ENAMEL

بسم هللا الرحمن الرحيم

Upload By : Ahmed Ali Abbas

Babylon University College of Dentistry

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PHYSICAL CHARACTERISTICS

Hard, brittle, totally acellular , highly mineralized

Secretory product of stratified squamous epithelium

Calcified tissue

Hydroxyapatite crystal arrange in prism or rods

Density:-

Decreases from the surface of enamel to the dentino-enamel junction.

Thickness:-

Thickness over the cusps of the molars where it measures 2.5 mm & incisal edges of incisors where it is 2.0 mm.

ENAMEL

1. Forms a protective covering (2 mm – knife edge).

2. Forms a resistant covering (suitable for mastication).

3. The hardest calcified tissue in human body.

4. enamel is very brittle but the underlying dentin provides some resilience

5. Acts as semipermeable membrane (selectively permeable).

6. Color: yellowish white to grayish white depends on translucency.

Enamel gains mechanical strength by interweaving HAP crystals

Enamel rod – 5-12 million/tooth

Appatite crystal is hexagonal

Enamel initially starts with a high protein content, but these are removed and the voids backfilled with HAP as the tooth matures

CHEMICAL PROPERTIES

96% inorganic - by weight

inorganic crystalline calcium phosphate –hydroxyapatite

various ions like strontium, magnesium, lead and fluoride are present at some point during enamel formation

ENAMEL STRUCTURE

1) Enamel

rods(prisms)

2) Rod sheaths

3) Inter-rod substance.

CROSS SECTION

Cross section of enamel rod shows the key

hole pattern

Head represents the rod and key shows the

inter rod region

Head is directed towards the occlusal aspect

and tail towards the cervical region of the

tooth

CROSS SECTION OF ENAMEL

ENAMEL

CHARACTERISTICS - ENAMEL ROD/PRISM

Number: 5 – 12 millions.

Direction: Run in oblique direction and wavy

course.

Length: greater than the thickness.

Diameter average: 4 µm.

Appearance: Have a clear crystalline appearance.

Cross-section: hexagonal, round, oval, or fish

scales.

• Enamel Rod: Basic Structural Unit

Cross section

Head of enamel rod is formed by one

ameloblast and tail is formed by three

ameloblasts

Thus each rod is formed by four ameloblasts

SUBMICROSCOPIC STRUCTURE

OF ENAMEL RODS

Keyhole or paddle-shaped.

Separated by interrod substance.

About 5 µm in breadth and 9 µm in length.

The bodies are near the occlusal or incisal surface.

The tails point cervically.

The crystals; parallel to the long axis of the prism

heads.

Deviate about 65° from the tails.

ROD SHEATH

the boundary between rodand interrod is delimited bya narrow space containingorganic material – rodsheath

A thin peripheral layer.

Darker than the rod.

Relatively acid-resistant.

Less calcified and containsmore organic matter thanthe rod itself.

Electron Microscope : oftenincomplete.

ALTERNATING ROD DIRECTIONALITY

Hunter Schreger bands arealternating light and darkbands seen in a section ofenamel when cutlongitudinally and illuminatedin a special way.

•The bands are produced bythe orientation of groups ofrods.

•If the light passes throughrods cut in cross-section, theband appears light.

•If the light passes throughrods cut in longitudinally, theband appears dark.

STRIATIONS

E. rod is built-up of segments (dark lines).

Best seen in insufficient calcified E.

In a longitudinal section dark lines are seen

that shows the daily deposition of enamel

(rhythmic manner of E. matrix formation).

These lines are known as cross striation

Segment length: about 4 µm.

CROSS-STRIATIONS

Cross striations

DIRECTION OF RODS

Near the edge or cusp tip they are oblique

At the cusp tip they are almost vertical

Run from DEJ to surface of enamel

Usually at right angles to the Dentin surface.

Follow a wavy course in clockwise and anticlockwise deviation full thickness of enamel

At the cusps or incisal edges: gnarled enamel.

