Following a pulp exposure, gradual alterations dues to the
carious decay were detected in the dental pulp. Small necrotic
foci exhibiting limited necrosis were noticeable, and they
were growing slowly or rapidly. A sequence of treatment of
the infected pulp leads endodontic therapy. Elimination of
the infection and the protection of a decontaminated tooth,
free from future microbial invasion, implicate the removal of
nerve, blood vessels, cell remnants and fibers containing connective
tissue. They contribute to direct the shaping, orientation,
and enlargement of the root canal, while cleaning of
the roots. This is completed by the filling of decontaminated
canals with a stable material. Since more than one century,
root canal treatments provide good results in the context of
endodontic therapies. It was clearly shown that as a consequence
of endodontic therapy, pulp healing and regeneration
were stimulated inside the root canal. This possibility was
linked to the survival of some pulp cells, despite severe pulp
alterations.
Inflammatory and immune reactions combine with pulp destruction.
The pulp contains cells reacting positively to the
carious attack. Inflammatory cells have been characterized.
They include dendritic cells, histiocytes/macrophages, T lymphocytes
and latent stem cells (progenitors), involved in the
stem cells self-renewal.
Anti-inflammatory agents include
also a series of mediators such as steroids, interleukin-I receptor
antagonist, solid tumor necrosis factor (TNF) receptor,
IL-10, nitric oxide (NO), heme oxygenase-1 and regulatory Tlymphocytes
(Tregs). They play a crucial role by limiting tissue
damages. Programmed cell death involves necrosis, apoptosis,
nemosis, pyroptosis and autophagy. Proteases are also associated
to such processes. They implicate caspases, calpains,
cathepsins and transglutaminases. Obviously, reparative dentinogenesis
is associated to the expression of class II MHC
markers located at the surface of macrophages. These cell
markers are involved in the recovery of the wounded root canal,
a prerequisite for pulp rescue, leading ultimately to pulp
regeneration.
Embryonic stem cells (ECSs) and induced pluripotent cell lines
(IPs) provide different tools with a potential for regeneration.
However, their phenotype is unstable and the initial phenotype
is ultimately restored. In adult teeth, there are a small
number of stem cells compared with the total of pulp fibroblasts
or pulpoblasts, according to Baume analysis.
After
isolation, expansion, and characterization of the multipotent
human mesenchymal stem cells, 5 to 7 days after the initial
plating, committed progenitor cells display a restricted potential.
Evaluated by Pittenger et al. as being about 0.001 to
0.01% of the grand total of cells, the subset of undifferentiated
cells represents in the dental pulp as little as 1% of the
total cell population according to Sloan and Waddington.
Side population (SP) cells in human deciduous dental pulp
were evaluated to be 2% of the total cells. According to
Kenmotsu et al. approximately 0.40% of the pulp cells may
be stem cells or side population when they are found in young
rats, whereas only 0.11% is found in old rats.
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