GENERAL CHARACTERS

1-ECTODERMAL TISSUECOVERING THE ANATOMICAL CROWN.

2-HIGHLY MINERALIZED, RISIST MASTICATORY FORCES.

3-ACELLULAR, INERT, NONVITAL AND INSENSITIVE.

4-CANNOT REPALCED OR REGENERATED.

5-PERMEABLE TO IONIC STRUCTURE.

PHYSICAL PROPERTIES

2-THICKNESS

5-PERMEABILITY

1-COLOUR

4-BRITTLNESS

3-HARDNESS

1 - COLOUR

YELLOWIH WHITE TO YELLOWIH WHITE TO GRAYISH WHITEGRAYISH WHITE

DEPENDS ON: 1 -DEGREE OF

CALCIFICATION2 -HOMOGENISITY OF

THE ENAMELSO:

YELLOWISH YELLOWISH TEETH…. TRANSLUCENT E.GRAYISH GRAYISH TEETH …… OPAQUE E .

2 - THICKNESS

-22 – – 2.52.5 mmmm. at the cusps of the molars and premolars.

-Thinning downThinning down to

Almost knife edge at the cervical margin of the tooth

3 – HARDNESS

IT IS THE HARDEST IT IS THE HARDEST CALCIFIED TISSUE IN CALCIFIED TISSUE IN THE BODYTHE BODY DUE TODUE TO:

1 -HIGH CONTENT OF THE MINERAL SALTS

2 -ITS CRYSTALLINE ARRANGEMENT.

-ENAMEL OF THE PERMANENTPERMANENT TEETH E. IS HARDER THAN THAT OF DECIDUOUS ONES’

-ENAMEL ENAMEL MICROHARDNESSMICROHARDNESS

-1 - IS GREATEST AT THE SURFACE AND DECREASED TOWARD

DEJ. 2 - IT IS GREATER AT THE

CUSPS AND INCISAL RIDGE AND DECREASES TOWARD THE CERVICAL LINE.

+

-

+

+

+

-

-

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4 - BRITTLNESS

ITS STRUCTURE AND HARDNESS RENDER IT BRITTLE, SPECILY WHEN IT LOOSES ITS ELASTIC FOUNDATION OF HEALTHY DENTIN

5 -PERMEABILITY

-ENAMEL HAS A CERTAIN CERTAIN DEGREE OF PERMEABILTYDEGREE OF PERMEABILTY DEMONSTRATED BY DYES AND RADIOACTIVE ISOTOPES.

-IT ACTS AS A IT ACTS AS A SEMIPERMEABLE SEMIPERMEABLE MEMBRANEMEMBRANE FOR CERTAIN IONS AND DYES OF SMALL MOLECULAR SIZE THROUGH PORES BETWEEN THE CRYSTALS.

Enamel

•Specific Gravity of enamel is around 2.8

•It shows birefringence

•It is an optical property. It shows two colors when viewed with polarized light

CHEMICAL PROPERTIES

INORGANIC

ORGANIC

INORGANIC ORGANIC

BY WEIGHT

96% 4%

BY VOLUME

EQUAL EQUAL

CHEMICAL PROPERTIES

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INORGANIC MATERIAL 96%

CALISUM PHOSPHATE CRYSTALLINE

(HYDROXY APATITE )

3 Ca3 )PO4(2 . Ca )OH(2

THE SUSCEPTIBILITY OF THESE CRYSTALS TO DISSOLUTION BY ACIDSDISSOLUTION BY ACIDS PROVIDES THE CHEMICAL BASIS FOR THE CARIOUS LESION

THE PROBABILITY OF THE REPLACEMENT OF THE REPLACEMENT OF THE HYDROXYL RAICALHYDROXYL RAICAL WITH VARIOUS IONS (STRONIUM, MAGNESIUM, CARBONATE AND FLOURIDE ) DURING ENAMEL DEVELOPMENT OR IN THE INVIRONMENT OF THE FULLY FORMED ENAMEL GIVES THE BASIS FOR NATIONAL FLUORINATION OF DRINKING WATER OR TOPICAL FLUORIDE APPLICATION TRANSFORMING

HYDROXY APATITEHYDROXY APATITE CRYSTALS TO FLUOROAPATITE FLUOROAPATITE ONES .

