2- Enamel (Mahmoud Bakr)(1)

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

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?