Oral Histology 1st Lecture

1. UP TO DATE
IN
ORAL BIOLOGY AND EMBRYOLOGY
Prof. Dr. Nahed A. Khalil
Head of Oral Biology Department
&
Contributing Staff Members
Faculty of Oral &Dental Medicine
Cairo University

3. At the age of 5-6 W.I.U.L. the primitive oral cavity is
lined by ectoderm composed of 2 -3 layers, basal
columnar & superficial flat cells.
The mesoderm containing ectomesenchymal cells is
separated from the oral ectoderm by a basment
membrane

4. At 5-6 w.i.u.l Embryo
HHeeaadd
SSttoommooddeeuumm
Heart
Basement
membrane
ECTODERM
MESODERM

5. The Morphological stages of tooth
development are:
1- dental lamina formation
2- Bud stage
3- Cap stage
4- Bell stage : which is divided into :
-* Early bell stage (before dentin formation).
-* Advanced (Late) bell stage (after formation of the 1st
layer of dentin).

6. 1- Dental lamina formation
Under the influence of the ectomesenchyme (neural crest cells),
ectodermal proliferation in the underlying connective tissue takes
place in separate islands that coalesce to form a band exhibiting
a horse shoe shape in the upper & lower jaws. This band is called
the tooth band or the dental lamina.

7. SSttaaggee ooff ddeennttaall llaammiinnaa--11
Flat cells
Columnar cells
At 6-7 W.I.U.L
Ectoderm
Basement
membrane
Ectomesenchymal tissue

8. Condensation of
ectomesenchymal cells occurs
around epithelial proliferation
at certain sites on the labial
surface of the dental lamina.
Each site represents one of the
deciduous teeth.
From this point tooth
development proceeds in 3
stages describing the
morphology of the developing
tooth germ: Bud, Cap & Bell.

9. 2-Bud stage
The cells of the dental lamina
proliferates on the labial side of
dental lamina forming rounded
buds called the dental or enamel
organ.
The ectomesenchyme condenses
below the enamel organ & is called
the dental papilla.
The ectomesenchyme that encircle
both the enamel organ & the
dental papilla is called dental sac

10. ((BBUUDD SSTTAAGGEE ((aatt 88-- WWIIUU--22
DENTAL
ORGAN
DENTAL
PAPILLA
DENTAL SAC
TOOTH
GERM

11. The vestibular lamina is
formed as ectodermal
proliferation in the
underlying
ectomesenchyme buccal
to the dental lamina.
Epithelial degeneration
occurs inside the
vestibular lamina to
form the oral vestibule
separating the cheek &
lip from the teeth
bearing area. Oral
vestibule
Teeth buds

12. Cap stage
Differential growth
results in increase in the
size of the enamel organ
& change in its shape to
exhibit a cap shape with
short & broad connection
to the dental lamina.
The cap- shaped enamel
organ has a convex outer
surface & concave inner
surface.

13. CCAAPP SSTTAAGGEE--33
TOOTH
GERM At 9-10 WIU
1-
DENTAL
ORGAN
2- DENTAL
PAPILLA
3-
DENTAL
SAC

14. CCaapp ssttaaggee
1- Outer enamel epithelium:
A single layer of cuboidal cells with
deeply stained rounded nuclei arranged
on the convex surface of the enamel
organ
2- Inner enamel epithelium:
A single layer of columnar cells with
deeply stained rounded nuclei arranged
on the concave surface of the enamel
organ.
A basement membrane separates the
inner & outer enamel epithelia from the
dental papilla & the dental sac
respectively.

15. CCaapp ssttaaggee
3- Stellate reticulum:
Star shaped cells with long processes
anastomse with each other by desmosomes.
4- Enamel Knot:
A condensation of ectodermal cells in the
central region of the inner enamel
epithelium that may bulge towards the
dental papilla.
It extends towards the outer enamel
epithelium forming a strand of cells
(Enamel cord).
They are both transient structures
They may have a role in determining the
cusp position in molars, or may give the
stratum intermedium in the bell stage

16. CCAAPP SSTTAAGGEE(( 33
Enamel knot
Inner D. E.
Outer D. E.
Stellate R.
Enamel cord
Dental Sac Dental Papilla.

17. The bell stage
Differential growth accompanied by
Histodifferentiation &
Morphodifferentiation leads to increase
in size & shape of the enamel organ to
exhibit a bell shape.
It is divided into:
Early bell stage: before any hard tissue
formation
Advanced or late bell stage: which
begins by formation of the first layer of
dentin.

