Enamel

Presnted by

Dr Piyush

The anatomic crown of a tooth is covered by an

acellular, avascular, highly mineralised material

known as ENAMEL.

It is the hardest calcified tissue in the human

body.

It is the only calcified tissue arising from

ectoderm.

It contains the largest crystals among the

mineralized tissues.

It protects the less mineralised underlying

dentin of the tooth.

It serves as a surface for chewing, grinding and

crushing of food.

1) Hardness

Its high mineral content makes it the hardest substance in the human body

Surface enamel vs subsurface enamel

Hardness and density also decrease from the cuspal/incisal tip towards the cervical margin and from the surface towards the DEJ

2) Brittleness

The hardness which is comparable to mild steel makes enamel brittle.

Compensated by the cushioning effect of underlying resilient dentin.

Enamel is stiffer and more brittle than dentin.

3) Permeability

Enamel can act in a sense like a semipermeable membrane, permitting complete or partial passage of certain molecules.

4) Thickness

It varies with shape of the tooth and location

Reaching a maximum of 2.5mm in the incisal or occlusal areas and thinning down to almost a knife-edge at the CEJ

5) Color

Enamel is naturally transparent.

Ranges from yellowish white to grayish white.

Young enamel has a low translucency and whiter in colour.

The translucency increases with age and the yellow colour of underlying dentin becomes darker and more apparent with age.

6) Specific gravity- 2.8

7) Compressive strength- 384 Mpa

8) Modulus of elasticity- 84 Gpa

9) Knoop hardness number- 350-430 KHN

10) Tensile strength- 10 MPa

10) Co-efficient of thermal expansion- 11.4

11) Density- 2.97

12) Refractive index-

Average refractive index of 1.62

13) Solubility- It dissolves in acid media. It is influenced by certain ions and molecules like

fluoride, carbonates, organic matrix etc. Surface enamel is less soluble than deeper enamel14) Abrasion resistance-

Is high, allowing it to wear down slowly

Calcium hydroxyapatite[Ca10(PO4)6(OH)2].

The mineral content increases from the DEJ to the surface.

Most crystallites are regularly hexagonal in cross-section.

A fine lacy network of organic material appears between the crystal.

According to frank(1979), in the mature state, the matrix constitutes of:-

Enamel -only 0.3 %

Proteins -58%

Lipids -42%

Lactates, ions, -trace

sugars, citrates

The proteins present in enamel are:-

1.Amelogenins

2.Ameloblastin

3.Amelin

4.Enamelin

5.Tuftelin

directs the growth of the crystals

Organic matrix

acts as a cementing medium

90%.

Important in crystal growth & organization.

Nanospheres between which enamel crystals forms.

Absence leads to hypoplastic.

Also found in formation of acellular cementum.

Structure

This is structureless layer of enamel.

30µm

Present in 70% permanent teeth & all deciduous teeth.

More heavily mineralized than bulk beneath it.

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Enamel rods near

dentin at the incisal

edge or cusps forms

more complicated,

this optical

arrangement of

enamel is called

Gnarled enamel.

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Basic structural unit is the enamel prism or rod.

It consists of a tightly packed mass of millions of small, elongated hydroxyapatitecrystals in an organised pattern.

Many show fish scales

appearance in cross section.

Width is 4µm and length.

Number of rods estimated as ranging from 5 million in lower lateral incisor to 12 million in upper first molars.

Diameter of enamel increases from DEJ to outer surface at a ratio about 1:2.

The cross-sectional--the keyhole arrangement of enamel prisms with the heads pointing occlusally and the tails pointing cervically.

Head of each rod is made up of 1 ameloblast and tail is made up of 3 ameloblasts.

Human enamel

contains rods

surrounded by rod

sheath and separated

by interrod substance.

Most common pattern

of enamel is keyhole

or paddle shaped

prism.

In a longitudinal section, appearance of

rods separate by interrod substance.

Polarized light and roentgen-ray study

indicated that apatite crystals are

arranged approximately parallel to long

axis of prisms.

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It confers strength to the enamel.

Their direction is an important consideration in

the cavity preparation for restorations

Enamel rods that are supported by hard

restorative material rather than more pliant

dentin are more likely to fracture

Fracturing of unsupported rods in poorly designed restorative preparations causes loss of enamel around the margins of the filling material resulting in marginal leakage and makes the tooth more susceptible to carious attack.

