2- enamel (mahmoud bakr)(1)
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Griffith University Oral Biology 2 1009 DOH
Enamel
Dr. Mahmoud Bakr
Lecturer in General Dental Practice
B.D.S, M.D.S (Cairo University), ADC (Australia)
Member of the Australian Dental Association (ADA),
the Australian Biology Institute Inc. (ABI) and the
Egyptian Dental Union (EDU)
Learning objectives: After completing this lecture you should be able to:
1- Name, classify, identify and describe the
structure and function of the components of
Enamel.
2- Describe age related changes to Enamel and their
effects.
3- By observing the histological details of cells and
tissues, you should be able to use a microscope to
identify different histological structures of
Enamel and understand the histological processes
involved in preparing slides.
• All Microscopic images are taken from the
Digital Library of the Oral Biology
Department (Cairo University).
INTRODUCTION
ENAMEL
-Makes up the outside layer of anatomical crown of a tooth
-Covers and protects the dentin of the crown
-Firmly attached to the underlying dentin at the dentinoenamel junction and meets the cementum at the cementoenamel junction
-The hardest and most mineralized substance of the body
-Has no way to regenerate itself
2-THICKNESS
5-PERMEABILITY
1-COLOUR
4-BRITTLNESS
3-HARDNESS
PHYSICAL PROPERTEIS
1- Colour: 1 - COLOUR
YELLOWISH WHITE TO GRAYISH WHITE
: DEPENDS ON
1- DEGREE OF CALCIFICATION
2- HOMOGENOUSITY OF THE ENAMEL CRYSTALS.
SO:
TRANSLUCENT E. YELLOWISH TEETH
OPAQUE E.
GREYISH TEETH
2-Thickness 2 - THICKNESS
- 2 – 2.5 mm. at the cusp tips.
- Thinning down to
Feather edge at the cervical line of the tooth
2 - THICKNESS
Thin enamel is
present at the
bottom of the pits
and fissures of the
crown surface
dentin
enamel
3 – HARDNESS
IT IS THE HARDEST
CALCIFIED TISSUE IN THE
BODY
DUE TO:
1- HIGH CONTENT OF THE
MINERAL SALTS
2- ITS CRYSTALLINE
ARRANGEMENT.
- ENAMEL OF THE
PERMANENT TEETH
IS HARDER THAN
THAT OF DECIDUOUS
ONES
+
-
+
+
3 – HARDNESS
-1 - IS GREATEST AT THE
AND SURFACE
DECREASED TOWARD
DEJ.
2 - IT IS GREATER AT THE
AND INCISAL CUSPS
RIDGE AND DECREASES
CERVICALTOWARD THE
LINE.
3- It is the hardest tissue of
the body
+
-
+
+
+
-
-
4- Brittleness: 4 - BRITTLENESS
-Very brittle due to large amount of minerals
-Dentin, which is less mineralized and less brittle, compensates
for enamel and is necessary as a support for enamel
-If this supportive layer of dentin is destroyed by caries or
improper cavity preparation, the unsupported enamel fractures
5- PERMEABILITY - IT ACTS AS A SEMIPERMEABLE MEMBRANE FOR CERTAIN IONS THROUGH PORES BETWEEN THE CRYSTALS.
-PER. IS MAINLY FROM
SALIVA TO OUTER
LAYER OF ENAMEL, BUT
LESS FROM THE PULP
TO THE INNER ENAMEL
LAYER ACROSS THE
DENTIN.
CHEMICAL PROPERTIES
water organic inorg
2% 1-2% 95-96% By
weight
10-12% 88-90% By
volume
INORGANIC
ORGANIC
a- Inorganic material of enamel:
CALCIUM PHOSPHATE
( HYDROXY APATITE)
CRYSTALS
3 Ca3 (PO4)2 . Ca (OH)2
-Most crystals are regularly
hexagonal in cross section.
(VERY LARGE) -
-They are 70 nm. in width,
25 nm. in thickness
length may reach to 0.1 micron
INORGANIC MATERIAL 96 %
Various ions if present during enamel formation or in
the environment of fully formed enamel may replace
the different ions of the molecule
. Hydroxyapatite is converted to fluoroapatite
when fluoride ion replaces the hydroxyl ion
3 Ca3 (PO4)2 . Ca (F)2
Fluorapatite is 20%less
soluble than
hydroxyapatite
it is much less
susceptible to
demineralization.
