Biomedical Engineering Reference
In-Depth Information
The second structural component of the enamel matrix is the
interrod (or interprismatic) enamel, which surrounds and packs
between the rods. The difference between the rod and the interrod
is the orientation of apatite crystals; the rod contains aligned
crystallites, whereas the mineral in the interrod is less ordered.
These structures coalesce to form the tough tissue of enamel, which
can withstand high forces and resist damage by crack deflection.
The third structure, aprismatic enamel, refers to the structures
containing apatite crystals that show no mesoscale or macroscale
alignment [533]. Enamel is a selectively permeable membrane,
allowing water and certain ions to pass via osmosis [676, 677].
formation and development of teeth appears to be
even more complicated when compared with the afore-described
process of bone formation. It is a very complex biological process, by
which teeth are formed from embryonic cells, grow and erupt into
the mouth [578]. For human teeth enamel, dentine and cementum
must all be developed during the appropriate stages of fetal
development. Primary (baby) teeth start to form between the sixth
and eighth weeks
The
in vivo
in utero
, while the permanent teeth begin to form
in the twentieth week
[676, 677]. recent data confirmed the
necessity of calcium orthophosphates in the diet of pregnant and
nursing mother to prevent early childhood dental caries [700].
As teeth consist of at least two materials with different properties
(enamel and dentine), the tooth bud (sometimes called “the tooth
germ” — that is an aggregation of cells that eventually forms a tooth)
is organized into three parts: the enamel organ, the dental papilla
and the dental follicle. The enamel organ is composed of at least four
other groups of cells (for the biological details see Refs. [676, 677]).
Altogether, these groups of cells give rise to ameloblasts, which secret
enamel matrix proteins. The protein gel adjacent to ameloblasts
is supersaturated with calcium orthophosphates, which leads to
the precipitation of biological apatite. Similarly, the dental papilla
contains cells that develop into odontoblasts, which are dentine-
forming cells. The dental follicle gives rise to three important entities:
cementoblasts, osteoblasts, and fibroblasts. Cementoblasts form the
cementum of a tooth [682]. Osteoblasts give rise to the alveolar bone
around the roots of teeth (see bone formation above). Fibroblasts
develop the periodontal ligaments that connect teeth to the alveolar
bone through cementum [576-578, 676, 677].
in utero
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