CHAPTER 4
ORAL ANATOMY
This chapter covers the oral anatomy and
physiology of the teeth, the histology of their tissues
and supporting structures, and concentrates on the
external features of the teeth. To understand the
material in this section, you must become familiar with
the terms used to describe the external features of the
teeth. In addition, you must know the numbering
system by which the teeth are identified on the
standard dental chart used by the armed services. As a
basic dental assistant, you must be aware that teeth
differ in size, shape, and other characteristics from one
person to another. Such knowledge will be useful to
you when you fill in dental charts, expose radiographs,
clean teeth, and assist in all phases of dentistry
throughout your career.
FORMATION PERIOD
As all living things are forming, they go through a
developmental process to reach maturity or a final
outcome. When teeth are in the odontogenesis phase
(tooth formation), every tooth goes through three
developmental processes. They are categorized into
the growth, calcification, and eruption periods
(illustrated in figure 4-1). The term emergence is used
to describe the tooth as it is breaking through the
gingival tissue.
GROWTH PERIOD
Dental development usually begins in the fifth or
sixth week of prenatal life. By the seventh week, skin
cells of the mouth called epithelium thicken along the
ridge of the developing jaws creating a horse-shoe
shaped band called the dental lamina. The growth
period of development is divided into the bud, cap, and
bell stages.
Bud Stage
From the dental lamina, patches of epithelial cells
grow into the underlying tissues. These patches of cells
are called tooth buds. As soon as the dental lamina is
formed, the tooth buds for the primary teeth develop.
Usually 10 tooth buds are present in each dental arch
and they give rise to future primary teeth. Tooth buds
for the permanent teeth form between the 17th week
of fetal life through the age of 5 years. When the
primary teeth are lost, permanent teeth will replace
them.
Cap Stage
This stage is also known as proliferation
(reproduction or multiplication) in which the cells of
the tooth grow and the tooth bud takes a hollowed
caplike shape. The epithelium of the cap will give rise
to the enamel. The zone under the cap is called the
dental papilla. The dental papilla gives rise to the
dentin, cementum, and the pulp.
Bell Stage
The last period of growth is also known as
histodifferentiation (the acquisit on of tissue
characteristics by cell groups) or bell stage. It is here
the ameloblast cells form the enamel, odontoblast cells
form the dentin, and the cementoblast cells form the
cementum.
MORPHODIFFERENTIATION
As the tooth is in the bell stage, it begins to take
shape and form through a process called mor-
phodifferentiation. Enamel forming cells (ameloblast)
and dentin forming cells (odontoblast) line up on a
boundary line called dentinoenamel junction.
APPOSITION
Apposition refers to the depositing of the matrix
for the hard dental structures. This matrix is deposited
by cells along the boundary line at the end of
morphodifferentiation.
CALCIFICATION
Calcification (fig. 4-1) is the process by which
organic tissue (the matrix formed during apposition)
becomes hardened by a deposit of calcium or any
mineral salts. Next, the tooth crown receives layers of
enamel that start at the top of the crown and go
downward over the sides to the cementonenamel
junction.
4-1