Additionally, it is also important to note that the inclination of rods differs in permanent and primary teeth and must be accounted for during cavity preparation.

Each enamel rod is built up of segments

separated by dark lines that give it a

striated appearance.

The striations are more pronounced in

enamel that is insufficiently calcified.

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Generally they are oriented at right angle to dentin.

Near the incisal edge or cusp tip they change gradually to an increasingly oblique direction until they are almost vertical in the region of edge or tip of cusp.

In cervical and central parts of deciduous tooth

they are approximately horizontal.

More or less changes in the direction of rods may be regarded as functional adaptation minimizing the risk of cleavage due to occlusalloading forces. This changes in direction of rods is responsible for appearance the Hunter-Schreger bands.

Careful decalcification and staining gives evidence that these are not solely optical phenomenon.

These are composed of zones different permeability and organic content.

Some books suggest that this is an optical phenomenon produced merely by changes in direction of lights.

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They appears as brownish bands in ground section of the enamel.

They illustrate the incrimentalpattern of enamel, during formation of crown.

They reflect variation in structure and mineralisation, and are either hypomineralisedor hypermineralised.

Banding patterns formed during illness will

show up on contralateral teeth which are

developing at the same time.

Patterns of enamel hypoplasia on a single tooth

or on one side indicate trauma or a localised

rather than systemic infection.

A delicate membrane that covers entire portion

of newly erupted crown is enamel cuticle or

Nasmyth’s membrane.

It soon get removed by mastication.

This is secreted by ameloblast when enamel

formation is complete.

This is hypomineralised structure.

Thin, leaflikestructures.

Penetrate into dentin.

Organic material.

This is hypomineralisedstructure.

Lamellae may develop in planes of tension.

Where rods cross such a plane, a short segment

of the rod may not fully calcify.

This leads to formation of three types of

lamellae:-

type A:- poorly calcified rods

type B:- degenerated cells

type C:- arising in erupted teeth where the cracks are

filled organic matter, presumably originating from saliva.

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Represents a significant weakness in the

structure of enamel and is susceptible to

cracking and and form a road for the entry of

bacteria that initiate caries.

Arise at the DEJ and

reach into enamel to

about one fifth to one

third of its thickness.

Tufts consists of

hypocalcified enamel

rods and interprismatic

substances.

Tufts are hypomineralised

structure.

No major clinical significance, but represent

areas of enamel weakness.

The surface of dentin at DEJ is pitted which fit rounded projections of enamel.

Scalloped appearance.

The DEJ is more prominent in the occlusal area.

It is hypomineralisedstructure.

Occasionally odontoblast

processes pass across the

DEJ into enamel, many

of them are thickened at

there end, they are

termed as enamel

spindles.

This is hypomineralised

structure.

No major clinical significance but may confer

additional permeability to the deeper layers of

enamel.

Striae of Retzius often

extends from DEJ to

outer surface, when

they end in shallow

furrows known as

Perikymata

1) Prismless enamel- Primary teeth are more

likely to have a prismless surface zone than

are permanent teeth. A difference in the

reaction to conditioning agents is suspected

because less etching occurs on primary tooth

than on permanent tooth enamel during acid

conditioning.

2) Thickness- enamel is twice as thick on

permanent teeth as in primary teeth.

3) Neonatal line-it is the

most prominent

incremental line in

primary teeth.it is due

to the metabolic trauma

to the developing tooth

at or near the time of

birth. Prenatal enamel

is less pigmented and

more free of defects

than postnatal enamel.

4)Enamel of primary teeth is whiter than that of

permanent teeth. This is believed to be because

much of primary tooth enamel is formed

prenatally and is not subject to some

enviornmental factors.

5)Direction of enamel rods-in the cervical area

the enamel rods in primary teeth are oriented

horizontally while in permanent teeth they are

inclined apically.

As the development of tooth progresses through

various stages of tooth development, the actual

formation of starts once ameloblasts are formed.

Ameloblasts are formed when tooth

development progresses to formation of bell

stage.

Enamel organ

Dental lamina

Dental papilla

Outer Enamel Epithelium

Stellate Reticulum

Stratum Intermedium

Inner Enamel Epithelium

It consists of a single layer of cuboidal cells.

