Oral histology

1. DISCIPLINE; BSC (HONS) DENTAL TECHNOLOGY
MODULE NAME; ORAL HISTOLOGY
CLASS; SECOND YEAR
LECTURE TITLE; ENAMEL: COMPOSITION, FORMATION &
STRUCTURE (chapter 7)
DELIVERED BY; DR. SADIA AWAIS
LECTURE DATE; 13-04-2020 to 20-04-2020

2. AMELOGENESIS
INTRODUCTION
AMELOGENESIS is the process of
formation of enamel by cells
called “ameloblasts” which
originate from the embryonic
germ layer known as ectoderm.

3. DEVELOPMENT OF TOOTH
 stomatodeum lined by stratified
squamous epithelium covering
connective tissue which originates
from neural crest called
ectomesenchyme
 at 27th day stomatodeum connected
with forgut by rupture of
buccopharyngeal membrane

4. PRIMARY EPITHELIAL BAND
 AFTER 37 DAYS OF DEVELOPMENT
 THICKENED EPITHELIAL BAND FORMED
INCREASD PROLIFERATIVE ACTIVITY CHANGE IN
ORIENTATION OF CELLS
 two subtypes
I. DENTAL LAMINA
II. VESTIBULAR LAMINA

5. ORAL EPITHELIUM PRIMARY EPITHELIAL BAND DENTAL LAMINA

6. DENTAL LAMINA
TWO OR THREE WEEKS AFTER RUPTURE OF
BUCCOPHARANGEAL MEMBRANE
BASAL CELLS OF ORAL ECTODERM PROLIFERATE MORE
RAPIDLY THAN ADJACENT CELLS
FORMATION OF DENTAL LAMINA
DISTAL LINGUAL
EXTENSION EXTENSION
PERMANENT REMAINING
MOLARS TEETH

7. VESTIBULAR LAMINA
 CELLS RAPIDLY PROLIFERATE INTO
ECTOMESENCHYME AND DEGENERATE
 DEVELOP LABIAL AND BUCCAL TO DENTAL LAMINA
 ALSO TERMED LIP FURROW BAND

8. DENTAL & VESTIBULAR
LAMINA
At 7th week of I.U.L…
A- vestibular lamina
B- dental lamina

9. STAGES OF TOOTH
DEVELOPMENT
I. BUD STAGE
II. CAP STAGE
III. BELL STAGE

10. BUD STAGE
 8th week of I.U.L…
Epithelium of dental lamina
Separated from ectomesenc hyme by
basement membra-
ne.
Round oval swellings arise from
basement membrane at
10 points leading to initiation of tooth germ
 Peripheral cells low columnar; central polygonal

11. CAP STAGE
11th weekof I.U.L…
EARLY CAP STAGE:
Peripheral cuboidal cells-
-- Outer Enamel
Epithelium
Tall columnar cells in the
concavity ---
Inner Enamel Epithelium
Rounded cells in the
central portion

12. CAP STAGE
12th weekof I.U.L…
LATE CAP STAGE:
Peripheral cuboidal cells---
Outer Enamel Epithelium
Tall columnar cells in the
concavity ---
Inner Enamel Epithelium
Polygonal cells b/w Outer &
Inner EE form a cellular
network--- Stellate
Reticulum

13. ENAMEL KNOT/CORD/NICHE
Enamel knot : localized thickening in internal dental
epithelium at centre of tooth germ.
Enamel cord/septum : strand of cells running from knot
to external dental epithelium
FUNCTION: as reservior of cells; determine initial position
of 1st cusp formation; express genes for many
signalling molecules eg. BMP which direct growth of
surrounding epithelium and mesenchyme.
Enamel niche: apparent structure in histological section
as concavity filled with CT

15. ENAMEL CORD

16. ENAMEL NICHE

17. BELL STAGE
14th week of I.U.L…
4 distinct layers:
.Outer Enamel Epithelium
.Stellate reticulum
.Stratum intermedium
. Inner Enamel Epithelium
Early Bell Stage

18. OEE:
Cells Flattened To Low Cuboidal
Form with High Nuclear /Cytoplasmic
Ratio.
IEE:
 Consists of a single layer of cells that
differentiate prior to amelogenesis into tall
columnar cells called ameloblasts.

19. Attached to each other by junctional
complexes
laterally & to the stratum intermedium by
desmosomes.
They have an organizing influence on the
mesenchymal cells of the dental papilla which
differentiates into odontoblasts.

20. Before enamel formation begins the stellate
reticulum collapses reducing the distance
between the ameloblasts & the capillaries
between the OEE.
:
Formed by differentiation of epithelial cells
between the IEE and s. reticulum.

21. Closely attached by desmosomes and gap
junctions. Well-developed cytoplasmic
organelles, acid mucopolysaccharides, high
glycogen content.
Basement membrane that separates the
enamel organ and the dental papilla just
prior to dentin formation is called
MEMBRANA PREFORMATIVA.

22. TWO IMPORTANT EVENTS
1. Dental lamina joining the tooth
germ to the oral epithelium
breaks up into discrete islands of
epithelial cells thus separating
the developing tooth from the
oral epithelium .
2. IEE folds making it possible to
recognize the shape of the future
crown pattern of the tooth.