-Fluoridation of drinking
water.
HISTOLOGICAL STRUCTURE
•THERE ARE TWO TYPES OF
PREPARATIONS FOR
HISTOLOGICAL STUDY OF
HARD TISSUES :
•1-DECALCIFIED SECTIONS:
•2-GROUND SECTION
•More calcified more
translucent
As Enamel contains 96%
inorganic material so it cannot
be seen in decalcified sections
It can only be studied in Ground
sections
ENAMEL ROD
The basic structural unit of enamel
May be hexagonal and prism-like in cross
section
Rods do not have a fixed regular
geometrical outline and the term enamel
rod is preferred in this text
ENAMEL ROD
LOWER CENTRAL INCISOR
5 MILLIONS
UPPER FIRST MOLAR
12 MILLIONS
1 - NUMBER
2 - DIRECTION
DECIDUOUS PERMANENT
ENAMEL ROD
3–SIZE
3-4 um in diameter
Up to 2.5 mm. in length
ENAMEL ROD
4- COURSE
STRUCTURELESS
ENAMEL GNARLED
ENAMEL
Wavy course except
near the incisal edge
or cusp tips where
enamel rods have a
more complex
course (Gnarled
Enamel) to withstand
masticatory forces
Gnarled Enamel
Histological structure of enamel rod
LS.
TS
ENAMEL ROD
LONGITUDINAL SECTION
ENAMEL ROD ROD
ROD
SHEATH
INTERROD
REGION
CROSS
STRIATION
Cross section of enamel rod
Key hole pattern Fish scales pattern
Enamel rod
ENAMEL ROD
CRYSTALS
CRYSTALS
INTERROD
SUBSTANCE
ROD SHEATH
HEAD
(occlusally)
TAIL
(Cervically)
HUNTER SCHREGER’S BANDS
It is an optical phenomenon
can be seen in: 1-LONG.GROUND SEC. IN ENAMEL
2-OBLIQUE REFLECTED LIGHT
It is due to the wavy course of Enamel rods
HUNTER SCHREGER’S BANDS
Life history of ameloblasts
1-Differentiating
stage
(presecretory).
2- Secretory stage.
3- Transitional stage.
4- Maturative stage.
5- Protective stage.
6- Desmolytic stage
LIFE HISTORY OF THE
AMELOBLASTS
1-DIFFERENTIATING
DEAL WITH INNER
DENTAL
EPITHELIUM
6 STAGES
LIFE HISTORY OF THE
AMELOBLASTS 6 STAGES
2– SECRETORY
3– TRANSITIONAL
4- MATURATIVE
FUNCTIONS OF
AMELOBLASTS
LIFE HISTORY OF THE
AMELOBLASTS 6 STAGES
5 – PROTECTIVE
6 -- DESMOLYTIC
REDUCED DENTAL EPITHELIUM
REDUCED
DENTAL
EPITHELIUM
Why life history not life cycle????
Because Ameloblasts are lost in Reduced Dental Epithelium after complete crown formation.
We don’t have Ameloblasts in our teeth it’s HISTORY.
It’s not a repetitive cycle.
Ameloblasts differentiate from I.E.E
In Early Bell Stage I.E.E cells are separated from Dental Papilla by Cell free zone
I.E.E cells elongate on the expense of Cell free zone and becomes in contact with Dental Papilla
Now they are called Preameloblasts
Preameloblasts induce the formation of Odontoblasts by a process called Induction
1- Differentiating stage:
ASG
Before ameloblasts
differentiation
1- Differentiating stage:
INNER DENTAL
EPITHELIUM
CELL FREE
ZONE
DENTAL
PAPILLA
BASEMENT
MEMBRA
Histological structure of
Preameloblasts
• As a preparatory step for Enamel matrix
secretion Polarization or Reverse of
Functional Polarity occurs:
Nucleus and Mitochondria move towards the
proximal end of the cell
RER, Golgi apparatus and centrioles move
towards the distal end of the cell.
ASG
Before ameloblasts
differentiation
1- Differentiating stage:
Oval nucleus
Short columnar
Golgi apparatus
Centriol
Mitochondria
DISTAL END
BASEMENT MEMBRANE
ASG
1- Differentiating stage:
NUCLEUS
GOLGI APP.
CENTRIOL
MITOCHONDRIA
BASEMENT
MEMBRANE
DISTAL
END
NUCLEUS
GOLGI APP.
