Physical propertiesPhysical properties

Chemical CompositionChemical CompositionInorganic phase

Organic phase

Development (genesis):Development (genesis):Forming cells: (life history)

Matrix formation (protein

synthesis)

Calcification (mineralization)

Ultra-structure Ultra-structure Structural unit-Regional

variation

Incremental linesIncremental linesAge changes

Clinical consideration

Histological Study of Hard Dental TissuesHistological Study of Hard Dental Tissues::

ENAMELENAMEL

* PHYSICAL PROPERTIES:

COLOR

THICKNESS

HARDNESS

BRITTLENESS

PERMEABILITY

The hardest calcified tissue in the bodyThe hardest calcified tissue in the bodyforms the protective covering of the crownforms the protective covering of the crown

11 - - COLOURCOLOUR

YELLOWIH WHITE YELLOWIH WHITE TO GRAYISH TO GRAYISH

WHITEWHITEDepends onDepends on: :

11 - -Degree of Degree of calcificationcalcification

22 - -Homogenisity of Homogenisity of the enamelthe enamel

YELLOWISH teeth….YELLOWISH teeth…. Translucent Translucent enamelenamel

GRAYISH teethGRAYISH teeth.…….…… Opaque enamelOpaque enamel

22 - - THICKNESSTHICKNESS

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

- -Thinning downThinning down toto almost knife almost knife edge at the edge at the cervical margin cervical margin of the toothof the tooth

33 – – HARDNESSHARDNESS

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.

+

-

+

+

+

-

-

ASG

44 - - BRITTLNESSBRITTLNESS

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

55 - -PERMEABILITYPERMEABILITY--ENAMEL HAS A ENAMEL HAS A CERTAIN CERTAIN

DEGREE OF PERMEABILTYDEGREE OF PERMEABILTY DEMONSTRATED BY DYES DEMONSTRATED BY DYES AND RADIOACTIVE AND RADIOACTIVE ISOTOPESISOTOPES..

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

-PER. IS MAINLYMAINLY FROM SALIVA TO OUTER LAYER OF ENAMEL, BUT LESS FROM THE PULP TO THE INNER ENAMEL LAYER ACROSS THE DENTIN.

CHEMICAL COMPOSITIONCHEMICAL COMPOSITION::

CRYSTALLINE CALCIUM PHOSPHATE

“HYDROXYAPATITE” Ca 10(PO4)6 (OH)2

96%96%

By weight

4%4%

AMELOGENINS ENAMELINS and Water

INORGANICINORGANIC CONTENTCONTENT

ORGANIC ORGANIC CONTENTCONTENT

Methods of StudyingMethods of Studying ” ”hard tissueshard tissues””

GROUND SECTIONGROUND SECTION DECALCIFIED SECTIONDECALCIFIED SECTION

ENAMEL ROD ENAMEL ROD oror PRISM PRISM

NUMBER:

DIRECTION:

COURSE:

DIAMETER:

Cross Section:

STRUCTURAL UNITSTRUCTURAL UNIT::

Longitudinal section:

ENAMEL PRISMENAMEL PRISMLOWER CENTRAL INCISOR

5 MILLIONS

UPPER FIRST MOLAR

12 MILLIONS

1 - NUMBER

2 - DIRECTION

D

Dp

ENAMEL PRISMENAMEL PRISM

3 - COURSE

DENTINO-ENAMEL MEMBRANE

STRUCTURELESS ENAMEL

Wavy Course of Enamel Rods

GNARLED ENAMELGNARLED ENAMEL

longitudinal Section:

Cross Section: Hexagonal, fish scales, keyhole pattern

Ameloblast

Tomes process

SUBMICROSCOPIC STRUCTURE SUBMICROSCOPIC STRUCTURE OF ENAMEL RODOF ENAMEL ROD

Enamel rod

T.S

L.S

T.S

L.S

Key holeKey hole analogyanalogy

Key-hole Key-hole PatternPatternEnamel

prismInterprismatic

regionPrism sheath

Head of keyhole“core” “Tail region”

Boundary around” the head

HUNTER-SCHREGER BANDSHUNTER-SCHREGER BANDS(optical phenomenon) dark and light (optical phenomenon) dark and light bandsbands

HISTOLOGICAL STRUCTURES OF HISTOLOGICAL STRUCTURES OF ENAMEL ENAMEL

Incremental linesIncremental lines Enamel lamellaeEnamel lamellae Enamel tuftsEnamel tufts Enamel spindleEnamel spindle Dentinoenamel junctionDentinoenamel junction

STRUCTURAL FEATURES OF STRUCTURAL FEATURES OF ENAMELENAMEL

CROSS STRAIATIONS (short increment)

INCREMENTAL LINES OF RETZIUS

( long increment)

Incremental lines:

INCREMENTAL LINES OF RETZIUS ( long increment)

Enamel Rods

Cross Striations

Incremental lines of Retzius

• NEONATAL LINENEONATAL LINE

PRENATAL ENAMEL

Before birth

POSTNATAL ENAMEL

After birth

POSTNATAL ENAMEL

PRENATAL ENAMEL

dentin

d

Incremental lines of RetziusIncremental lines of RetziusSurface manifestation : PerikymataSurface manifestation : Perikymata

2- ENAMEL TUFTS

Structural features in EnamelStructural features in Enamel

1- ENAMEL LAMELLAE

3- Dentino - Enamel Junction

Enamel Enamel lamellaelamellae

Enamel lamellaeEnamel lamellae

In enamel only

Extending in enamel and dentin

Enamel Enamel SpindlesSpindles

THE AMELODENTINAL THE AMELODENTINAL JUNCTIONJUNCTION

ENAMEL

DENTIN

ASG

PRIMARY ENAMEL PRIMARY ENAMEL CUTICLECUTICLE(Nasmyth’s membrane)(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.

PRIMARY ENAMEL CUTICLE

1ry e.cuticle

Longitudinal Ground Section

Transverse Ground Section

HUNTER-SCHREGER BANDSHUNTER-SCHREGER BANDS(optical phenomenon) dark and light (optical phenomenon) dark and light bandsbands

Observed in L.s ground section under reflected light

* OUTER STRUCTURELESS ENAMEL

*PERIKYMATA

*ENAMEL ROD ENDS

* CRACKs

*Afibrillar cementum

SURFACE STRUCTURES OF ENAMEL

SURFACE STRUCTURESSURFACE STRUCTURES

REMEMBER: THAT THERE IS AN INNER STRUCTURELESS ENAMEL

1 – OUTER STRUCTURELESS ENAMEL

30 um thick

Perikymata Perikymata Surface manifestation of Incremental lines Surface manifestation of Incremental lines

of Retziusof Retzius

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

Enamel Rod Ends

SHALLOWERSHALLOWER CERVICALLYDEEPERDEEPER OCCLUSALLY

CRACKs

AFIBRILLAR AFIBRILLAR CEMENTUMCEMENTUM

E

C

SALIVARY PELLICLE

Age changes of EnamelAge changes of Enamel

AttritionAttrition Decreased PermeabilityDecreased Permeability Increased Hardness (ionic Increased Hardness (ionic

exchange)exchange) Color changesColor changes

AttritionAttrition

Dentin

ASG

22 - - PERMEABILITYPERMEABILITY

Main pathRecently

Erupted teeth

Old enamel