Artificial Scaffolds and Mesenchymal Stem Cells for Hard Tissues - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 183

derived from the tooth buds of wisdom teeth are such a source. These cells are a
specific type of MSCs, the ectomesenchymal SCs. They are already more com-
mitted towards hard tissues since they develop from oral ectoderm and neural
crest-derived mesenchyme and form the periodontium during tooth development.
SCs from dental pulp, the dental papilla, and apical papilla progenitor cells are
another widely used source of SCs with a fairly good differentiation potential (see
[ 209 ] for a review). Thus, the tooth seems to have several different SCs with
various lineage potentials, but the limited availability nevertheless makes MSCs a
promising source [ 210 ], because they are easily accessible at nearly all times and
capable of differentiating into calcified tissue-forming cells.
Adipose tissue-derived SCs have been used in vitro to differentiate into a 3D
dental bud structure. The cells were positive for ameloblastic and odontoblastic
markers after four weeks [ 211 ]. Thetooth-specific hard tissues, enamel and dentin,
are secreted by ameloblasts and odontoblasts, respectively. However, the bud is
only the first step in tooth development, followed by the cap and bell stages, and
after the crown is complete, root formation must be initiated. Thus, there is a long
way to go before a new tooth can be grown and transplanted. Light might be shed
on the basics for the development by considering the epithelial SC niche existing
for continuously growing teeth such as in rodents, where epithelial SCs are
maintained in a cervical loop.
For defects caused by peritonitis, other difficulties must be faced. The perio-
dontium is a tissue surrounding and supporting the tooth. It is composed of
alveolar bone, which is bordered on the upper part by the connective tissue of the
gums ( the gingiva). In the lower part of the tooth, the connection of the tooth root
to the alveolar bone is via periodontal ligament and cementum. Defects in the
periodontium are therefore easily overgrown by fibroblast from the gingiva.
Collagen-based tissues can be attached to the tooth to prevent this ingrowth and
give the SCs time to fill in the gap by differentiating into the lost tissue type.
It would be beneficial to load the scaffold with bioactive molecules such as ligand
for specific P receptors to accelerate the differentiation of the ectomesenchymal
SCs [ 187 ]. Furthermore, materials for a site-specific differentiation of MSCs
within the same defect in two different lineages, such as the osteogenic and
cementogenic lineages, to form the periodontium would be favorable.
After tooth loss, the alveolar bone is quickly reduced in material due to the
lower mechanical forces on the bone. If an implant is not set in time, replacement
material for the bone is needed to stabilize the artificial tooth. For this, bone
material can be taken from the hip, but severe side effects such as infection risk,
additional pain, and reduced motility have to be considered. Artificial material
such as HA and others are an alternative, as are MSCs differentiated into bone
(see Sect. 5.1 ). If the bone itself is strong enough, there is still the question of
stabilizing the implant. For this, bone chips, a waste product derived from drilling
the hole into the bone for the implant, can be used. This material is discussed
widely among dentists, because it is in contact with the bacteria from the oral
cavity during the drilling process and it was unclear until recently whether this
material contains living cells. New data shows that this is indeed the case: the bone