CENTRIOL
MITOCHONDRIA
PROXIMAL
JUNCTIONAL
COMPLEX
Basal lamina
PROXIMAL
END
DISTAL
END
ASG
1- Differentiating stage:
Centrioles
Golgi apparatus
Mitochondria
SO DURING THIS
STAGE THE
FOLLOWIONG
OCCURE:
1 - REVERSAL OF
THE FUNCTIONAL
POLARITY OF THE
I.E.E...
2 –HISTO-
DIFFERENTIATION
OF THE
ODONTOBLASTS
( INDUCTION).
ASG
1- Differentiating stage:
INNER DENTAL
EPITHELIUM
(Preameloblasts)
ODONTOBLASTS
During this stage Preameloblasts change
into Ameloblasts by a process called
Reciprocal Induction by signals from
Odontoblasts
Remember: Ameloblasts secret Enamel
matrix not Enamel
(only the organic component)
2- Secretory stage:
Histological structure of
Ameloblasts (ultrastructure)
As formative (Blast) cells Ameloblasts have all the criteria of protein forming cells (Blast cells):
1- Large open face (lightly stained) nucleus.
2- Abundant (rich) cytoplasm.
3- Increase in Mitochondria
4- Increase in Golgi apparatus
5- Increase in RER
6- Increase in Alkaline Phosphatase activity
7- Presence of secretory vesicles
Tomes’ Process
Is a conical process that develops from the distal
end of Ameloblasts during secretory stage.
It is responsible for the different orientation of
crystals in the Enamel rod and Interod
substance.
It gives the cells Picket fence appearance
Note: Tomes’ process not Tome’s process
2-SECRETORY STAGE
G.A.
R.E.R.
M
DISTAL
TERMINAL BARS
TOME’S PROCESS
PROXIMAL
TERMINAL BARS
Picket fence appearance
E. matrix
3 – Transitional Stage:
BASAL LAMINA
1 – REDUCTION IN HEIGHT.
2 – DECREASE IN ITS VOLUME
AND ORGANELLE CONTENT
3 – WITHDRAWAL OF TOMES,
PROCESS.
4-DECREASE IN OVERALL
CELL NO.
All these changes are related
to shift of function from
Protein synthesis (secretory
stage) to ion transport
(maturative stage).
There are two types of Ameloblasts in this
stage:
A- Ruffled ended Ameloblasts (80%)
B- Smooth ended Ameloblasts (20%)
4–Maturative stage
4–Maturative stage
4 – MATURATIVE STAGE
AUTOPHAGIC
VACUOLES
RUFFLED ENDED AMELOBLAST SMOOTH ENDED AMELOBLAST
CYTOPLASMIC
VACUOLES
M
MATURATIVE AMELOBLAST
RUFFLED
ENDED
SMOOTH
ENDED
Leaky
proximal
junction
Tight
distal
junction
Tight
proximal
junction
Leaky
distal
junction
•Influx of mineral ions into the present partially mineralized matrix occurs in relation to ruffled- ended cells
•Withdrawal of organic matrix from the maturing enamel occur mainly in the ruffled- ended cells as well as through passing between the leaky distal junctions of the smooth-ended cells
After complete Enamel matrix
formation and maturation
Ameloblasts become squeezed
as a layer of Reduced Enamel
Epithelium which protects Enamel
from resorption by cells from
Dental Sac.
5– Protective stage:
5– PROTECTIVE STAGE
REDUCED DENTAL
EPITHELIUM
PRIMARY ENAMEL CUTICLE
Reduced Enamel Epithelium (with
Ameloblasts being a part of it) secrets
desmolytic enzymes for elimination of
Dental sac and allowing fusion between
Reduced Enamel Epithelium and Oral
Epithelium.
This allows eruption of the tooth without
bleeding.
It is called Primary Enamel Cuticle which is
the last product of Ameloblasts.
6– DESMOLYTIC STAGE
ENAMEL
REDUCED DENTAL
EPITHELIUM
TOOTH ERUPTION
GINGIVAL
EPITHELIUM
still fusing with
E.CUTICLE
will wear away
THE BEGINNING OF MINERALIZATION OF THE
ENAMEL MATRIX DOES NOT AWAIT THE
COMPLETION OF ITS FORMATION.
