2 enamel 2010
DESCRIPTION
Enamel & Amelogenesis :)TRANSCRIPT
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