anatomical crown are frequently buried in gingival
enamel may be attributed to the variation in the
tissue. As a person gets older, it becomes common for
a tooths enamel to be completely exposed above the
gingiva and to have root surface showing (gingival
recession). The term clinical crown is applied to the
part of the crown exposed (visible) in the mouth.
thickness, translucent proprieties, and the quality of
the crystal structure and surface stains of enamel.
Enamel (fig. 4-6) is the calcified substance that
covers the entire anatomic crown of the tooth and
protects the dentin. It is the hardest tissue in the human
body and consists of approximately 96% inorganic
The root of a tooth is embedded in alveolar bone
and is covered by cementurn. The tooth may have a
single root or it may have two or three roots. When
teeth have more than one root, the region where the
roots separate is called the furcation. When a tooth has
two roots, the root portion is said to be bifurcated.
When it has three roots, the root portion is said to be
trifurcated (fig. 4-5). If a tooth has four or more roots,
it is said to be multirooted. The tip of each root is called
apex. On the apex of each root, there is a small opening
that allows for the passage of blood vessels and nerves
into the tooth. This opening is called the apical
The cervix or cervical line (fig. 4-4) is a slight
indentation that encircles the tooth and marks the
junction of the crown with the root. The cementum
joins the enamel at the cervix of the tooth. The point at
which they join is called the cementoenamel junction
or cervical line.
minerals, 1% organic materials, and 3% water.
Calcium and phosphorus (as hydroxyapatite) are its
main inorganic components. Enamel can endure
crushing pressure of approximately 100,000 pounds
per square inch. A layering of the dentin and
periodontium, coupled with the hardness of the
enamel, produces a cushioning effect of the tooths
different structures enabling it to endure the pressures
of mastication. Structurally, enamel is composed of
millions of enamel rods or prisms. Each rod begins at
the dentinoenamel junction (junction between the
enamel and dentin) and extends to the outer surface of
the crown. Enamel is formed by epithelial cells
(ameloblasts) that lose their functional ability when
the crown of the tooth has been completed. Therefore,
enamel, after formation, has no power of further
growth or repair.
Dentin (fig. 4-6) is the light yellow substance that
is more radiolucent than enamel and is very porous; it
constitutes the largest portion of the tooth. The pulp
chamber is located on the internal surface of the dentin
walls. Dentin is harder than bone but softer than
enamel. Dentin consists of approximately 70%
inorganic matter and 30% organic matter and water.
Calcium and phosphorus are its chief inorganic
TISSUES OF THE TEETH
This section describes the histologic structures of
enamel, dentin, cementum, and the dental pulp. Figure
4-6 illustrates the tissues of the teeth.
Enamel is translucent and can vary in color from
yellowish to grayish white. The different colors of
Figure 4-5.Bifurcated and trifurcated roots.
Dentin is a living tissue and must be protected
during operative or prosthetic procedures from
dehydration (drying) and thermal shock. The dentin is
perforated by tubules (similar to tiny straws) that run
between the cementoenamel junction and the pulp.
Cell processes from the pulp reach part way into the
tubules like fingers. These cell processes create new
dentin and mineralize it. Dentin transmits pain stimuli
by the way of dentinal fibers. Because dentin is a
living tissue, it has the ability for constant growth and
repair that reacts to physiologic (functional) and
pathologic (disease) stimuli.