At pits and fissures: rods converge in their outward course.

STRAIGHT ENAMEL RODS -LONGITUDINAL

LABIOLINGUALSECTION

The enamel rods

project in the direction

of the arrow.

Can you see the striaof

Retzius?

Wavy course of enamel rod• A more spiral course is noted at cusps & incisal areas Gnarled enamel

GNARLED ENAMEL

Enamel rods are general not straight throughout their length.

In the cuspal region, the rods are very wavy.

This is referred to as gnarled enamel.

In this section, you can see the end of an odontoblasticprocesspenetrating the enamel just past the DEJ.

This structure is called an enamel spindle.

Legend

Legend: A, Gnarled enamel; B, Enamel spindle

DIRECTION OF ENAMEL RODS

HUNTERSCHRAGER BANDS

Optical phenomenon seen in reflected light

Alternate light and dark bands

Seen in ground longitudinal section

Due to abrupt change in the direction of

enamel rod

Originate from the DEJ.

HUNTER-SCHREGER BANDS

HUNTER-SCHREGER BANDS

ENAMEL -TRANSVERSE GROUND SECTION

In a transverse section of tooth, the stria of

Retzius appear as concentric bands parallel

to the dentino-enamel junction (DEJ). In

addition to the "hypo-mineralized" dark striaof

Retzius, there also exist hypo-mineralized

areas perpendicular to the DEJ. These are

enamel lamellae(that traverse the entire

thickness of enamel) and enamel

tufts(that traverse the inner third of

enamel adjacent to the DEJ

sectionLegend: A, Striaof

Retzius; B, Enamel tuft; C,

Enamel lamella; D, DEJ

STRAE OF RETZIUS

Incremental lines of growth

Eccentric growth rings

DEJ to outer surface of enamel

Where they end as shallow furrows known as

perikymata

INCREMENTAL LINES OF RETZIUS:

NEONATAL LINE

The E. of the deciduous teeth and the 1st permanent molar (It is incremental line that is the boundary between the enamel forms before and after the birth)

The neonatal line is usually the darkest and thickest striaof Retzius.

Etiology

Due to sudden change in the environment and nutrition.

The antenatal E. is better calcified than the postnatal E.

NEONATAL LINE

ENAMEL LAMELLAE

Are thin, leaf like structures,

Develop in planes of tension.

Extends from E. surface towards the DEJ.

Confused with cracks caused by grinding (decalcification).

Extend in longitudinal and radial direction.

Represent site of weakness in the tooth and three types; A, B, and C.

ENAMEL LAMELLAE

In this ground cross-section of tooth, you can see enamel lamellae and enamel tufts You can also see the neonatal line.

•What do all three of these structures have in common?

Answer: They are all hypocalcified.

Legend: A, Enamel lamella; B, Enamel tuft; C, Neonatal line

ENAMEL LAMELLAE

ENAMEL LAMELLAE

Enamel tufts are less mineralized areas of enamel in the inner third of enamel adjacent to the DEJ. They resemble tufts of grass.

•They are wavy due to the waviness of the adjacent rods.

•Structures rich in organic matter (i.e. less mineralized) that project to the surface of the enamel are enamel lamellae.

Legend: A, Enamel tufts; B, Enamel lamella

ENAMEL TUFTS -TWO PLANES OF FOCUS

Enamel tufts consist of several unconnected "leaves" of hypo-calcified enamel.

•They display a wavy twisted appearance.

•Enamel spindles are the processes of odontoblastsprojectinginto the enamel.

Legend: A, Enamel spindle; B, Enamel tuft

ENAMEL TUFTS

ENAMEL TUFTS

DENTINO-ENAMEL JUNCTION

Scalloped junction – the convexities towards

D.

At this junction, the pitted D. surface fit

rounded projections of the enamel.

The outline of the junction is performed by

the arrangement of the ameloblasts and the

B. M.

DENTINO-ENAMEL JUNCTION

ENAMEL SPINDLES

Odontoblast processesusually end at the DEJ.However, sometimes theends of the process becomeembedded in the enamel as itforms.

