3. Embryo at 5-6 wiu
1
2
3
Caudal end
Cephalic end
1- frontonasal process
( forbrain)
2- developing heart
3- branchial arches
4. At 3 wiu: the stomodeum (primitive oral cavity)
develops as an invagination between the forebrain
and the primitive heart
5. At 5 wiu, the first branchial arch divides into mandibular &
maxillary processes to form the mandible & maxilla
6.
7. Histological structure of stomodeum
• The mucous membrane lining the stomodeum is
composed of:
1-Ectoderm,consists of 2-3 layers:
a-Basal cell layer( columnar in shape)
b- Superficial flattened cell layers.
2-ectomesenchyme:Consists of connective tissue.
3-Basementmembrane: between the ectoderm &
ectomesenchyme
1
2
3
8. Primary epithelial band formation
• The basal cell layer of the
ectoderm proliferate
firstly as islands of
epithelial outgrowths (4
island in maxillary arch
and 2 in mandibular arch)
in the underlying
ectomessnchyme.
• These islands grow to
coalesce together to form
horseshoe-shaped band
(in the position of the
future dental arches)
called primary epithelial
band .
9. Primary epithelial band
This primary epithelial band gives rise to 2
subdivisions:
1- Vestibular lamina: buccally located
2- Dental lamina: lingually located
10. VESTIBULAR LAMINA
• At 6 weeks of development , no
sulcus can be seen between the
cheek and tooth bearing areas
• The vestibule forms as a result of
the proliferation and enlargement
of vestibular lamina into the
ectomesenchyme.
• Its central cells degenerate (due
to lack of nutrition) and form a
cleft between the cheek and
tooth bearing areas
• This cleft becomes the oral (labial
and buccal )vestibule
Oral vestibule Dental lamina
12. DENTAL LAMINA
• So, The dental lamina appeared as
a horse show extension (from 1ry
epithelial band) invading the
underlying ectomesenchyme
• Histologically , the dental lamina is
composed of peripherally low
columnar cells resting on the
basement membrane and
centrally located polygonal cells
• This dental lamina is surrounded
by heavy condensation of
ectomesenchymal cells
13. Tooth development
• 10 deciduous teeth will develop
along the facial surface of the dental
lamina of each arch.
• At the sites corresponding to the
positions of the future deciduous
teeth, localized proliferative activity
appeared leading to the formation of
a bud outgrowths into the
ectomesenchyme called tooth germ
which will form the tooth
• Acc. To the shape of tooth germ ,
Tooth development now proceeds in
three stages: bud stage, cap stage
and bell stage which divided into
early bell and late bell stage
15. Morphological stages of tooth development
1- BUD-STAGE.
2- CAP-STAGE.
3- EARLY BELL-STAGE
4- LATE (ADVANCED)
BELL-STAGE
16. 1- BUD-STAGE
• The basal cells of dental lamina
divide to give bud outgrowths
represent the enamel organ (dental
organ), which histologically like that
of the dental lamina.
• The ectomesenchymal cells are
condensed below the tooth bud
representing dental papilla.
• the dental papilla& the enamel organ
are surrounded by ectomesenchymal
condensation called dental sac
(dental follicle).
• The enamel organ ,dental papilla&
dental sac form the tooth germ
18. 2- CAP-STAGE
A) The enamel organ
• The enamel organ grows unequally
to surround the growing condensed
ectomesenchyme.
• this leads to shallow invagination
giving a cap appearance to the
enamel organ.
• The cells of enamel organ
differentiate into:
1- Outer enamel (dental) epithelium
2- Inner enamel (dental) epithelium
3- Stellate reticulum
Outer enamel epithelium
inner enamel epithelium
Dental papilla
Dental sac
Dental lamina
19.
20. :Outer enamel epithelium
• single cuboidal cell layer resting on
basement membrane at the convex
surface of the enamel organ.
• It control the exchange of nutrient
between the enamel organ and dental sac.
Inner enamel epithelium:
• is columnar cells resting on basement
membrane in the concave site of the
enamel organ.
• It will elongate and help in formation of
enamel.
21. Stellate reticulum
• It occupies the central portion of the enamel organ . Its
cells appear as star shaped cells with wide intercellular
spaces
• this star shape is due to accumulation of intercellular
fluid (mucopolysaccharides) between The central
polygonal cells while they are attached to each other
by desmosomes.
• Its function:
I. Acts as a cushion to protect the ameloblast
II. Acts as a store-house for nutritive component
needed for the cells
III. Keep a room for developing enamel
22. Enamel knot and cord
• Enamel knot: It appears as a condensed
cells in the central portion of the enamel
organ near the inner enamel epithelium.
• Enamel cord: It is a vertical extension
from enamel knot connecting it to the
outer enamel epithelium .
• Both enamel knot& cord are transient
structures and its functions is unknown
but:
1-they might be an artifact
2-may give rise to other cell layer (stratum
intermedium).
3- may acts as a signaling center: it express
growth factors needed for determination of
tooth morphology.
Enamel knot
Enamel cord
23. B) Dental papilla
• It is the condensation of the
ectomesenchymalcells in the
invaginated portion of the
enamel organ.
• It provide nutrition to the
enamel organ
• The inner enamel epithelium
is separated from the dental
papilla by cell free zone
(acellular zone): it is free of
cells but contain cytoplasmic
processes & fine
argyrophilicfibers).
24. C) Dental sac
• it is ectomesenchymal tissue surround dental
papilla and enamel organ
• It becomes more denser to provide
reinforcement preventing distortion of outer
enamel epith.
