c. Gingival Tissue and the Crown. In young persons, part of the enamel of a
tooth is normally covered by gingival (gum) tissue. Only the clinical crown is exposed.
On older persons, it is common for the tooth's enamel to be completely exposed above
the gingiva (the anatomical crown) and even to have part of the root surface showing.
TISSUES OF THE TEETH
a. Enamel. Enamel is the calcified substance that covers the entire crown of
the tooth. It consists of approximately 96 percent inorganic (nonliving) material and it is
the hardest tissue in the human body. Enamel is thickest at the top of the teeth (at the
cusps), thinning to a knife edge thickness where the crown and root join (the cervical
line). Enamel 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. It is strong and hard. It
has the ability to withstand the stress of mastication and does not wear away easily. It
is thick in areas that contact opposing teeth. Enamel serves to protect the underlying
softer dentin. The color of a tooth is derived from the enamel, which is usually shaded
from light yellow to white.
b. Dentin. The bulk of the tooth is made up of a calcified tissue called dentin.
Dentin is a light yellow substance that is softer than enamel but harder than bone. It
consists of approximately 65 percent inorganic matter. It is slightly elastic and
compressible. Dentin is found inside the crown under the enamel. Dentin is also found
inside the root of the tooth under the cementum. The inner surface of the dentin forms
a hard-walled cavity that contains and protects the pulp. Unlike enamel, dentin
continues to form throughout the life of the tooth.
c. Cementum. Cementum forms a protective layer over the root portion of the
dentin. It consists of 50 percent inorganic material and is a bonelike substance,
although it is not as hard as bone. The cementum joins the enamel at the cervix (neck)
of the tooth. The point at which they join is called the cementoenamel junction. The
main function of cementum is to anchor the tooth to the socket by providing attachment
for the principal fibers of the periodontal ligament. Cementum is formed continuously
throughout the life of the tooth.
d. Pulp. The pulp is the soft tissue that fills the pulp cavity. This tissue contains
numerous blood vessels and nerves which enter the tooth through the apical foramen.
The pulp is enclosed within the hard, unyielding dentin walls of the pulp cavity. The pulp
cavity has two parts: the pulp chamber and the root canal (or pulp canal). The pulp
chamber is located inside the crown. The root canal (or pulp canal) is located inside the
root. An important function of the pulp is the formation of dentin. Pulp responds to
external stimuli, providing sensation to the tooth. Any inflammatory swelling of the pulp
tissue will compress the blood vessels against the walls. This condition can lead to
death of the pulp tissue.