development and their growth are influenced by several predisposing
factors. Among these factors, genetics constitute a large part
of the individual’s teeth development and growth.
Growth and eruption of teeth in the mouth is caused by numerous,
complex series of gene expressions that result in teeth formation
that came from embryonic cells.
The ectomesenchyme is an embryonic connective tissue that is
covered by one to two layers of thick epithelium. These are the
cells that lines that newly formed primitive mouth. Development
of teeth starts when the embryonic epithelial and the neural
crest that arises from mesenchymal cells starts to interact with
Later, a continuous band of thick epithelium forms around this
primitive mouth, which would become the jaws after about 37 days.
From each of these epithelium bands, the dental and vestibular
lamina is quickly formed. Sites of the future teeth inside the
dental lamina, which has every series of epithelial outgrowths
into the mesenchyme are formed. After this, tooth development
proceeds in three stages. These are the bud, cap, and bell.
1. Bud stage – This stage is represented by the multiplication
of the epithelium into the ectomesenchyme of the jaw. These supporting
ectomesenchymal cells are packed closely beneath and around the
2. Bud to Cap – This transition from bud to cap is represented
by the onset of differences between tooth germs. This will later
give rise to different teeth.
3. Cap stage – This stage undergoes a condensation of
the ectomesenchyme. This condensation is the multiplication of
the tooth bud into the ectomesenchyme that in turn increases
the density of the adjacent epithelial outgrowth by the dental
lamina. The lateral lamina results as the bud becomes larger,
it drags along and tethers itself to the dental lamina. Formative
elements of the tooth and its supporting tissues are now identified
in this stage.
The epithelial outgrowth resembles a cap, hence the name. This
cap sits on a ball of condensed ectomesenchyme cells, which are
called the enamel organ. This enamel organ will become the tooth
enamel, while the ectomesenchyme cells or dental papilla will
become the dentin and the pulp. The condensed mesenchyme or dental
papilla, which encapsulates the enamel organ or the dental follicle
that later becomes the supporting tooth tissues.
4. Bell stage – Important changes happen in this stage.
The first change is the histo-differentiation. This histo-differentiation
begins at the late cap stage and continues to the bell stage.
The same epithelial cells develop into functionally distinct
components of the tooth. Cells at the center of the enamel organ
become the stellate reticulum.
The second change is the enamel organ becoming bell-shaped. This
occurs as the undersurface of the epithelial cap deepens and
the tooth crown develops its final shape.
The outer dental epithelium comes from the cuboidal cells at
the periphery of the enamel organ. While the inner dental epithelium
forms the cells on the border of the dental papilla. The cervical
loop is the meeting point of these two epithelia, which is found
at the rim of the enamel organ.
At this point, the cells continue to divide until the crown
grows to its full size. The tooth later gives rise to the epithelium
component of the root.
The next change happens with the occurrence of three events.
These are: (1) dental papilla is separated from the dental organ;
(2) the dental lamina fragments into numerous discrete epithelial
cell aggregates; and (3) the inner dental epithelium begins taking
shape of the tooth crown.
The fragmentation of the dental papilla is essential as it signifies
that tooth development continues inside the jaw tissues. This
is important occurrence for the tooth to function; it has to
penetrate the epithelium for it to reach the occlusion plane.
During the cap stage, nerve fibers start forming near the tooth
and grow toward the dental follicle. The nerves develop around
the tooth bud once they arrived there. They will then enter the
dental papilla. These nerve fibers never proliferate into the
Aside form the nerve fibers, it is in the cap stage that blood
vessels form in the dental follicle and enter the dental papilla.
Entrance of the dental papilla is formed by groups of blood vessels.
Number of blood vessels is determined and reached their maximum
number at the crown stage. The dental papilla then forms in the
pulp of the tooth.
Throughout a human beings life, the amount of pulp tissue in
a tooth decreases, meaning the blood supply of a tooth decreases
along with age. Since the enamel and the dentin is a mineralized
tissue, they do not have blood vessels for it get their needed
After these stages, tooth eruption occurs. Tooth eruption occurs
in three stages.
- Deciduous teeth stage – This occurs when the first
primary teeth appear.
- Primary dentition stage – This
occurs at six months of age and lasts until the six years
- Permanent dentition stage – This stage starts
around the 11 years of age.
Tooth eruption is influenced by many factors such as dentition
patterning. This determines specific tooth types and their positions
in the jaw. Animals have a homodont type of teeth, or their teeth
all have the same shape. Human teeth on the other hand, have
different shapes or are heterodont. Heterodont has three types,
namely: (1) incisiform; (2) caniniform; and (3) molariform.
There are two models that have been proposed to explain dentition
patterning. These are:
- Field model – This model proposed that the responsible
cells are present in the ectomesenchyme.
- Clone model – This
model proposes that each tooth type is derived from a clone
of ectomesenchymal cells that
by the epithelium to produce teeth of a given pattern.
But a new theory stated that the ectomesenchyme eventually assumes
a dominant role in dentition patterning. Molar development comes
from the recombination of molar papilla with the incisor dental
organ. Recombination of the incisor papilla with the molar dental
organ on the other hand, results in incisor development.