87The success in the transplantation of bioengineered mature organs is whether
they can exert the immediate organ performance of its full functions in vivo (Gridelli
and Remuzzi 2000 ). In dental regenerative therapy, the most critical consideration
is whether a bioengineered tooth unit composed of mature tooth, PDL and alveolar
bone can be engrafted into the tooth-loss region, which involves natural bone
remodelling in the recipient. We have previously demonstrated the successful
engraftment of a bioengineered tooth unit with bone integration between the alveo-
lar bone of the tooth unit and that of the recipient 40 days after transplantation, and
the PDL that originated in the bioengineered tooth unit was sufficiently maintained
during the bone integration and regeneration (Oshima et al. 2011 ) (Fig. 5.5b).
Furthermore, the enamel and dentin hardness of the bioengineered tooth compo-
nents were equivalent to those of natural teeth based on the Knoop hardness test
(Ikeda et al. 2009 ; Oshima et al. 2011 ). These tooth regenerative approaches dem-
onstrated the potential for successfully restoring masticatory performance.
5.5.2 Exertion of Physiological Tooth Functions
in Bioengineered Tooth
The structural properties of periodontal tissue contribute to the physiological tooth
functions, including the absorption of occlusal loading, the maintenance of alveolar
bone height and the orthodontic tooth movement involving bone remodelling (Avery
2002 ; Fukumoto and Yamada 2005 ). Autologous tooth transplantation studies have
indicated that the remaining periodontal tissue near the tooth root could success-
fully restore physiological tooth functions including bone remodelling and the pre-
vention of ankylosis (Tsukiboshi 1993 ). By contrast, the absence of a PDL in a
dental implant is associated with deficits in essential tooth functions requiring the
coordination of the teeth and the components of the maxillofacial region through the
connection of PDL (Lindhe et al. 2008 ). Therefore, the functional cooperation
between teeth and the maxillofacial region through the biological connection of
periodontal ligament is essential for the exertion of oral functions (Avery 2002 ;
Lindhe et al. 2008 ). We have demonstrated that bioengineered teeth are able to suc-
cessfully undergo functional tooth movement equivalent to that of natural teeth
underlying the proper localisation of osteoclasts and osteoblasts in response to
mechanical stress (Ikeda et al. 2009 ; Oshima et al. 2011 ). These findings indicate
that a bioengineered tooth can replicate periodontal ligament function and lead to
the re-establishment of functional teeth within the maxillofacial region (Ikeda et al.
2009 ; Oshima et al. 2011 ).
Teeth are the peripheral organs of the sensory trigeminal and sympathetic nerves,
and the afferent nervous system in the maxillofacial region plays important roles
regarding the regulation of tooth physiological functions and the perception of nox-
ious stimuli (Luukko et al. 2005 ). It is anticipated that neuronal regeneration,
including the re-entry of nerve fibres after the transplantation of tooth germs or
5 Functional Tooth Regeneration