•These very small, usuallystraight structures that youcan see adjacent to the DEJare enamel spindles.

•They are only about onetenth the length of an enameltuft. Legend: A, Enamelspindle; B,Odontoblastprocesses indentin

Legend: A, Enamel spindle; B, Odontoblastprocess; C, Enamel rod

ODONTOBLASTIC PROCESSES AND

ENAMEL SPINDLES

THE RELATIONSHIP BETWEEN THE STRIAE OF

RETZIUZ AND SURFACE PERIKYMATA

PERIKYMATA (IMBRICATION LINES)

ARE EXTERNAL MANIFESTATIONS

OF RETZIUS STRIAE

C. ROD ENDS

Are concave and vary in depth and

shape.

Are shallow in the cervical regions.

Deep near the incisal or occlusal

edges.

ROD ENDS

D. CRACKS

Narrow fissure like structure.

Seen on almost all surfaces.

They are the outer edges of lamellae.

Extend for varying distance along the surface.

At right angles to CEJ.

Long cracks are thicker than the short one.

May reach the occlusal or incisal edge.

CRACKS

LIFE CYCLES OF THE AMELOBLASTS

According to their function, can be

divided into six stages:

1. Morphogenic stage.

2. Organizing stage.

3. Formative stage.

4. Maturative stage.

5. Protective stage.

6. Desmolytic stage.

Morphogenic stage.

React by differential growth

Produce shape of the crown

Terminal bar appears

Basal lamina separates the inner enamel epithelium and cells of the dental papilla

Pulpal layer adjacent to the basal lamina is a cell free zone

At cervical region – cell is relatively undifferentiated

Organizing stage.

Inner enamel epithelium interact with the

cells of dental papilla which differentiate into

odontoblast

Cells become elongated

Proximal part contain nuclei

Distal end is nucleus free zone

Dentin formation begins

Cell free zone disappear

As dentine is formed nutrition supply of the

inner enamel epithelium changes from dental

papilla to the capillaries that surround the

outer enamel epithelium

Reduction and gradual disappearance of the

stellate reticulum

Formative stage.

Formatve stage starts After the dentine

formation

Enamel matrix formation starts

Development of blunt cell process on the

ameloblast surface which penetrate the basal

lamina and enter the predentin

Maturative stage.

Maturation starts after most thickness of

enamel matrix formation in occlusal and

incisal area. In cervical area matrix formation

is still in progress

Ameloblast reduce in length

Cells of stratum intermedium takes spindle

shape

Protective stage.

After enamel calcification cells on ameloblast

can no longer be differentiated from stratum

intermedium and outer enamel epithelium

These layer forms reduced enamel

epithelium

Protect the enamel from connective

tissue until the tooth erupts, if it contacts

then anomalies develop enamel may be

resorbed or cementum cover may form

(afibrillar cementum)

Desmolytic stage.

Reduced enamel epithelium induces atrophy

of connective tissue separating it with oral

epithelium thus fusion of the two epithelia

can occur

Premature degeneration of the reduced

enamel epithelium may prevent the eruption

of he tooth

AMELOGENESIS

1. Organic matrix formation (follows

incremental pattern – brown striae of

Retzius).

2. Mineralization.

dpTP=distal portion of Tome’s process

ppTP=proximal portion of Tome’s process

Sg=secretory granules(E. protein)

ORGANIC MATRIX FORMATION

AMELOGENESIS

Schematic representation of

the various functional stages

in the life cycle of ameloblasts

as would occur in a human

tooth.

1, Morphogenetic stage;

2, histodifferentiation stage;

3, initial secretory stage (no

Tomes’ process);

4, secretory stage (Tomes’

process);

5, ruffle-ended ameloblast of the

maturative stage;

6, smooth-ended ameloblast of

the maturative stage;

7, protective stage.

AMELOGENESIS

RUFFLED AND SMOOTH AMELOBLASTS