18. EEaarrllyy bbeellll ssttaaggee--44
At 11-12 WIU
1- The dental lamina:
*Break up of the dental lamina
by mesenchymal invasion divides
it into:
Main dental lamina:
(carrying permanent successors)
Lateral dental lamina : which
become long & narrow
connecting the E. Org. of
deciduous teeth to the main
dental lamina.

19. EEaarrllyy bbeellll ssttaaggee
2- The enamel organ:
* The outer enamel
epithelium:
the cells decrease in
height & become low
cuboidal.

20. EEaarrllyy bbeellll
ssttaaggee
* The inner enamel epithelium:
(IEE) (Preameloblasts)
* The columnar cells elongate towards
the dental papilla at the expense of the
cell free zone to exhibit 40 microns length
& be on contact with the un-differentiated
M Cs. of the dental papilla causing an
organizing influence on them to
differentiate into Odontoblasts a process
called induction.
*They show alteration in functional
polarity in which the nucleus &
mitochondria migrate towards the
proximal end while the Golgi &
centerioles migrate towards the distal end.

21. * Cervical loop:
The outer & inner enamel
epithelium meet at the cervical
part of the enamel organ
The inner enamel epithelium
reflects on the outer E.E. for a
short distance.
It may contain small amount
of stellate reticulum.(rare)

22. Early bell stage
•The stellate reticulum:
* The star shaped cells of the st.
reticulum are connected to each
other, to the cells of the O.E.E. &
to the st. interm. by desmosomes
* The glucosaminoglycans are
hydrophilic & attract water into
the center of the enamel organ to
keep space for the developing
enamel.

23. Early bell stage
Stratum intermedium
* 2-3 layers of flat cells between
inner E.E. & the stellate reticulum
& are connected to both of them
by desmosomes
* they are rich in alkaline
phosphatase enzyme essential for
enamel mineralization.
*With the ameloblasts, they are
considered as a functional unit in
enamel formation &
mineralization.
* They control fluid diffusion into
& out of the ameloblasts.

24. EEaarrllyy bbeellll ssttaaggee--44
Stellate
Reticulum
Cervical
loop
At 11-12 WIU
ODE
Preameloblasts
Stratum
Intermedium

25. EEaarrllyy bbeellll ssttaaggee--44
Dental
papilla
At 11-12 WIU
Odontoblasts
Dental sac

26. Inner Enamel Epithelium
Odontoblasts
Dental Sac
EEaarrllyy bbeellll ssttaaggee--44

27. EEaarrllyy bbeellll ssttaaggee--44
SR
SI
Preameloblast
DP
OB

28. EEaarrllyy bbeellll ssttaaggee--44

29. SSUUCCCCEESSSSIIOONNAALL LLAAMMIINNAA
DENTAL LAMINA
PROPER
SUCCESSIONAL
LAMINA
LATERAL DENTAL LAMINA
Dental Organ
SUCCESSOR
PRIMORDIUM

30. DDeennttiinn MMaattrriixx FFoorrmmaattiioonn
Odontoblasts differentiation Early dentin formation

31. 5-Advanced (Late) bell stage

32. The Advanced Bell Stage
Deposition of the first layer of
dentin by the differentiated
odontoblasts, causes many
changes in the different layers of
the tooth germ:
1- The lateral dental lamina:
breaks up into islands of
epithelial cells called Serres
pearls or epith. Rests of Serrs
which separates the developing
tooth from the oral epith.

33. 2- The outer enamel
epithelium:
Formation of dentin breaks up
the nutrition coming via the
dental papilla. Therefore:
* Folding of the outer E.E. will
increase the surface area for
increased nutrition.
The vascular inner layer of the
dental sac brings its Capillary
loops very close to the cells of the
enamel organ, providing it with a
rich source of nutrition.
* The cells of the outer E.E.
become flat, develop microvilli
& show increased mitochondria

34. The Advanced bell stage
3-The inner E.E. (Ameloblasts):
* The newly formed dentin exerts an influence on the inner enamel
epithelium to differentiate into ameloblasts, a process called reciprocal
induction.
* The ameloblasts are 40 microns in length & 4-5 microns in diameter
& in cross section they are hexagonal in shape. They are attached to
each other by junctional complexes & to the stratum intermedium by
desmosomes.

