at the cusps, thinning to a knife edge at the
cervical line. It is formed only once and cannot
regenerate or repair itself. Thus, when enamel is
destroyed by decay, operative dentistry is required
to reconstruct the tooth. Enamel has no nerve
fibers and cannot register sensations.
. Dentin is the light yellow substance that
makes up the bulk of the tooth. It is softer than
enamel but harder than bone and is located
inside the crown under the enamel. The point at
which the dentin and the enamel meet is called
the dentinoenamel junction. Dentin is also found
inside the root of the tooth under the cementum.
The inner surfaces of the dentin forms a
hard-walled cavity that contains and protects the
Unlike enamel, dentin continues to form
throughout the life of the tooth. When the
dental pulp is mildly stimulated as a result of
caries, cavity preparation, abrasion, attrition, or
erosion, a protective layer of secondary dentin is
formed on the pulp wall.
Even though dentin is not sensitive to stimuli,
sensation may result when mechanical, thermal,
or chemical stimuli are applied to it. The
sensation comes not from the dentin itself but
from cells that extend into it. These cells are
actually part of the pulp, not the dentin, and they
are sensitive to stimuli.
l Cementum is a bonelike substance,
although it is not as hard as bone. It forms a pro-
tective layer over the root portion of the dentin.
The cementum joins the enamel at the cervix of
The main function of cementum is to anchor
the tooth to the socket by attaching to the
principle fibers of the periodontal ligament.
Cementum is formed continuously throughout
the life of the tooth. Thus, it compensates for the
loss of tooth substance due to wear by attaching
new fibers of the periodontal ligament to the root.
l Pulp is soft tissue that fills the pulp
cavity. This tissue contains numerous blood
vessels and nerves that enter the tooth through
the apical foramen. It is enclosed within the hard,
unyielding dentin walls of the pulp cavity. The
cavity has two parts: the pulp chamber and the
root, or pulp canal. The chamber is located
inside the crown. The canal is located inside the
An important function of the pulp is to form
dentin. It provides the cells from which dentin is
formed and supplies the dentin with blood.
Pulp responds to external stimuli, providing
sensation to the tooth. It responds to irritation
either by forming secondary dentin or by
becoming inflamed. Since the walls of the pulp
chamber and root canal permit no expansion of
the pulp tissue, any inflammatory swelling of the
tissue will compress the blood vessels against the
walls. This results in a condition known as
hyperemic pulp, which can lead to necrosis of the
Tissues of the Periodontium
The tissues that surround and support the
teeth are the cementum, the alveolar process,
the periodontal ligament, and the gingivae.
Collectively, these tissues are known as the
periodontium. Throughout the following dis-
cussion, refer to figure 2-5.
. The alveolar process is the portion of the
maxillae and mandible that forms and supports
the sockets (alveoli) of the teeth.
The alveolar process can be divided into two
parts: the alveolar bone proper and [he supporting
alveolar bone. The alveolar bone proper is a thin
layer of bone that lines the tooth socket and
attaches the principal fibers of the periodontal
ligament. The supporting alveolar bone is the
portion of the alveolar process that surrounds the
alveolar bone proper and gives support to the
l The periodontal ligament consists of
hundreds of tissue fibers that, except at the apical
foramen, completely surround the tooth root. The
ligament acts as a shock absorber, reducing the
impact of the teeth as they occlude.
l The gingivae are the soft tissues that cover
the alveolar process and surround the necks
of the teeth. They consist of an outer layer
of epitheliums and an inner layer of connective
Healthy gingivae are pink, firm, and resilient.
They have a stippled appearance. Stippling refers
to the orange peel texture of the healthy tissue.
Inflammation causes a loss of stippling. When
inflamed, the gingivae may become sore and
swollen, and they may bleed.