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of whole- tooth regeneration, the first major issue is considered to be developing a
three- dimensional cell-manipulation technology using completely dissociated epi-
thelial and mesenchymal stem cells in vitro. To date, two conventional approaches
and a novel cell-manipulation method for generating bioengineered tooth germ or a
mature tooth have been described below:
5.4.1 Biodegradable Scaffold Method
Conventional scaffold technology represented by three-dimensional tissue engi-
neering has contributed to the large-scale tissue regeneration through seeding stem/
progenitor cells on the degradable materials such as natural molecules and synthetic
polymers. This method has been proven a high utility in three-dimensional tissue
engineering technology, and these preparations have been used in clinical applica-
tions including bone and cartilage regenerative therapies (Quarto et al. 2001 ; Cao
et al. 1997 ; Caplan and Bruder 2001 ). Previous studies using collagen/gelatine
sponges or polyglycolic acid/poly-L-lactate-co-glycolide copolymers (PLA/PLGA)
have reported the partial generation of tooth-tissue structure including enamel, den-
tin and dental pulp, through seeding epithelial and mesenchymal cells isolated from
porcine tooth germ (Honda et al. 2003 ; Young et al. 2002 ; Iwatsuki et al. 2006 ;
Duailibi et al. 2004 ; Yelick and Vacanti 2006 ; Sumita et al. 2006 ; Honda et al. 2007 ;
Ohara et al. 2010 ). Although scaffold-based technology may be practical for con-
trolling tooth shape and size, the fundamental problems regarding the regeneration
of whole-tooth itself have not been resolved. The presence of residual scaffold
material after in vivo transplantation is considered to be the cause of the low
frequency of tooth formation and the irregularity of the resulting tooth-tissue
structures, e.g. the enamel-dentin complex due to the orderly cell arrangement of
ameloblast/odontoblast lineages (Honda et al. 2003 ; Young et al. 2002 ). Fully
regeneration of proper tooth structure using scaffolds requires the formation of
complex junctions between the enamel, dentin and cementum that result from accu-
rate spatiotemporal cell gradients of ameloblasts, odontoblasts and cementoblasts as
well as natural tooth development (Volponi et al. 2010 ; Nakao et al. 2007 ).
5.4.2 Cell Aggregation Method
The cell aggregation method is known as a typical bioengineering protocol employed
for the reconstitution of a bioengineered organ germ to reproduce the epithelial-
mesenchymal interactions that occur during organogenesis (Volponi et al. 2010 ).
Previous studies have reported that transplanting bioengineered cell aggregates
derived from the ectodermal organs such as hair follicle and mammary gland and
demonstrated the regeneration of each reconstructed organ with the proper tissue
structure and cellular arrangements (Zheng et al. 2005 ; Shackleton et al. 2006 ).
M. Oshima and T. Tsuji