AMELOGENESIS
A–SECRETORY
PHASE
B- MATURATION
PHASE
A-- Secretory phase:
Beginning of secretion End of secretion
STIPPLED MATERIAL OF ENAMEL
1- Stippled material secretion:
STRATUM INTERMEDIUM
AMELOBLASTS
ENAMEL MATRIX
MANTLE DENTIN
Secretory ameloblast
The first hydroxyapatite crystals formed interdigitate with the crystals of dentin.
NO CLEAR CUT BAND OF ORGANIC MATRIX
2- Initial rodless (aprismatic) enamel layer:
Stippled material secretion
INNER DENTAL
EPITHELIUM
(PREAMELOBLAST)
3-Rod (prismatic) enamel layer:
ROD
ROD
4- -Final rodless (aprismatic)
enamel layer
•The ameloblasts
become shorter and
Tomes' processes are
lost
End of secretory ameloblast
Disturbances during the secretory stage of
amelogenesis result in pathologically thin or
hypoplastic enamel
Den
tin
Rodless
enamel Rodless
enamel
Rod
(Prismatic)
Enamel
Ameloblast
without
Tomes
process
ameloblast
without
Tomes
process
Ameloblast
with
Tomes
process
Secretory stage
End of secretory
stage
B-Maturation Phase
1- Primary maturation
2- Secondary maturation
3- Tertiary (post-eruptive) maturation
1- Primary maturation
•The first secreted
enamel matrix
contains 20-30 % of
the mineral content
•The crystals are thin
and can grow
primarily in length
2- Secondary maturation •-A selective removal of enamel
proteins and water occurs resulting in
a change in the ratio of the proteins of
the newly secreted enamel matrix and
the final matrix of mature enamel
•-Amelogenins and ameloblastins are
removed leaving enamelins and
tuftelin in the mature enamel .
•--In the same time the ameloblasts
transport mineral ions into this
partially mineralized enamel matrix
which cause growth of the crystals in
width and thickness
•The enamel crystals never fuse
•-
Direction of maturation
3- Tertiary maturation
•After tooth eruption
and exposure of
enamel to saliva in
the oral cavity,
precipitation of certain
ions on the outermost
enamel layer occurs ions
Defective maturation
hypomaturative soft enamel
1- Incremental lines of Enamel:
a- Cross striations
b- Incremental lines of Retzius
c- Neonatal line
2- Enamel Tufts
3- Enamel Lamellae (Type A)
4- DEJ
Hypocalcified structures of
Enamel
INCREMENTAL LINES OF
ENAMEL
They are formed as a result of the
rhythmic manner of Enamel (periods
of activity alternating with periods of
rest)
Enamel is formed increment by
increment
They are formed as a result of the daily rest
of Ameloblasts
Ameloblasts form 4 microns of Enamel then
rest so the distance between cross
striations is 4 microns
1 – SHORT INCREMENTAL
LINES
( CROSS STRIATION )
BETWEEN SEGMENT OF 2.5-6 u LENGTH,
DAILY RATE OF SECRETORY ACTIVITY OF
AMELOBLASTS
1 – SHORT INCREMENTAL
LINES
( CROSS STRIATION )
2 – LONG INCREMENTAL LINE
( INCREMENTAL LINE OF RETZIUS )
BROWN STRIA OF RETZIUS
They are formed due to the
weekly rest of Ameloblasts
The distance between them is
16 microns
When viewed microscopically
in cross-section, they
appear as concentric rings.
In a longitudinal section, they
appear as a series of dark
bands .
7 DAYS ARE NEEDED FOR THE FORMATION OF THE
ENAMEL MATRIX BETWEEN TWO BANDS
It an accentuated incremental line that separates between Enamel formed before birth and that formed after birth.
It is only seen in Deciduous teeth and Permanent First Molars (Why?)
As the rest of Permanent teeth are developed after birth.
The quality of Prenatal Enamel is better than Postnatal Enamel (Why?)
Due to constant nutrition and more protected environment inside the uterus .
3 – NEONATAL LINE
3 – NEONATAL LINE
PRENATAL
ENAMEL
POSTNATAL
ENAMEL
POSTNATAL
ENAMEL
PRENATAL
ENAMEL
Enamel of lower D formed at birth
It appears only in T.S ground section of
Enamel as a result of different crystal
orientation (The function of Tomes’
process).
It starts from DEJ and extends to 1/3 or 1/5
of the thickness of Enamel.
