life of the tooth through the
same mechanisms and same cells that produced primary dentin and is a normal physiologic process.
Both dentins are tubular with the tubules of secondary dentin being roughly a continuation of the
tubules of primary dentin
[94]
. The formation of secondary dentin is at the expense of the root
canal space and its contents. Therefore, since it is physiologic, the eventual result, if one lives long
enough, is to see a marked narrowing and shortening of the canal space. A third type of dentin also
is formed, which is the tertiary dentin. It is formed in response to trauma, injury, or infection and
is atubular. While also protective in the first instance, it narrows the pulp space and is sometimes
spoken of as a pathologic process. In an unchecked carious lesion, when microorganisms or toxins
enter the pulp space and tissue, odontoblasts in the area of inflammation and infection are killed.
Repair and regeneration may be possible through several therapies that are available and studies to
date indicate formation of an odontoblast-like cell in place of the original odontoblast. The result-
ing tertiary dentin is formed with an atubular structure
[95]
. This explanation is necessary to under-
stand the role of nanotechnology in repair and regeneration since these processes are not the same
as the embryologic processes that formed the tooth originally.