3 Ca3 )PO4(2 . Ca )F(2 FOR MORE CARIES RISISTANCE

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ORGANIC MATERIAL 4%)1-2% ORGANIC MATERIAL AND 2-3% WATER(

- IT FORMSIT FORMS A FINE NETWORK BETWEEN THE CRYSTALS, OR COMPRESSSED FORMING AN ENVELOP

SURROUNDING EACH CRYSTAL -ITS CHEMICAL NATUREITS CHEMICAL NATURE HAS NOT YET COMPLETELY

DETERMINED .- NO SPECIFIC PROTEINSNO SPECIFIC PROTEINS HAVE BEEN IDNTIFIED.- AMINO ACIDSAMINO ACIDS PRESENT ARE COLLECTIVELY CALLED ENAMEL PROTEINENAMEL PROTEIN

1 – Amelogenins.: These are present during the enamel formation. These are lost during calcification of enamel

2 – ENAMEL PORTIEN OF HIGH MOLECULAR WEIGHT CALLED ENAMELINENAMELIN :It is present in the enamel matrix and persist in the mature enamel tightly bound to the hydroxy apatite crystals

.

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ENAMEL PROTEIN

) AMINO ACIDS(

DEVELOPING ENAMEL MATRIX

MATURE ENAMEL MATRIX

PROLINE + + + + +

GLUTAMINE + + + +

LEUCINE + + +

GLYCINE + +

HISTIDINE +

GLYCINE + + + + +

GLUTAMINE + + + +

PROLINE + + +

LEUCINE + +

HISTIDINE +

NOTE: THE SELECTIVE REABSORPTION OF THE AMINO ACIDS IS

THE FUNCTION OF THE AMELOBLASTS

HISTOLOGICAL STRUCTURE

ENAMEL PRISM

ENAMEL

DENTIN

ENAMEL PRISM

1-ENAMEL PRISM

2-PRISM SHEATH

3-INTERPRISMATIC

SUBSTANCE

STRUCTURE

HISTOLOGICAL STRUCTURE

HEXAGONAL

OVAL

ROUND

FISH SCALES

KEY HOLE

ENAMEL PRISM

LOWER CENTRAL INCISOR

5 MILLIONS

UPPER FIRST MOLAR

12 MILLIONS

1 - NUMBER

2 - DIRECTION

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ENAMEL PRISM

3 - COURSE

DENTINO-ENAMEL MEMBRANE

STRUCTURELESS ENAMEL

GNARLED ENAMEL

ENAMEL PRISM

4 - DIAMETER

1

2:

3-4 um / 8 um

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BY LIGHT MICROSCOPE

ENAMEL PRISMPRISM

PRISM SHEATH

INTERPRISMATIC SUBSTANCE

CROSS STRIATION

ENAMEL PRISM

BY THE ELECTRON MICROSCOPE

CRYSTALS

CRYSTALS

INTERPRISMATIC SUBSTANCE

PRISM

PRISM SHEATH

Prism sheath

INTERPRISMATIC SUB. WITH HIGHER REFRACTIVE INDEX

PRISM SHEATH

INTERPRISMATIC REGION

PRISM

HEAD

TAIL

HUNTER SCHREGER’S BANDS

Oblique reflected light

Transmitted light

INCREMENTAL LINES

PERIKYMATA

LONG INCREMENTAL LINES

SHORT INCREMENS

CROSS STRIATIONS

BETWEEN SEGMENT OF 4 u LENGTH ,DAILY RATE OF SECRETORY ACTIVITY OF

AMELOBLASTS

11 – – SHORT INCREMENTAL SHORT INCREMENTAL LINESLINES

(CROSS STRIATION)

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2 – LONG INCREMENTAL LINE2 – LONG INCREMENTAL LINE

(INCREMENTAL LINE OF RETZIUS) BROWN STRIA OF RETZIUS

4 DAYS ARE NEEDED FOR THE FORMATION OF THE ENAMEL MATRIX BETWEEN TWO BANDS

33 – – NEONATAL LINENEONATAL LINE

PRENATAL ENAMEL

POSTNATAL ENAMEL

POSTNATAL ENAMEL

PRENATAL ENAMEL

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PRIMARY ENAMEL CUTICLE)Nasmyth’s membrane(

- 0.2 um0.2 um thick.