23. Crown pattern formation
When tooth germ is growing during early bell stage cell
division occurs throughout IDE
Cessation of cell division at particular point
Point at which IDE cell maturation 1st occur represent
growth centre
At cervical loop IDE constrained and there is continued
proliferation of cells leading to buckle formation
Gradually maturation sweeps down cusp slope

24. Crown Pattern
Determination

25. VASCULAR SUPPLY
 CLUSTERS OF BLOOD VESSELS AROUND TOOTH GERM
ENTERING DENTAL PAPILLA DURING CAP STAGE
 NO. INCREASE DURING HISTODIFFERENTIATION
 MAXIMUM AT CROWN STAGE OF DEVELOPMENT
 AS AGE INCREASE BLOOD SUPPLY GETS REDUCED
 BEFORE DENTIN FORMATION; DENTAL PAPILLA
 IN BETWEEN; GLYC OGEN STORES AND STELLATE
RETICULLUM

26. NERVE SUPPLY
 nerve fibre approach during bud, cap stage
 Initial innervation sensory
 Rich plexus around tooth germ

27. LIFE CYCLE OF AMELOBLAST
Amelobasts are the cells
derived from the IEE that
forms enamel.
Stages of life cycle-
1.MORPHOGENIC STAGE
2ORGANISING STAGE
3.FORMATIVE STAGE
4.MATURATIVE STAGE
5.PROTECTIVE STAGE
6.DESMOLYTIC STAGE

28. MORPHOGENIC STAGE
 During bell and crown stage of tooth development
cells of dental organ along with dental papilla form
crown
 Cells of internal dental epithelium are cuboidal or
low columnar with centrally placed nuclei.
 Golgi elements in proximal portion of the cells.
 Mitochondria and other cytoplasmic components
are scattered throughout.

29. ORGANISING STAGE
 Connective tissue cells become odontoblasts & starts dentine
formation
 Cells of IEE become longer ,with nucleus contained in proximal
end and centriols, golgi body towards distal end
 Acidophilic granules found in proximal parts are mitochondria.
 Disappearance of cell free zone

30. FORMATIVE STAGE
• Odontoblast induce the cells of inner
enamel epithelium to form Ameloblasts.
• Ameloblast shows proximally placed
nucleus and high amount of rough E.R.,
high amount of golgi complex, and
ribosomes along the distal part of the cell.
• The cells of enamel organ deriving its
nutrition from adjacent dental papilla is
now cut off. The cells of enamel organ
have to depend for its nutrition from
dental sac, hence there is proliferation of
vasculature in dental sac

31. MATURATIVE STAGE
 Reduction in height of ameloblast
 Decrease in volume & organalle content
 Ameloblast form
-rough border(introduction of inorganic content)
-smooth border(removal of protein &water)
-

33. PROTECTIVE STAGE
 Protection of newly formed enamel surface from
follicular connective tissue
 Ameloblast no longer differentiated from stratum
intermedium & outer enamel epithelium
 Formation of reduced enamel epithelium

35. DESMOLYTIC STAGE
 Reduced enamel epithelium secrete enzymes that
destroy connective tissue causes eruption of tooth
 Premature degeneration of r
reduced enamel epithelium
prevents eruption of teeth

37. AMELOGENESIS
 Amelogenesis has been subdivided into three main phases (Tencate)
1) Pre-secretory Morphogenetic
Differentiation
2) Secretory
3) Maturation Transitional
Maturation Proper

38. MORPHOGENETIC STAGE
 The cells are cuboidal or low columnar, with large centrally
located nuclei and poorly developed golgi apparatus in
proximal part of cell, where junctional complex occur.
 Mitochondria and other cytoplasmic components
scattered throughout cells

39. DIFFERENTIATION PHASE
THE BASAL LAMINA IS
FRAGMENTED BY CYTOPLASMIC
PROJECTIONS.
INNER ENAMEL EPITHELIUM
DIFFERENTIATE INTO AMELOBLASTS-
THEY ELONGATE AND NUCLEI SHIFT
PROXIMALLY.
GOLGI APPARATUS, RER AND
MITOCHONDRIA CLUSTER IN DISTAL
REGION. SECOND JUNCTIONAL
COMPLEX OCCURES IN THIS REGION.
TOMES PROCESS- DISTAL
EXTENSION OF AMELOBLAST, AGAINST
WHICH ENAMEL FORMS.

41.  Adjacent ameloblasts are aligned
closely with each other with the
help of junctional complexes.
 These complexes encircle the cell at
their distal and proximal end.
 Fine actin containing filaments
radiate into cytoplasm of
ameloblast. Forming distal and
proximal webs.

42. SECRETORY STAGE
 In this phase the cells acquire intense secretory activity.
The golgi complex is extensive and surrounded by
numerous cisternae of RER.
 m-RNA for enamel proteins are translated by ribosomes on
the membrane of Endoplasmic Reticulum, modified by the
Golgi and packaged into secretory granules.
 These granules migrate to the distal extremity of cell, that is
into tomes process.