Function-

Exchange of substances between the enamel organ and the environment.

It forms the middle part of the enamel organ

The cells are star shaped

Function-Permit only a limited

flow of nutritional elements from the outlying blood vessels to the formative cells.

The cells of the stratum intermediumare situated between the stellate reticulum and the inner enamel epithelium.

They are flat to cuboid in shape

Function-Play role in

enamel formation

Before enamel formation begins these cells assume a columnar form and differentiate into ameloblasts that produce the enamel matrix.

The borderline between the inner enamel epithelium and the connective tissue of the dental papilla is the subsequent DEJ

Development of enamel is described in two

parts:-

A. Life cycle of ameloblasts

B. Amelogenesis

Morphogenic stage

Organizing stage

Formative stage

Maturative stage

Protective stage

Desmolytic stage

Before ameloblast differentiate and produce

enamel, they interact with adjacent

mesenchymal cells, determining shape of DEJ &

crown.

During this stage cells are short columnar with

oval nuclei that almost fill cell body.

• This is characterized by presence of cells in inner el

epithelium.

During this stage there is changes in

organization and number of cytoplasmic

organelles related to initiation of enamel matrix.

• Enamel maturation begins after most of thickness of

enamel matrix has been laid down.

Ameloblast after maturation of enamel matrix

forms a protective layer i.e. reduced enamel

epithelium which is protective to enamel until

tooth erupt in oral cavity.

By desmolysis the cells of reduced enamel

epithelium help in eruption of tooth.

There are two processes involved in

development of enamel

Formation of enamel matrix

Maturation

Secretory activity starts when a small amount of

dentin is laid down.

Ameloblasts lose their projections.

Islands of enamel matrix are deposited.

A thin continuous layer of enamel is formed

along the dentin called dentinoenamel

membrane.

The surface of ameloblasts facing developing enamel are not smooth

There are interdigitation of cells and enamel rods that they produce. These projections into enamel matrix have been named Tomes’ processes

The head of each rod is formed by one

ameloblast where as 3 others contribute to

tail of each rod. That is each rod is formed

by four ameloblasts and each ameloblast

contributes to four different rods.

Ameloblasts are shorter.

They have a villous surface near the enamel and ends of cells are packed with mitochondria-typical of absorptive cells.

Organic components and water are lost during mineralization.

Over 90% of initially secreted protein is lost.

It takes place in two stages:-

First, an immediate partial mineralisation -25-30% of the total mineral content

The second stage, or maturation is characterised by gradual completion of mineralisation

Each rod matures from the depth to the surface, and sequence of maturing rods is from cusps or incisal edge toward the cervical

DESTRUCTION OF ENAMEL-

Bacterial

i.e. Dental caries

Non Bacterial

i.e.

attrition,abrasion,erosion,abfraction

Dental CariesThe high mineral content of enamel which

makes this tissue the hardest in the human

body , also makes it susceptible to a

demineralisation process which often occurs as

dental caries.

Enamel caries is of two types:-

1)Smooth surface caries

2)Pit and fissure caries

The initial lesion is a white spot

Eventual loss of continuity of the enamel surface which feels rough to the point of an explorer

It typically forms a triangular or a cone shaped lesion with the apex towards the DEJ and the base towards the surface

The carious process has extended into dentin but there is still no cavitation

Before complete disintegration of enamel

several zones can be distinguished,

beginning on the dentinal side of the

lesion:-

ZONE 1-the translucent zone

ZONE 2-the dark zone

ZONE 3-the body of the lesion

ZONE 4-the surface zone

Caries beginning in a fissure with decalcification extending from its sides and bottom.

It forms a cone shaped lesion with the base at the DEJ and apex at towards the surface

It reaches the dentin and spreads laterally.

There is separation of enamel and dentin and fracture of the enamel roof.

Attrition

Abrasion

Erosion

Abfraction

The physiologic

wearing away of a

tooth as a result of

tooth-tooth contact.

This phenomenon is

physiologic rather

than pathologic

Pathologic wearing

away of tooth

substance through

some abnormal

mechanical process.

Generally occurs on

exposed surfaces of

roots.

Irreversible loss of

dental hard tissue by

a chemical process

that does not involve

bacteria.

Erosion is also related

to GERD.

Pathologic loss of

both enamel and

dentin caused by

biomechanical loading

forces.

