Biology Reference
In-Depth Information
are still present. See Hammerl (Chapter 10), this volume, for more information on episodes of
stress recorded by enamel.
Dentin
The bulk of the tooth is made of dentin. Dentin, like bone and enamel, is also a calcified
tissue. In fact, dentin is harder than bone but not as hard as enamel (
Junqueira and Carneiro,
2003
). Dentin is formed by specialized cells called odontoblasts, which are derivatives of
embryologic neural crest cells. The odontoblasts are polarized cells that travel from the
internal border of the enamel towards the area that will become the pulp cavity; they secrete
an organic matrix called predentin. As the odontoblasts secrete predentin they leave their long
apical extensions called odontoblast processes trailing behind them. These slender cellular
extensions reside in hollow tubules located throughout the dentin, called dentinal tubules.
These tubules contain the protoplasmic extension of the odontoblast cells lining the pulp
chamber and provide a link between enamel and the pulp organ. The tubules may contain
nerve, vascular and lymphoid tissues from the pulp organ.
Once secreted, the predentin begins the mineralization process, which is controlled by
another part of the odontoblasts called the matrix vesicles, which cause the hydroxyapatite
crystals to grow and harden. Unlike enamel, dentin is sensitive to outside factors such as
temperature, trauma, and acidic pH (
Junqueira and Carneiro, 2003
). Any stimuli to the
dentin are interpreted as the sensation of pain.
Cementum
Cementum covers the outside of the root, and is very similar to bone but without any
blood or nerve innervations and without the Haversian systems seen in bone (
Junqueira
and Carneiro, 2003
). The layer of cementum functions to attach the root of the tooth to the
periodontal ligament, which helps to provide critical stabilization of the tooth in the bone
of either the mandible or maxilla. The cementum primarily covers the root, with some
portion overlapping the crown. The cementum is made by specialized mesenchymal cells
located on the outside of the tooth root. Once these cells come into contact with the dentin
that has just been made, some differentiate and turn into cementoblasts (
Sadler, 2006
). Once
these cells become trapped within the matrix of the cementum, they live on as cementocytes.
Like osteocytes in bone, cementocytes are reactive cells and can secrete cementum to help
keep the tooth stable within the socket (
Junqueira and Carneiro, 2003
).
Pulp Cavity
The pulp cavity is a space on the interior of the tooth that is filled with cellular material
and soft tissue. The pulp cavity has two areas, each defined by location. The pulp chamber
is the area of the pulp cavity that is located within the crown portion of the tooth, and the
root canal is the hollow portion located within the root of the tooth (
Junqueira and Carneiro,
2003
). The root canal extends all the way down the root of the tooth, where it exits the tooth
through the apical foramen. The apical foramen allows for the entrance and exit of nerves,
lymphatic tissues, and blood vessels to the living cells of the tooth.
The pulp inside the pulp cavity is a highly innervated and vascular tissue. The cells inside
the pulp cavity are mainly loose connective tissue, fibroblasts, and odontoblasts, and ground
substance. The nerve cells within the pulp only respond to the sensation of pain.