43. WHEN ENAMEL FORMATION
BEGINS, TOMES PROCESS COMPRISE
ONLY A PROXIMAL PORTION.
SECRETORY GRANULES MIGRATE &
ITS CONTENTS RELEASED AGAINST
NEWLY FORMED MANTLE DENTINE
TO FORM INITIAL LAYER OF ENAMEL
THAT DOES NOT CONTAIN ENAMEL
RODS.
AS INITIAL LAYER FORMED
AMELOBLAST MIGRATE AWAY
FROM DENTINE, AND DEVELOP
DISTAL PORTION OF TOMES PROCESS
AS AN OUTGROWTH OF PROXIMAL
PORTION.

44. PTP(PROXIMAL TOMES PROCESS) EXTENDS FROM THE
DISTAL JUNCTIONAL COMPLEX TO THE SURFACE OF THE
ENAMEL LAYER.
THE DTP(DISTAL TOMES PROCESS) INTERDIGITATES INTO
THE ENAMEL BEYOND THE INITIAL LAYER THAT IS FROM
PTP.
THE CYTOPLASM OF BOTH PROCESSES IS CONTINUOUS
WITH THAT OF THE BODY OF THE AMELOBLASTS.

45.  On establishment of tomes process enamel protein secretion
confined to two sites
 First site –formation of enamel matrix wall.walls enclose pit into
which tomes process fits
 Second site-fills this pit with matrix
later walls-become interrod enamel ;infilling becoming rod

48. The dTP lengthens as the enamel layer
thickens & thinner as the rod grows in
diameter.
dTP eventually squeezed out of existence
creating a narrow space along the most of
circumference between rod and interrod
enamel that fills with organic materials and
forms rod sheath.

49. BEFORE THE SECRETION OF FINAL FEW
INCREMENT, AMELOBLASTS LOOSE THEIR
TOMES PROCESS. sO, ENAMEL RODS ARE
NOT PRESENT IN THIS LAYER.
HENCE IN CONCLUSION, THE PRISMATIC
ENAMEL LAYER IS SANDWICHED
BETWEEN THE INITIAL PRISMLESS LAYER
AND FINAL PRISMLESS LAYER OF
ENAMEL.

50. MATURATION-TRANSITIONAL PHASE
 Reduction of Ameloblast height and a
decrease in their volume and organelle content.
 Ameloblasts undergo progressive cell death
(apoptosis ) upto 50% to permit orderly
morphogenesis.
 Just after completing the transitional phase,
ameloblasts deposit a basal lamina at their
flattened apex .

51. MATURATION PROPER
 Ameloblasts become involved in the removal
of water and organic material to introduction
of additional inorganic materials.

Characterized by - cyclic creation, loss
and recreation of highly invaginated ruffle-ended
apical surface.

52. Significance of modulation
is unknown – could be
related to maintain an
environment that allows
accretion of mineral content
and loss of organic matrix.
Ruffle ended ameloblasts show endocytic
activity and contain numerous
lysosomes,calcium binding proteins,
membrane associated calcium adenosine
triphosphatases that appear to promote the
pumping of calcium ions into maturing ename
Smooth ended ameloblast-leak small proteins

53. RUFFLE ENDED AMELOBLASTS POSSES LEAKY
PROXIMAL JUNCTIONS AND TIGHT DISTAL
JUNCTIONS WHEREAS SMOOTH ENDED
AMELOBLASTS HAVE LEAKY DISTAL
JUNCTIONS AND TIGHT PROXIMAL
JUNCTIONS.

54. Withdrawal of matrix is attributed to the action of
bulk degrading enzymes that act extracellularly to
digest the various matrix proteins into fragments
small enough to be able to leave the enamel layer.

55.  Mineralization of enamel matrix takes place
in two stages, although the time interval
between them is very small.
 In first stage an immediate partial
mineralization in matrix segments and
interprismatic substance.
 Nucleation is initiated by the apatite
crystallites of dentine on which enamel is
laid.

56.  Chemical analysis indicate that the initial
influx may amount to 25% to 30% of total
mineral content.
 Studies have shown that initial mineral is
octacalcium phosphate, it acts as template
for hydroxyapatite. It is unstable and
convert into 2 units of hydroxyapatite

57.  Second stage or maturation is characterized by
gradual completion of mineralization.
 The process of maturation starts from height of
crown and progresses cervically.
 However at each level, maturation begins
at the dentinal end of rod.
 Thus integration of two process: each rod
matures from depth to the surface, and
sequence of maturing rods is from cusp or
incisal edge towards cervical line.

59. Microradiographic view
 Mineralization of enamel originally involve
four stages-
 STAGE 1- 30% mineralized enamel formed
throughout (enamelin forms 8µm highly &
heavily mineralized enamel near DEJ .)

60.  STAGE 2- Increase in mineralization starts
at surface sweeping into deeper layer until
inner 8µm is reached.
 STAGE 3- From inner layer to outer layer. A
15µm surface layer distinguished to be
mineralized slowly.
 STAGE 4- Outer layer of 15µm mineralize
rapidly and heavily so most mineralized