Amelogenesis Imperfecta

Enamel Hypoplasia

Mottled Enamel

Enamel Pearls

Tetracycline Stains

A structural defect of

tooth enamel.

There is disturbance in

the differentiation or

viability of ameloblast.

Both deciduous as well

as permanent dentitions

usually are involved.

Three main groups: hypoplastic(60-73%),

hypocalcified(7%), and hypomature(20-40%).

Classification of amelogenesis imperfecta

according to Witcop :-

Type Ι Hypoplastic

Type ΙΙ Hypomaturation

Type ΙΙΙ Hypocalcified

Type ΙV Hypomaturation-hypoplastic with

taurodontism

No specific treatment, except for

improvement of cosmetic appearance.

Incomplete or defective formation of organic

enamel matrix.

Rickets during formation of enamel is most

common cause of Enamel hypoplasia.

As rickets is not a prevelant disease, vitamin A

& C have been named as cause.

Considerable contraversy are there about any

relation between caries & enamel hypoplasia. It

is most reasonable to assume that the two are

not related, although hypoplastic teeth appear

to decay at somewhat more rapid rate once

caries has been initiated.

Term mottled enamel is described by GV Black

and Frederick S McKay in 1916.

Ingestion of fluoride containing water during

time tooth formation is most important.

More than 1 ppm of fluoride causes significant

mottling.

0

There is wide range of

severity in the

appearance of mottled

teeth, varying from

I. Mild changes (white

opaque areas)

II. Moderate and severe

(pitting and brownish

staining)

III. A corroded appearance of

the teeth.

Discoloration occurs due to prophylactic administration of tetracycline to pregnant female or postpartum in the infants.

Yellowish or brownish-gray discoloration.

Crucial period is 4 months in utero to about 7 years of age.

The direction of enamel rods is of

importance in cavity preparation:

One of the most important principles in tooth

preparation is the concept of the strongest

enamel margin

It is formed by full length enamel rods whose

inner ends are on sound dentin.

The American Society for Testing and Materials

defines adhesion as “the state in which two

surfaces are held together by interfacial forces

which may consist of valence forces or

interlocking forces of both”.

Advantages

1) Cusp reinforcement after tooth preparation.

2) Reinforce remaining enamel and dentin.

It is important technique in

clinical practice.

It involves use of etchant to

produce change in surface

texture of enamel.

There are three types of Enamel etching seen

Type A- Dissolve enamel rod

Type B- Dissolve interrod enamel

Type C- Irregular and indiscriminate

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It achieves desired effects in two stages:-

1) Removes plaque and other debris

2) Increases the porosity of exposed surfaces

Increases the free surface energy of enamel.

Micromechanical bonding.

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Bleaching may be defined as the lightening of color of tooth through application of chemical agent to oxidize organic pigmentation of tooth.

H₂O₂ has low molecular weight that enables it to fuse through enamel.

Oxidation reaction

Low pH can cause destruction of enamel by

demineralisation

i) Microabrasion-

Microabrasion techniques improve appearance

of fluorotic teeth.

McCloskey reported that Kane succesfully removed

fluorosis stains by applying acid and heat in 1916.

In 1960s, McInnes used five parts of 36% HCL, five

parts of 30% H₂O₂ and one part of Ether.

Ether – Removes surface debris

HCL – Etches Enamel

H₂O₂- Bleaches Enamel

Fluoride-stained teeth are difficult to bleach

and require longer and repeated sessions to

decolorize them.

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ii) Macroabrasion –

an alternative method to removal of superficial white spots.

Uses a 12-fluted composite finishing bur or a fine grit finishing diamond at high speed.

Next, a 30-fluted composite finishing bur is used.

Final polishing is achieved with an abrasive rubber point.

Increases resistance to caries.

Melting and fusing of enamel-70-85%resistant to

acids.

When laser technique is used with fluoride -

cavities were completely stopped.

absorption of fluoride ions on enamel

This increases resistance to acid dissolution

of enamel

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Orban’s oral histology and embryology .

Oral histology- Tencate .

Dental embryology, histology and anatomy-Mary Bath-Balogh And Margaret J. Fehrenbach.

Textbook of operative dentistry- Sturdevant.

Grossman’s Endodontic Practice.

Philips’- Science of Dental Material.