- Its structurestructure is similar to the basal lamina of the epithelium.

- It is the lastthe last product of the ameloblasts.

THE AMELODENTINAL JUNCTION

ENAMEL

DENTIN

ENAMEL LAMELLAE

TYPE A TYPE B

TYPE C

ENAMEL TUFT

ENAMEL SPINDLES

DENTINAL TUBULES

ENAMEL

DENTIN

SURFACE STRUCTURES

REMEMBER: THAT THERE IS AN INNER STRUCTURELESS ENAMEL

1 – OUTER STRUCTURELESS ENAMEL

30 um thick

2 - PERIKYMATA

PARALLEL PARALLEL TO EACH OTHER AND TO C.E.J.

CONTINUOUS AROUND THE TOOTH.

30/ mm30/ mm – AT THE REGION OF C.E.J.

10/ mm10/ mm – NEAR TO THE OCCLUSAL OR INCISAL EDGES

3 - ROD ENDS

SHALLOWERSHALLOWER CERVICALLY

DEEPERDEEPER OCCLUSALLY

4 - CRACKS

ENAMEL LAMELLA

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5 - AFIBRILLAR CEMENTUM

ENAMEL

DE

NT

IN

CEMENTUM

LIFE HISTORY OF THE AMELOBLASTS

1 - MORPHOGENIC2 - ORGANIZING

DEAL WITH INNER DENTAL

EPITHELIUM

7 STAGES

3 – FORMATIVE4 – TRANSITIONAL

5 - MATURATIVE

FUNCTIONS OF DIFFERENTIATED AMELOBLASTS

6 – PROTECTIVE7 - DESMOLYTIC

FUNCTIONS OF THE REDUCED

ENAMEL EPITHELIUM

REDUCED ENAMEL EPITHELIUM

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Before ameloblasts differentiation

A – MORPHOGENIC STAGE

INNER DENTAL EPITHELIUM

CELL FREE ZONE

DENTAL PAPILLA

BASEMENT MEMBRA

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Before ameloblasts differentiation

A – MORPHOGENIC STAGE

Oval nucleus

Short columner

Golgi apparatus

Centriol

Mitochondria

PROXIMAL END

DISTAL END

BASEMENT MEMBRANE

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During ameloblasts differentiation

A – MORPHOGENIC STAGE

NUCLEUS

GOLGI APP.

CENTRIOL

MITOCHONDRIA

PROXIMAL TERMINAL BARS

BASEMENT MEMBRANE

PROXIMAL END

DISTAL END

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B – ORGANIZING STAGEINNER DENTAL

EPITHELIUM

ODONTOBLASTS

INNER DENTAL EPITHELIUM

Cell free zone disappears

ODONTOBLASTS

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B – ORGANIZING STAGE

Centrioles

Golgi apparatus

Mitochondria

SO DURING THIS STAGE THE FOLLOWIONG OCCURE:

1 - REVERSAL OF THE FUNCTIONAL POLARITY OF THE I.D.E...

2 –HISTO-DIFFERENTIATION OF THE ODONTOBLASTS ) INDUCTION(.

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C – FORMATIVE STAGE

DENTIN

AMELOBLASTS

G.AG.A.

R.E.RR.E.R..

MM

DISTAL TERMINAL BARS

TOME’S PROCESS

PROXIMAL TERMINAL BARS

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D – TRANSITIONAL STAGE

PRISMLESS ENAMEL

1 – REDUCTIONREDUCTION IN THE HIGHT.

2 – DECREASEDECREASE IN IN ITS VOLUM AND ORGANELLE CONTENT

3 – WITHDRAWAL OF TOME’S ROCESS.

1 – REDUCTIONREDUCTION IN THE HIGHT.

2 – DECREASEDECREASE IN IN ITS VOLUM AND ORGANELLE CONTENT

3 – WITHDRAWAL OF TOME’S ROCESS.

E – MATURATIVE STAGE

AUTOPHAGIC VACUOLES

RUFFLED ENDED AMELOBLASTSMOOTH ENDED AMELOBLAST

CYTOPLASMIC VACUOLES

MM

F – PROTECTIVE AND DESMOLYTIC STAGES

REDUCED ENAMEL EPITHELIUM

1 – PROTECTIVE.