It appears as a tuft of grass.
ENAMEL TUFT
ENAMEL TUFT
ENAMEL TUFT
It is a scalloped line between Enamel in dentin.
It is smooth sometimes in Deciduous teeth.
The convexities are always towards Dentin.
It is hypocalcified due to high organic content of Enamel and Dentin in this area.
The bond between Enamel and Dentin is organic not mechanical.
THE DENTINOENAMEL
JUNCTION
THE DENTINOENAMEL
JUNCTION
THE DENTINOENAMEL
JUNCTION
ENAMEL
DENTIN
It extends from the outer surface of Enamel
to the DEJ and may extend to Dentin.
Types of Enamel lamellae:
A- Developmental (type A)
B- Non Developmental (type B,C)
LAMELLAEENAMEL
LAMELLAEENAMEL
1- Developmental (true lamellae )
(Type A lamella):
Occurs during amelogenesis
Hypomineralized structures
Never extend to dentin
2-Non developmental
(false lamellae or cracks ) :
Unmineralized areas
that occur after
amelogenesis is
completed
They are divided into:
i-Type B lamella A crack occurs in the enamel after its complete formation but before the tooth eruption
ii- Type C lamella
A crack occurs in the enamel after the tooth eruption
iii -An accidental crack
during section preparation
Uncalcified structures
1- Non-Developmental lamellae
(Type C)
2- Enamel spindle
It is actually an odontoblastic process that
crosses the DEJ to reach Enamel.
It usually found under the incisal edge or
cusp tips.
It can be seen both in L.S. and T.S.
ENAMEL SPINDLES
ENAMEL SPINDLES
ENAMEL SPINDLES
ODONTOBLASTIC
PROCESS
ENAMEL
DENTIN
SURFACE STRUCTURES OF
ENAMEL
REMEMBER: THAT THERE IS AN INNER STRUCTURELESS
ENAMEL
1 – OUTER STRUCTURELESS ENAMEL
20-70 um thick
2- PERIKYMATA
PARALLEL TO EACH OTHER
AND TO CERVICAL LINE
CONTINUOUS AROUND THE
TOOTH.
NUMEROUS AT THE
CERVICAL REGION
VERY FEW NEAR THE
OCCLUSAL OR INCISAL
EDGES
3 - ROD END MARKING
SHALLOW
CERVICALLY
DEEPER
OCCLUSALLY
4 - CRACKS
ENAMEL
LAMELLA
5 - AFIBRILLAR CEMENTUM
ENAMEL
DE
NT
IN
CEMENTUM
1-ATTRITION
• Definition.
• Wear rate 8 mm /year
• Parafunctional
movements, as found in
bruxism
• Wear polished facets
• Nonbacterial processes
of enamel destruction
• 1-abrasion
• 2-erosion .
2- COLOUR
• IONIC EXCHANGE BETWEEN THE
ENAMEL AND THE SURROUNDING
SALIVA. (TERTIARY MATURATION.)
• INCREASE NITROGEN AND FLUORIDE.
• RESISTANCE TO DECAY IS INCREASED.
3- MODIFICATION IN
SURFACE LAYER:
ASG
4- PERMEABILITY
Main path Recently
Erupted teeth
Old enamel
Permeability of Enamel decreases
by age, but remains only in the
most superficial layer.
Permeability of Enamel decreases by
age, but remains only in the most
superficial layer.
Clinical Considerations
1- Acid-etching
A,B :itched rods
C: non itched rods
Type 1 is a pattern where predominantly the
enamel rods are dissolved.
Type 2 is a pattern where predominantly the
interrod enamel is dissolved
Type 3 is a pattern where there is no evidence left
of any enamel rods.
2-Tooth Whitening
Can be done by removal of the surface discolored
layer of Enamel either :
a- Mechanically (Prophylactic paste and abrasion)
b- Chemically by using bleaching agents such as:
Sodium perborate and sodium hypochlorite
3- Amelogenesis Imperfecta
It is a congenital defect that occurs during Enamel formation.
It is either:
a- Enamel Hypoplasia: it is a defect in the quantity of Enamel matrix. (disorder during the secretory phase of Amelogenesis)
b- Enamel Hypocalcification: it is a defect in the quality of the calcified Enamel matrix. (disorder during the maturation phase of Amelogenesis)
What Enamel structures can you
see in this picture?
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