2. Dental lamina
• During the fifth
week of
embryonic
development, the
oral epithelium
thickens along the
future dental
arches to form the
dental lamina.
Legend: A, dental lamina; B, Mesenchymal neural crest
3. Bud stage
• Around the eighth week of
embryonic development, the
mesenchymal neural crest
induces the development of
tooth buds at ten locations
in the upper and lower
dental lamina.
• During the bud stage the
dental lamina grows into the
mesenchyme in the shape of
a bud.
4. Cap stage
• During the ninth week of
embryonic development, the
tooth bud differentiates into a
cap-shaped enamel organ
extending from the dental
lamina.
• A vestibular lamina develops to
separate the gum from the
lip/cheek.
• During the cap stage, an unequal
growth of epithelial cells grows
down to form a concavity around
the mesenchyme forming the
dental papilla.
• Other mesenchymal cells encircle
the enamel organ forming the
dental sac.
Legend: A, Enamel organ; B, Dental lamina; C, Vestibular
lamina; D, Dental Papilla; E, Dental sac
5. Bell stage
• Cytodifferentiation becomes
apparent during the bell stage,
when the epithelial cells
outlining the enamel organ can
be distinguished as the inner
enamel epithelium and outer
enamel epithelium.
• The interior of the enamel
organ comprises the stellate
reticulum, a cushiony layer
which will protect the
developing tooth.
• The successional lamina, which
will give rise to the secondary
tooth, arises from the dental
lamina.
A, Inner enamel epithelium; B, Outer enamel epithelium;
C, Stellate reticulum; D, Successional lamina; E, Dental
lamina; F, Dental papilla; G, Dental sac.
6. Cervical loop
• The inner enamel epithelium and
outer enamel epithelium joint at
the cervical loop, that portion of
the enamel organ which is growing
down into the mesenchyme.
• The cells of the inner enamel
epithelium will eventually become
ameloblasts.
• The layer adjacent to the inner
enamel epithelium is the stratum
intermedium, and will become
important in transporting nutrients
to the future ameloblasts.
Legend: A, Cervical loop; B, Inner enamel epithelium;
C, Outer enamel epithelium; D, Stratum intermedium;
E, Stellate reticulum
7. Cytodifferentiation of inner enamel
epithelium
• The cells of the inner
enamel epithelium
(which will become
ameloblasts) are least
differentiated near the
cervical loop and most
differentiated near the
incisal cusp of the
tooth.
Legend: A, Cervical loop; B, Least differentiated;
C, Most differentiated
8. Odontoblastic differentiation
• Preameloblasts initiate
the differentiation of
odontoblasts which arise
from cells in the dental
papilla. The odontoblasts
are called
preodontoblasts before
they begin the production
of dentin. Legend: A, Preameloblasts; B, Preodontoblasts;
C, Stellate reticullum; D, Dental papilla
9. Deposition of dentin and enamel
• Mature, elongated odontoblasts
begin the deposition of
predentin.
• This deprives the preameloblasts
of their nutritional source
inducing their differentiation into
ameloblasts which then begin to
deposit enamel.
• Predentin is completely organic
when it is formed and gradually is
mineralized to form dentin.
• Enamel is partially mineralized
when it is deposited.
• Arrows show the direction of
movement of ameloblasts and Legend: A, Odontoblasts; B, Predentin;
odontoblasts. C, Ameloblasts; D, Enamel; E, Dentin.
10. Reduced enamel epithelium
• Following the formation of the
crown , the enamel organ
collapses to form the reduced
enamel epithelium which
covers the tooth through
eruption.
• The reduced enamel epithelium
consists of the
mature/protective ameloblasts
and remanants of the outer
layers of the enamel organ.
• Numerous capillaries,which had
formed to supply oxygen and
nutrients to the ameloblasts
following dentin formation, Legend: A, Reduced enamel
surround the reduced enamel epithelium; B, Maturative/protective
epithelium. ameloblasts; C, Capillary
11. Immature enamel
• Ameloblasts
secrete immature
enamel which is
only partially
mineralized.
Legend: A, Ameloblasts; B, Immature enamel
12. Preodontoblast
• Prior to dentinogenesis
the basement
membrane thickens
between the
preodontoblast and
preameloblast.
• Processes from the
preodontoblasts extend
through the basement
membrane to come into
close association with
the preameloblast.
Legend: A, Preodontoblast; B, Preameloblast;
C, Basement membrane
13. Odontoblast
• Following differentiation of
preodontoblasts into
odontoblasts, dentin begins
to be deposited first as
predentin.
• The odontoblasts nucleus has
moved away from the
secretory end of the cell
where numerous organelles
have accumulated to aid in
predentin deposition.
Legend: A, Odontoblast nucleus; B, Secretory
end of odontoblast; C, Predentin
14. Ameloblasts
• After dentinogenesis begins, the
preameloblasts differentiate
into ameloblasts which begin to
deposit enamel.
• Ameloblasts are very tall
columnar cells with a nucleus
displaced away from the
secretory end of the cell. The
ameloblasts develop a Tome's
process shortly after beginning
amelogenesis.
• This process is responsible for
the production of enamel in the
form of rods.
