Enamel

Menatalla M. Elhindawy

Enamel

Enamel Definition.Properties

A. Physical B. Chemical.

structure of enamel A. Rod. B. Inter rodC. Rod sheath.

incremental lines I. Cross striations.II. Brown striae of Retzius.III. Neonatal line.

Enamel Hypo-calssified structures.

1. Incremental lines.2. ADJ3. Enamel spindle.4. Enamel tufts.5. Enamel lamellae.

surface structure.a. Outer structureless enamel.b. perikymata.c. Rod end.d. Crackse. Afibrillar cementum .

Definition

A material like colored glass that is heated until it is liquid and then used to decorate the surface of metal, glass, or pottery.

Definition Ectodermal non-collagenous tissue covering the anatomical crown of teeth forming a protective converging against masticatory forces. It is the most highly mineralized tissue in the body.

Acellular, inert, non vital and insensitive tissue, when destroyed by any means usually wear or caries it can not be replaced or regenerated.

Enamel Definition.Properties


structure of enamel A. Rod. B. Inter rodC. Rod sheath.

incremental lines I. Cross striations.II. Brown striae of Retzius.III. Neonatal line.

Properties Physical properties 1. Color

2. Thickness

3. Hardness

4. Brittleness

5. Permeability

Properties Physical properties

1. Color

Depending on degree of translucency which depends ona. Degree of calcification.

b. Homogenisity of enamel.

Yellowish white Grayish white

More translucent More opaque

2. ThicknessVaries from 2.5 mm over the working surfaces to a

feather edge at the cervical line.


3. Hardness The hardest calcified tissue due to

a. High mineral content.b. Crystalline arrangement.

Micro-hardness is grater at surface and cusp tip than ADJ and cervical line.

Enamel of permanent teeth is harder than that of deciduous.


4. Brittleness

Brittle therefore an underlying layer of resilient dentin is necessary to maintain its integrity.


5. Permeability

It acts as a semi permeable membrane for some ions and dyestuffs of small molecular size

through pores between the crystals. Permeability is mainly from saliva to the outer

layer of enamel, but less from the pulp to the inner enamel layer across the dentin.


Properties chemical properties

By weight 96% inorganic crystalline calcium phosphate

“hydroxyapatite” Ca10 (PO4)6 (OH)2

(OH) can be replaced by F

4% organic 1-2% non-collagenous proteins “ E Prs.” and 2-3% water. Fine

lacy network, forms an envelop surrounding each

crystal.

By volume both are equal

Enamel Definition. Properties


Structure of enamel A. Rod. B. Inter rodC. Rod sheath.

Incremental lines I. Cross striations.II. Brown striae of Retzius.III. Neonatal line.

Structure of enamel

Decalcification Staining

Ground sections

Structure of enamel

Unite structure of enamel is enamel rod enveloped with rod sheath and surrounded by inter rod substance.

Enamel Rod

Rod Sheath Inter rod

substance

When rod is cut transversely, different patterns are revealed rounded, oval, fish scales & key hole.When rod is cut longitudinally it appears cylindrical separated by less calcified dark lines “cross striations”.

Structure of enamelA. Enamel Rod

I. By light microscope (L\M) Either T\S or L\S it appear clear and structure

less because of the tightly packed crystals to allow light to pass through.

The use of electron microscope with thinner sections and grater resolving power.

Structure of EnamelA. Enamel Rod

II. By electron microscope (E\M) L\S.. Cylindrical separated by less calcified dark

lines. T\S .. Oval, fish scales, rounded, hexagonal or

Key hole with the head directed occlusally and the tail points cervically.

Crystals.. at the central part parallel to the long axis of the rod. “0-40 degrees” as they approach the rod boundary, they flare laterally to an increasing degree.

The difference in the angulation causes difference in the reflective index.


III. Number Varies 5 millions at lower central and up to 12 millions at the upper 1st permanent molar.

IV. Diameter Ratio between inner and outer E. surface is 1:2.i.e. 3-4 microns at ADJ…. 8 microns at outer surface.


V. Direction


Vertical

Oblique

Vertical

Oblique

Horizontal Knife edge

VI. Course From ADJ outward … wavy course. BUT just before they reach the

outer surface they become straight. Under cusp tip or incisal edge; rods

become twisted to give maximum strength.. This is known as Gnarled Enamel.



Bands of Hunter and Schreger

An optical phenomenon produced solely by changes in rod direction.

They are seen most clearly in longitudinal ground sections viewed by reflected light.

Found in the inner two thirds of the enamel.



These bands appear as alternating dark (diazones) and light (parazones).

Scanning electron microscopy clearly reveals the difference in orientation of groups of rods within these zones.



It may be due to:1. Change in the direction of enamel

rods.2. Variation in calcification of the

enamel.3. Alternate zones having different

permeability and organic material.


Structure of enamel

Enamel Rod


substance

L\M E\M Number Diameter Direction. “P&D” Course. “G E & H-S B”

It separates enamel rods from each other.

It is as highly calcified as the enamel rods.

It has a different refractive index.

In human teeth it appears to be minimum or even absent in certain areas.

Structure of EnamelB. Inter rod Substance

Structure of EnamelB. Inter rod Substance

Structure of enamel

Enamel Rod


substance


The peripheral part of the enamel rod is called rod sheath.

It forms an incomplete envelope around the rod.

It is less calcified than the rod itself i.e. it has a higher organic content, thus it resists decalcification more than the rod.

Structure of EnamelC. Rod Sheath

It is formed along the interface between groups of crystals with different angulation in the rods and inter rod regions, due to the abrupt change in crystal orientation.

For this reason the crystals in the rod sheath are not so tightly packed, allowing more spaces between them for more organic material to be present.

