UP TO DATE IN

ORAL BIOLOGY AND EMBRYOLOGY

Prof. Dr. Nahed A. KhalilHead of Oral Biology Department

&Contributing Staff Members

Faculty of Oral &Dental Medicine Cairo University

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::1 -

COLOURYELLOWISH WHITE TO YELLOWISH WHITE TO GRAYISH WHITE GRAYISH WHITE

DEPENDS ON :

1- DEGREE OF CALCIFICATION

2- HOMOGENISITY OF THE ENAMEL CRYSTALS.

SO:TRANSLUCENT E. YELLOWISHYELLOWISH TEETH

OPAQUE E. GRAYISH GRAYISH TEETH

22--ThicknessThickness 2 - THICKNESS

- 22 – – 2.52.5 mmmm. at the cusp tips.

- Thinning downThinning down to featheredge at the cervical l ine of the tooth

3 – HARDNESS

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

1- HIGH CONTENT OF THE MINERAL SALTS

2- ITS CRYSTALLINE ARRANGEMENT.

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

-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.

+

-

++

+

-

-

44- - Britt lenessBritt leness:: 4 - BRITTLENESS-Very britt le due to large amount of minerals

-Dentin, which is less mineralized and less britt le, 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

Enamel can act as a semipermeable membraneThe main pathway is from the saliva to the outer layer of enamel

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

GROUND SECTIONGROUND SECTION DECALCIFIED SECTIONDECALCIFIED SECTION

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

unit structure

of enamel

Enamel Rod (prism(

ENAMEL ENAMEL RODROD

LOWER CENTRAL

INCISOR 5 MILLIONSUPPER FIRST

MOLAR 12 MILLIONS

1 - NUMBER

2 - DIRECTION

DECIDUOUS

PERMANENT

ENAMEL ENAMEL RODROD

3–SIZE

3-4 um in diameter Up to 2.5 mm. in

length

Wavy Course of Enamel Rods

Cross Section : Hexagonal, f ish scales, keyhole pattern

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

Hunter Schreger bands

Note that Hunter Schreger bandsStart from the ADJ an end before reaching the outer surface of enamel

HISTOLOGICAL STRUCTURES OF HISTOLOGICAL STRUCTURES OF ENAMEL ENAMEL

Incremental linesIncremental lines Enamel lamellaeEnamel lamellae Enamel tuftsEnamel tufts Enamel spindleEnamel spindle Dentino-enamel junctionDentino-enamel junction

STRUCTURAL FEATURES OF ENAMELSTRUCTURAL FEATURES OF ENAMEL

CROSS STRAIATIONS (short increment) INCREMENTAL LINES

OF RETZIUS ) long increment(

Incremental lines:

INCREMENTAL LINES OF RETZIUS ) long increment(

1

3

1

3 2

1. A.D.J 2. Brown striae of Retzius3. Dentinal tubule

Brown striae of Retzius A.D.J Dentinal tubules

NEONATAL LINENEONATAL LINE

Postnatal Enamel

Prenatal Enamel

Enamel lamellaEnamel lamella

Enamel lamellaeEnamel lamellaeIn enamel

onlyExtending in enamel and

dentin

A: enamel tuft B: enamel Lamella

Enaml tufts

Enamel SpindlesEnamel Spindles

Enamel SpindlesEnamel Spindles

THE AMELODENTINAL THE AMELODENTINAL JUNCTIONJUNCTION

* 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

Enamel Rod Ends

SHALLOWERSHALLOWER CERVICALLYDEEPERDEEPER OCCLUSALLY

CRACKs

AFIBRILLAR AFIBRILLAR CEMENTUMCEMENTUM

E

C

SALIVARY PELLICLE

Life history of AmeloblastsLife history of Ameloblasts11( ( Presecretory stagePresecretory stage::

A. Morphogenic phaseA. Morphogenic phase B. Differentiation phaseB. Differentiation phase

22( ( Secretory stage (Formative stageSecretory stage (Formative stage((33( ( Maturative stageMaturative stage: :

A.Transitional phaseA.Transitional phaseB. Maturation phaseB. Maturation phase44( ( Protective stageProtective stage55( ( Desmolytic stageDesmolytic stage

11( ( Presecretory stagePresecretory stage::A. Morphogenic phaseA. Morphogenic phase

B. Differentiation phaseB. Differentiation phase

Proximal junctiponal complex

Mitochondria

Golgi apparatus

Centriol

Distal junctional complex

Basal lamina

22( ( Secretory stageSecretory stage

RER

Mitochondria

Tome‘s process

33( ( Maturative stageMaturative stageA.Transit ional phaseA.Transit ional phase

Withdrawal of Tome's Withdrawal of Tome's processesprocesses, ,

Reduction in the height Reduction in the height of the ameloblastsof the ameloblasts

and decrease in their and decrease in their volume and organelle volume and organelle

contentcontent. .

B. Maturation phaseB. Maturation phase

RUFFLED

ENDED

SMOOTH ENDED

Leaky proximal junction

Tight distal junction

Tight proximal junction

Leaky distal junction

4( Protective stageReduced dental epithelium

Amelogenesis:

Matrix formation

Maturation

primarysecondary

Tertiary

1-Stippled material secretion

Matrix formation

22--Init ial rodless (aprismatic) enamel layerInit ial rodless (aprismatic) enamel layer

STRATUM INTERMEDIUM

AMELOBLASTS

ENAMEL MATRIX

MANTLE DENTIN

Secretory ameloblast.

NO CLEAR CUT BAND OF ORGANIC MATRIX

3-Rod (prismatic) enamel layer:

44- -- -Final rodless (aprismatic) Final rodless (aprismatic) enamel layerenamel layer

The ameloblasts The ameloblasts become shorter andbecome shorter and Tomes' processes are Tomes' processes are lostlost

End of secretory ameloblast

Dentin

Rodless enamel

Rodless enamel

Rod (Prismatic) Enamel

Ameloblast without

Tomes process

ameloblast without

Tomes process

Ameloblast with

Tomes process

Beginning secretory

Secretory stage End of secretory stage

Direction of maturationDirection of maturation

Age changes of EnamelAge changes of Enamel

AttritionAttrition Decreased PermeabilityDecreased Permeability Increased Hardness (ionic exchange)Increased Hardness (ionic exchange) Color changesColor changes

Attri t ionAttri t ion

Dentin

ASG

22 - - PERMEABILITYPERMEABILITY

Main pathRecently

Erupted teeth

Old enamel

Color changesColor changes

Enamel hypoplasia