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Tooth root formation is initiated after tooth crown formation, and the mature teeth
erupt into the oral cavity (Avery 2002 ; Nanci 2012 ). In mature tooth, after tooth
development, immature cells seem to be maintained as adult tissue stem cells that
are thought to act as a self-repair system for dental tissues and supply a wide variety
of each dental cell type after the dental tissue injury (Egusa et al. 2012 ) (Fig. 5.1).
5.3 Tissue Repair and Engineering by Using Dental Tissue-
Derived Stem Cells and Cytokines
Tissue-derived stem cells, including haematopoietic stem cells, neural stem cells,
skin stem cells and mesenchymal stem cells, allow for self-renewal and differentia-
tion to maintain homeostasis and to repair injured tissues. Recent studies of stem/
progenitor cells have provided new insights that have furthered our understanding
Fig. 5.1 Schematic diagram of tooth development. The oral epithelium elongates into the mesen-
chymal tissue region, and then a tooth bud is formed by the condensation of neural crest-derived
mesenchymal tissue (ED11–13). The first enamel knot, which acts as a signalling centre to orches-
trate tooth development by controlling the gene expression of various signalling molecules and
transcription factors, appears in the dental epithelium (ED13–15). The secondary enamel knots are
generated; these regions play an important role in regulating the position and number of tooth
cusps (ED16–17). The epithelial and mesenchymal cells in the tooth germ terminally differentiate
into the tooth tissue-forming cells such as ameloblasts and odontoblasts, respectively. These cells
secrete a collagenous extracellular matrix to mineralise into the enamel or dentin matrix at the
interface between epithelium and mesenchyme (ED18–newborn). In the same period, the outer
mesenchymal cells around tooth germ form the dental follicle tissue that can generate periodontal
tissue including cementum, periodontal ligaments and alveolar bone. Tooth root formation is initi-
ated after tooth crown formation, and the mature teeth erupt into the oral cavity
M. Oshima and T. Tsuji