The entire primary dentition is initiated between 6 and 8 weeks of
The successional permanent teeth between week 20 in utero and 10
months after birth; and the permanent molars between week 20 in
utero (first molar) and 5 years of age (third molar).
Primary Epithelial Band
a continuous band of thickened
epithelium forms around the
mouth in the presumptive upper
and lower jaws. These bands are
roughly horseshoe-shaped and
correspond in position to the
future dental arches
Each band of epithelium will
give rise to 2 sub divisions:
1. Dental lamina
2. Vestibular lamina
continued and localized proliferative activity leads to the formation of
a series of epithelial outgrowths into the mesenchyme at sites
corresponding to the positions of the future deciduous teeth
A. Bud Stage
B. Cap Stage
C. Bell Stage
D and E. Dentinogenesis and
F. Crown formation
G. Root Formation and eruption
First incursion into the ecto-mesenchyme of the jaw.
Little change of the shape and function of epithelial cells
Condensation of ecto-mesenchyme.
Bud stage is characterized by rounded, localized growth of
epithelium surrounded by proliferating mesenchymal
cells, which are packed closely beneath and around the
In the bud stage, the enamel organ consists of
peripherally located low columnar cells and centrally
located polygonal cells
1. Tooth bud is separated from the dental lamina by lateral lamina.
2. Tooth germ will be called enamel organ.
3. Enamel niche, enamel knot, enamel cord, and stellate reticulum.
4. Dental papilla pulp and dentin.
5. Dental follicle or sac PDL and cementum.
6. Dental organ consists of (enamel organ, dental papilla, and dental
Condensation of the ectomesenchyme immediately subjacent to
the tooth bud caused by lack of extracellular matrix secretion by
the cells thus preventing separation. Histodifferentiation begins
at the end of cap stage.
Epithelial outgrowth called Enamel Organ because it will eventually
form the enamel
Dental Papilla: Ball of condensed ectomesenchymal cells (it will form
dentin and pulp). The peripheral cells adjacent to the inner dental
epithelium will enlarge and later differentiate into odontoblasts
Dental follicle or dental sac is the condensed
ectomesenchymal tissue surrounding the
enamel organ and dental papilla. This gives
rise to cementum and the periodontal ligament
(support structures for tooth)
Enamel niche: It is an artifact produced during
sectioning of the tissue. It occurs because the
enamel organ is a sheet of proliferating cells
rather than a single strand and contains a
concavity filled with ectomesenchyme
Enamel Knot: Densely packed accumulation of cells
projecting from the inner enamel epithelium into
dental papilla. Exact role not known, but currently
believed to be the organizational center for cusp
Continued growth leads to bell
stage, where the enamel organ
resembles a bell with deepening of the
epithelium over the dental papilla
Continuation of histodifferentiation
(ameloblasts and odontoblasts are
morphodifferentiation (tooth crown
assumes its final shape)
It can be divided into:
1. Early bell stage.
2. Late or advance bell stage.
Stellate reticulum: Star-shaped cells with processes, present between the
outer and the inner dental epithelium. They have a cushion-like consistency
that may support and protect the delicate enamel organ.
Outer Enamel Epithelium
Inner Enamel epithelium
Stratum intermedium: Cell layer between
the inner dental epithelium and stellate
reticulum which have high alkaline
phosphatase activity. They assist inner
enamel epithelium (ameloblasts) to form
A - dental papilla
B - inner enamel epithelial cells
C - outer enamel epithelium
D - stellate reticulum
E - stratum intermedium
F - odontoblasts
Cervical loop: Area where the inner
and the outer dental epithelium
meet at the rim of the enamel organ.
This point is where the cells will
continue to divide until the tooth
crown attains its full size and
which after crown formation will
give rise to the epithelium for root
You must remember the following:
Hard tissue formation starts at the late stages of the bell stage
Differentiation of cells into odontoblasts and ameloblasts
Dentin is formed before enamel
Dentin initiates the
formation of enamel