35. 4-Stellate reticulum:
Undergo shrinkage
The intercellular fluid is utilized in
nutrition & the space is utilized by
the formed enamel
5-Stratum intermedium:
*Its cells show high alkaline
phosphatese enzyme
activity that is important
for enamel mineralization.

36. AAddvvaanncceedd ((LLaattee)) bbeellll ssttaaggee--55
STRATUM
INTER.
STELLATE
RETICULUM
PREDENTIN
ODONTOBLASTS
AMELOBLAST

37. 5-Advanced (Late) bell stage
OUTER DENTAL
EPITHELIUM
CAPILLARY LOOP
ENAMEL
MATRIX
DENTIN
PREDENTIN
SR
AB
SI

38. 5-Advanced (Late) bell Stage
D
PD
OB
Dental
papilla
E matrix
SR
SI
AB

39. VESTIBULAR DDEENNTTAALL LLAAMMIINNAA
LAMINA

41. Stages of tooth development are also
described according to physiologic changes
& function during development & are
called histophysiological stages.
These include:
1- Initiation 2- Proliferation
3- Histodifferentiation
4- Morphodifferentiation
5- Apposition

42. RRoooott FFoorrmmaattiioonn
Cervical loop
Hertwig’s epith.
root sheath
Odontoblast
differentiation
Dentin formation
Disintegration
of root sheath
Cementoblast
differentiation

43. Root formation
Begins when the enamel & dentin
formation reaches the future
cemento-enamel junction.
The epithelial cells of inner & outer
enamel epithelium proliferate from
the cervical loop to form a double
epith. membrane known as
Epithelial root sheath of Hertwig.
* It bends forming obtuse angle to
the enamel organ at the future
cemento-enamel junction to form the
epithelial diaphragm.

44. Root formation
* The inner enamel epithelium in the epithelial
root sheath of Hertwig, will induce U.D.M.Cs of
the dental papilla to differentiate into
Odontoblas which form the 1st layer of root
dentin.
* The Epithelial root sheath of Hertwig
degenerates forming epithelial rests of Mallassez
* The formed dentin that come in contact with
the dental follicle, induces the differentiation of
U.M.Cs. in the dental follicle in to
cementoblasts which lay down cementum.
* This occurs in the formation of single rooted
tooth.
Proliferation zone
cementoblasts

45. Cervical loop Hertwig’s epith.
root sheath

46. Odontoblast
differentiation

47. Dentin formation
Disintegration
of root sheath
Cementoblast
differentiation

48. EEPPIITTHHEELLIIAALL DDIIAAPPHHRRAAGGMM

49. Epithelial diaphragm

50. NNEEWWLLYY FFOORRMMEEDD RROOOOTT

51. MMUULLTTII--RROOOOTTEEDD TTOOOOTTHH

52. Formation of multi- rooted teeth
* The root trunk of molars is formed like single rooted tooth.
* At the bifurcation area, the epithelial diaphragm produces 2 or 3
tongue- like processes in case of 2 rooted & 3 rooted teeth.
* The processes grow towards each other & fuse dividing the wide root
trunk into 2 or 3 roots.
* Each one of these roots proceeds in development as in single rooted
tooth.

53. MMUULLTTII--RROOOOTTEEDD TTOOOOTTHH

54. Clinical consideration
Formation of accessory root canals :
Causes: 1) When the Hertwig’s epithelial root sheath looses its
continuity before odontoblastic differentiation & dentin formation.
2) Failure in fusion of the tongue –like processes of the epithelial
diaphragm in the pulpal floor.
3) If a large blood vessel is present and disturb the continuity of the
epithelial root sheath.
* If the continuity of the epithelial root sheath of Hertwig is broken
after odontoblastic differentiation & before dentin formation,
intermediate cementum will be deposited.
* if the epithelial root sheath of Hertwig remains adherent to the
dentin surface, its inner cells may differentiate into ameloblasts &
produce enamel, known as Enamel pearls.

55. EENNAAMMEELL PPEEAARRLL ENAMEL PEARL

56. TTeesstt yyoouurrsseellff Stellate reticulum
Stratum intermedium
Ameloblasts
Enamel matrix
Dentin
Predentin
Odontoblasts
Dental papilla