Legend: A, Ameloblast nucleus; B, Enamel;
C, Tome's process
15. Maturative ameloblast
• When the ameloblast has finished
depositing enamel, the Tome's
process is lost and a striated
border takes its place.
• During the maturation stage,
there is a loss of organic material
and water from the enamel.
• The striated border is supposedly
responsible for the resorption of
these matrix components, as
evidenced by numerous dense
granules within the apical
cytoplasm of the ameloblast.
A, Striated border; B, Immature enamel;
C, Mature enamel; D, Dense granules
16. Calcification
• Enamel and dentin is
fairly evenly calcified in
the erupted deciduous
tooth (1) but a gradient
of calcification can be
seen in the developing
permanent tooth (2)
with the more calcified
areas located in the
incisal areas (arrow)
Legend: A, Enamel; B, Dentin
18. More mature enamel
• Enamel is made up of
elongated groups of
hydroxyapatite crystals
called rods.
• Hydroxyapatite crystals
run parallel to the long
axis of the rod core (B)
and obliquely in the rod
sheath (A).
• In maturing enamel the
hydroxyapatite crystals
become thicker.
Legend: A, Rod sheath; B, Rod core
19. Root formation
• After complete formation of the
crown of the tooth, the root is
formed.
• An extension of the enamel organ,
called the epithelial root sheath of
Hertwig, continues to grow apically.
• The epithelial root sheath induces
the differentiation of odontoblasts
which form root dentin.
• The apical most portion of the root
sheath turns inward toward the
radicular pulp cavity (that portion of
the pulp cavity inside the root) and is
A, Epithelial diaphragm;
called the epithelial diaphragm.
B, Radicular pulp cavity;
C, Dentin; D, Enamel
space; E, Alveolar Bone;
F, Root
20. Epithelial root sheath
• The epithelial root sheath is
made up of inner and outer
enamel epithelial layers
without the other two
interposing layers.
• Following the induction of
odontoblast and dentin
formation, the epitheal
root sheath disintegrates
forming epithelial rests,
small groups of epithelial
cells that can remain
around the root.
A, Radicular pulp cavity; B, Dentin; C, Dental sac;
D, Point at which epithelial root sheath begins to
disintegrate; E, Epithelial diaphram
21. Cementum formation
• As the epithelial root
sheath breaks down, cells
from the dental sac
migrate to the surface of
the root dentin and
differentiate into
cementoblasts.
• These cells lay down
cememtum on the surface
of the root.
A, Cementoblasts; B, Odontoblasts; C, Predentin
22. Epithelial rests
• Remnants of the disintegrated
root sheath called epithelial
rests can remain for long
periods of time following
eruption of the tooth.
• The first dentin that is formed is
called mantle dentin, while the
remaining dentin is called
circumpulpal dentin.
• There is also a small layer
interposed between these two
dentin layers of less mineralized
dentin called globular dentin.
A, Epithelial rests; B, Mantle dentin; C,
Globular dentin; D, Circumpulpal dentin
23. First maxillary deciduous molar
• This molar is from a 22-
week fetus.
• The red coloration
indicates the formation
of the hard tissues.
• Enamel and dentin are
first formed at the cuspal
region and their
formation proceeds
toward the cervix of the
tooth. Legend: A, Cusp of molar
24. Second maxillary deciduous molar
• This molar is from a
19-week fetus.
• The first deposited
dentin on the
mesiobuccal cusp is
shown.
Legend: A, Dentin on the mesiobuccal cusp
28. أدعيه قبل المذاكره وبعدها...
قبل المذاكرة
اللهم أنً اسألك فهم النبٌٌن و حفظ المرسلٌن و المالئكة المقربٌن ، اللهم أجعل ألسنتنا عامرة بذكرك و قلوبنا بخشٌتك و أسرارنا
بطاعتك أنك على كل شًء قدٌر .. حسبنا هللا و نعم الوكٌل
بعد المذاكرة
اللهم أنً استودعتك ما قرأت و ما حفظت و ما تعلمت فرده عند حاجتً الٌه انك على كل شًء قدٌر ، حسبنا هللا و نعم الوكٌل
يوم اإلمتحان
اللهم أنً توكلت علٌك و سلمت امري الٌك ال ملجأ و منجا منك إال الٌك
دخول القاعة
رب أدخلنً مدخل صدق و أخرجنً مخرج صدق و أجعل لً من لدنك سلطانا نصٌرا
قبل البدء بالحل
رب أشرح لً صدري و ٌسر لً أمري و احلل عقدة من لسانً ٌفقه قولً بسم هللا الفتاح ، اللهم ال سهل أال ما جعلته سهال و انت تجعل الحزن اذا
شئت سهال ٌا ارحم الراحمٌن
أثناء األمتحان
ال إله اال انت سبحانك أنً كنت من الظالمٌن ٌا حً ٌا قٌوم برحمتك أستغٌث ، رب ان مسنً الضر أنك أرحم الراحمٌن
عند النسيان
اللهم ٌا جامع الناس فً ٌوم ال رٌب فٌه أجمعنً و ضالتً
بعد األنتهاء
الحمد هلل الذي هدانا لهذا و ما كنا لنهتدي لوال أن هدانا هللا
