3-enamel Mona

:Histological Study of Hard Dental Tissues Physical properties Chemical Composition Inorganic phase Organic phase

Development (genesis): Forming cells: (life history) Matrix formation (protein synthesis) Calcification (mineralization)

Ultra-structure Structural unit-Regional variation

Incremental lines Age changes 

ENAMEL The hardest calcified tissue in the body forms the protective covering of the crown

:PHYSICAL PROPERTIES COLO R TH ICKNES S HAR DNESS BRI TT LEN ESS PER MEA BILI TY

*

COLOUR - 1 YELLOWIH WHITE TO GRAYISH WHITE

: Depends on Degree of -1 calcification Homogenisity of -2 the enamel YELLOWISH teeth…. Translucent enamel

THICKNESS - 2 mm 2.5 – 2. at the cusps of the molars and .premolars Thinning down to almost knife edge at the cervical margin of the tooth

HARDNESS – 3 ENAMELIT IS THE HARDEST MICROHARDNESS ENAMEL OF - AT IN CALCIFIED TISSUE IS - 1GREATEST THETHE PERMANENT THE BODY SURFACE AND TEETH :DUE TO E. IS DECREASED TOWARD HARDER THANOF -1 HIGH CONTENT .DEJ THAT OF SALTS ITTHE IS - MINERAL 2 GREATER AT THE DECIDUOUS ITS CRYSTALLINE CUSPS AND INCISAL-2 ’ONES .ARRANGEMENT RIDGE ANDDECREASES TOWARD THECERVICAL .LINE

+

+

+ -

+ -

-

BRITTLNESS - 4 ITS STRUCTURE AND HARDNESS RENDER IT BRITTLE, SPECILY WHEN IT LOOSES ITS ELASTIC FOUNDATION OF HEALTHY DENTIN

ASG

PERMEABILITY -5

CERTAIN ENAMEL HAS ADEGREE OF MAINLY PER. ISPERMEABILTY DEMONSTRATED FROM SALIVA TOBY DYES AND RADIOACTIVE OUTER LAYER OF ISOTOPES ENAMEL, BUT LESS T FROM ACTS THE AS A PULP TO SEMIPERMEABLE THE INNER ENAMEL MEMBRANE FOR LAYER ACROSS CERTAIN IONS AND .THE DENTIN DYESTUFFS OF SMALL MOLECULAR SIZE THROUGH PORES BETWEEN THE

:CHEMICAL COMPOSITION INORGANIC CONTENT

By weight

96% CRYSTALLINE CALCIUM PHOSPHATE

“HYDROXYAPATITE” Ca 10(PO4)6 (OH)2

ORGANIC CONTENT 4%

AMELOGENINS ENAMELINS and Water

GROUND SECTION

DECALCIFIED SECTION

Methods of Studying ”hard tissues ”

:STRUCTURAL UNIT

ENAMEL ROD or PRISM

NUMBER: DIRECTION: COURSE:

DIAMETER:

:Longitudinal section : Cross Section

ENAMEL PRISM LOWER CENTRAL INCISOR

NUMBER - 1

5

MILLIONS

UPPER FIRST MOLAR

12

MILLIONS

DIRECTION - 2 D

D

p

ENAMEL PRISM 3 - COURSE

DENTINO-ENAMEL MEMBRANE

STRUCTURELESS ENAMEL

Wavy Course of Enamel Rods

GNARLED ENAMEL

: longitudinal Section

: Cross Section ,Hexagonal, fish scales keyhole pattern

Ameloblast

Tomes process

SUBMICROSCOPIC STRUCTURE OF ENAMEL ROD Key hole analogy Enamel rod

T.S

T.S

L.S

L.S

Enamel prism Head of keyhole “core”

Key-hole Interprismatic Prism Pattern region “Tail region”

sheath

Boundary around” the head

HUNTER-SCHREGER BANDS

(optical phenomenon) dark and light bands

HISTOLOGICAL STRUCTURES OF ENAMEL     

Incremental lines Enamel lamellae Enamel tufts Enamel spindle Dentinoenamel junction

STRUCTURAL FEATURES OF ENAMEL

Incremental lines:  CROSS STRAIATIONS (short increment)  INCREMENTAL LINES OF RETZIUS (long increment )

 INCREMENTAL LINES OF RETZIUS (long increment )

Cross Striations

Enamel Rods

Incremental lines of Retzius

• NEONATAL LINE

dentin

d PRENATAL ENAMEL

POSTNATAL ENAMEL

Before birth

After birth

POSTNATAL ENAMEL

PRENATAL ENAMEL

Incremental lines of Retzius Surface manifestation : Perikymata

Structural features in Enamel  1- ENAMEL LAMELLAE

 2-

ENAMEL TUFTS

 3- Dentino - Enamel Junction

Enamel lamellae

Enamel lamellae In enamel only

Extending in enamel and dentin

Enamel Spindles

THE AMELODENTINAL JUNCTION ENAMEL

DENTIN

PRIMARY ENAMEL CUTICLE ((Nasmyth’s membrane - 0.2 um thick. - Its structure is similar to the basal lamina of the epithelium. - It is the last product of the ameloblasts. ASG

PR IM ARY ENA ME L C UT IC LE

1ry e.cuticle

Longitudinal Ground Section

Transverse Ground Section

HUNTER-SCHREGER BANDS

(optical phenomenon) dark and light bands

Observed in L.s ground section under reflected light

 SURFACE STRUCTURES OF ENAMEL

* OUTER STRUCTURELESS ENAMEL *PERIK YMAT A

*E NAME L RO D E NDS * CRACK s *Afibrillar

cem ent um

SURFACE STRUCTURES OUTER STRUCTURELESS ENAMEL – 1 REMEMBER: THAT THERE IS AN INNER STRUCTURELESS ENAMEL

um thick 30

Perikymata Surface manifestation of Incremental lines of Retzius

Perikymata

PARALLELTO EACH OTHER AND TO C.E.J. CONTINUOUSAROUND THE TOOTH. 30/ mm – AT THE REGION OF C.E.J. 10/ mm – NEAR TO THE OCCLUSAL OR INCISAL EDGES

Enamel Rod Ends

SHALLOWER CERVICALLY DEEPER OCCLUSALLY

CRACKs

AFIBRILLAR CEMENTUM E

C

SALIVARY PELLICLE

Age changes of Enamel   



Attrition Decreased Permeability Increased Hardness (ionic exchange) Color changes

Attrition Dentin

PERMEABILITY - 2

Recently Erupted teeth ASG

Main path

Old enamel