2 - DESMOLYTIC

SUMMARY

De

ntin

Aprismatic enamel

Aprismatic enamel

Prismatic enamel

Ameloblast without

Tome’s process

Ameloblast without

Tome’s process

Ameloblast with

Tome’s process

Late organizing stage

Formative stage Transitional stage

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THE BEGINNING OF MINERALIZATION OF THE ENAMEL MATRIX DOES NOT AWAIT THE

COMPLETION OF ITS FORMATION.

AMELOGENESISAMELOGENESIS

1 - FORMATION 1 - FORMATION OF ENAMEL OF ENAMEL

MATRIXMATRIX

2 - MATURATION 2 - MATURATION OF ENAMELOF ENAMEL

FORMATION OF ENAMEL MATRIX

STRATUM INTERMEDIUM

AMELOBLASTS

ENAMEL MATRIX )DENTINOENAMEL

MEMBRANE (

MANTLE DENTIN

D . J .C.

STIPPLED MATERIAL/OR ENAMEL

NO CLEAR CUT BAND OF ORGANIC MATRIX

25 – 30 % OF THE TOTAL MINERAL CONTENT

De

ntin

Aprismatic enamel

Aprismatic enamel

Prismatic Enamel

Ameloblast without

Tome’s process

Ameloblast without

Tome’s process

Ameloblast with

Tome’s process

Late organizing stage

Formative stage Transitional stage

Prism

Tome’s process

Prism sheath

Interprismatic

substance

Cross

straiation

MORE DETAILS ABOUT THE MODE OF FORMATION AND LOCATION OF THE PRISM, INTERPRISMATIC

SUBSTANCE, PRISM SHEATH AND CROSS STRIATION

ASG

Head / or

Prism

Tail / or

Interprismatic

substance

Tome’s process

Next

1 MORE DETAILS ABOUT THE PROCESS OF SECRETION OF BOTH THE PROTEINS AND THE CRYSTALLITES FROM THE TOME’S PROCESS

ASG

Tome’s process

Next

Tail

Head

2

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Tome’s process

Next

Tail

Head

3

ASG

Tome’s process

Tail

Head

4

Tail

Head

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2 - MATURATION OF ENAMEL

ONCE THE FULL THICHNESS OF ENAMEL MATRIX IS FORMED

MATURATION BEGINS

DURING MATURATION THE FOLLOWING

CHANGES OCCURE

1 - Quantitative And Qualitative Changes In The Organic Component.

2 - 90 % Of Protein And Water Reabsorbed.

3 – Maturation Is Gradually Completed Up To 96% Of The Total Weight Of Enamel ))Primary Primary Maturation(Maturation(

4 – Rapid Influx Of Calcium And Phosphate Ions Already Secreted With The Enamel Matrix.

5 – Increase In Size Of The Crystals By Fusion Of Crystallites ) 1240 Crystal / Um Before And 560 Crystal / Um After Maturation (.

5 – – Directions Of Maturation …)next slide (– Directions Of Maturation …)next slide (

6 - 6 - Secondary Maturation..Secondary Maturation..

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DIRECTIONS OF MATURATION

ENAMEL

DENTIN

PREDENTIN

ENAMEL

DENTIN

PREDENTIN

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SECONDARY MATURATION

MATURATION CONTINUES AFTER ERUPTION OF

THE TEETH THROUGH DEPOSITION OF IONS FROM THE SALIVA.

AGE CHANGES

1 - ATTRITION

ATTRITION

• DEFINITION.• DIFFERENCE BETWEEN D.T. AND P.T.• CLINICALY: OCCLUSAL AND PROXIMAL.• SEX DIFFERENCE.• TYPE OF DIET.• OCCUPATIONAL HABITS.• SEVERE ATTRITION.• MICROSCOPICALLY.

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2 - PERMEABILITY

Main pathRecently

Erupted teeth

Old enamel

2 - PERMEABILITY

• IONIC EXCHANGE BETWEEN THE ENAMEL AND THE SURROUNDING SALIVA.

• SECONDARY MATURATION.• INCREASE NITROGEN AND FLUORIDE.• RESISTANCE TO DECAY IS INCREASED.• TOOTH MAY BECOME DARKER IN COLOUR

)THE EFFECT OF THE DAYSTUFFS STAINS(

THANK YOUAND

GOOD LUCK

THANK YOUAND

GOOD LUCK