Biomedical Engineering Reference
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shifts from oral epithelium to the underlying mesenchyme which could
instruct tooth development when combined with non-dental epithelium
[59]. Interestingly, mesenchymal dental papilla maintains the capacity to
regenerate differentiated dental tissues including dentin, cementum and
periodontal ligament [60].
Morphologically, tooth formation starts by mapping the shape of the
crown. Then, specialized cells of dentin and enamel begin secretion of
their characteristic matrices, respectively. The size and shape of the crown
are regulated by the enamel knots that adjust growth and determine the
sites of epithelial folds which correspond directly to the cusp pattern of the
mature tooth [61]. After crown formation, the Hertwig's epithelial sheath
(HERS) maps the shape of the root. Then, secretions of radicular dentin
and cementum matrices commence together with HERS fragmentation.
This fenestrated network of epithelial cells known as epithelial cell rests
of Malassez (ERM) is the only dental epithelium that remains after tooth
eruption (Figure 6.7). Interestingly, ERM cells were isolated and induced
to proliferate, thus offering a possible source for dental epithelium stem
cell [62]. In addition, mesenchymal stem cells have been identifi ed in den-
tal pulp of human deciduous and permanent teeth as well as in the dental
follicle [63-65] . These stem cells could be cultured in vitro and differen-
tiated in vivo into odontoblasts, cementoblasts and periodontal ligament
cells, though there is no evidence that they have the capacity to participate
in tooth morphogenesis.
In conclusion, craniofacial development as well as tooth genera-
tion are induced by the appropriate cells that form tissue through their
Figure 6.7 (1) The HERS, (2) epithelial rests of Malassez, (3) dental follicle,
(4) cementoblasts, (5) periodontal ligament, (6) alveolar cells, (7) bone, and
(8) odontoblasts.
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