Structure of EnamelC. Rod Sheath

Structure of enamel

Enamel Rod


substance


Structure of Enamel





Incremental lines Incremental means increasing or adding on, especially in a regular series.

Incremental lines of enamel means growth lines or bands seen in tooth enamel.

It includes :I. Cross striations.II. Brown striae of Ratzius.III. Neonatal line.

Incremental lines I. cross striations

Periodic bands of 3-4 µm intervals across the rod.

These represent daily rhythm of the enamel deposition.

More visible when GLS of enamel is treated with mild etching solution, the cylindrical clear crystalline enamel rod appears to be divided horizontally into equal segments by less calcified dark lines.

Also known as short increments.


Scanning E\M reveals alternating constrictions and expansions.

Close examination reveled that constrictions are concavities in the rod structure.


Brownish bands appear in the G\S of enamel.

It represents the weekly rhythm of enamel formation “periods of activity alternating with periods of rest”.

Metabolic disturbance leads to prolonged periods of rest and broadening of the incremental lines.

Incremental lines II. Brown striae of Retzius

In L/S: At the middle and cervical parts:

they run obliquely and deviate occlusally reach the enamel surface and become represented as a series of transverse depressions (perikymata).

At cusp tips and incisal ridges: these bands form semicircle as they do not reach the surface (surround the tip of dentin).


In C/S: Seen as concentric rings

resembling that of the growth rings of a tree.


The darkest stria of Retzius that occurs at the time of birth. It is due to the stress of birth.

Present only in deciduous teeth and first permanent molars (enamel develops partly before and partly after birth).

Separates prenatal enamel from postnatal enamel.

The quality of prenatal enamel is better than the postnatal enamel (more protected condition and constant nutrition of the fetus).

Incremental lines III.Neonatal Line






I. Incremental lines.II. ADJIII. Enamel spindle.IV. Enamel tufts.V. Enamel lamellae.

surface structure.a) Outer structureless enamel.b) perikymata.c) Rod end.d) Crackse) Afibrillar cementum .

Hypo-calssified structures.2. Amelo-Dentinal Junction “ADJ”The junction between enamel and dentin

is seen as a scalloped profile in ground section with the convexities directed towards the dentin.

These scallops provide undercuts that was thought at one time to be the cause of the firm attachment between enamel and dentin.

However these scallops occasionally seem to be absent and in this case the ADJ appears smooth and still enamel and dentin are firmly attached!!!!

The cause of the firm attachment is due to the interdigitating at the ADJ between the fibrils of the first formed layer of dentin and the fibrils of the organic matrix of the first formed layer of enamel.

Consequently the interdigitating between the hydroxyapatite crystals that are deposited during the mineralization of both structures.

Hypo-calssified structures.2. Amelo-Dentinal Junction “ADJ”

It is a short, straight, thin, dark structures which extend for only short distances into enamel.

They are residual tubules formed when odontoblastic processes extend across ADJ during odontogenesis before enamel forms.

Hypo-calssified structures.3. Enamel spindle.

In G\S; the odontoblastic processes disintegrate and are replaced by air which appears dark in transmitted light.

Hypo-calssified structures.3. Enamel spindle.

Ribbon like structure; project from ADJ for a short distance into enamel (1/5-1/3).

Occur developmentally because of abrupt changes in the direction of groups of rods that arise from different regions of the scalloped ADJ.

They appear to be branched and contain greater concentration of enamel proteins. They resemble tufts of grass.

Hypo-calssified structures.4. Enamel Tufts.

Best seen in transverse thick sections of enamel with low magnification.

Usually best demonstrated in G.S but can also seen in carefully demineralized sections of enamel.

Hypo-calssified structures.4. Enamel Tufts.

Fissure or leaf like defects and extend from enamel surface for varying depth in enamel.

This defect is filled with organic material.

Could help in spread of caries.Types

I. Type A “ true lamella”II. Type BIII. Type C

Hypo-calssified structures.5. Enamel Lamellae.



Type A Type CType B




surface structurea. Outer structure less enamelThe outer most 30 microns of enamel.Found in all deciduous teeth an 70% of

permanent teeth.Most common in cervical area and

least often in cusp tip or incisal edge.No rod outline is visible; crystals are

arranged parallel to each other and perpendicular to the surface.

it is highly mineralized “hyper-mineralized”

Tome’s process is absent during formation of this layer; which insure its role in rod and inter rod substance and rod sheath. “responsible for crystal arrangement”

Similar to it; there is inner structure less enamel, which is formed before Tome’s process formation.

In inner structure less enamel, crystals are arranged parallel to each other and perpendicular to dentine surface.

surface structurea. Outer structure less enamel

Outer structure less

Inner structure less ADJ

Transverse wave like groves believed to be the external manifestation of striae of Retzius.

Continuous around the tooth and parallel to the CEJ.

There are 30\mm in cervical area and decrease toward the occlusal surface to about 10\mm.

surface structureb. perikymata

They are concave depression vary in depth and shape.

They are shallow at the cervical region and deepen near the incisal or occlusal surface.

surface structurec. Rod End.

They are narrow fissure like structure found on almost all enamel surfaces and extend for varying distance.

They are actually the outer edge of enamel lamellae. Completely disappear by careful decalcification.

surface structured. Cracks.

It is coronal cementum is formed on the cervical portion of the crown; it serves no anchoring function.

Its presence is restricted to localized areas of REE degeneration.

The exposed enamel provides a surface on which cementoblasts from the dental follicle are able to deposit cementum.

surface structuree. Afibrillar cementum.

In histological sections it may appear as an "island or a "spur" of cementum continuous with radicular cementum and overlapping the cervical enamel.

Generally, coronal cementum in humans is acellular and afibrillar.

surface structuree. Afibrillar cementum.








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Enamel

Health & Medicine