ENAMEL

Dr. Muznah Sultan

Lecturer DIDC-DUHS

Dental Anatomy

Physical Characteristics

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. Brittle.

5. The specific gravity is 2.8.

6. Acts as semipermeable membrane.

7. Color: yellowish white to grayish white.

Tooth Layers

longitudinal cross section of the Tooth showing :

Enamel, Dentine, Pulp and Cementum

Chemical Properties

• Inorganic materials (apatite crystals) 96%

By weight

• Organic substances and water 4%

• In volume the organic matter and water

are nearly equal to the inorganic

contents.

Structure

I. Prisms or rods.

II. Rod sheath.

III. Inter-prismatic substance.

IV. Striations.

V. Direction of rods.

VI. Hunter-Schreger bands.

VII. Incremental lines.

VIII. Surface structures.

IX. Enamel lamellae.

X. Enamel tufts.

XI. Dentino-enamel junction.

XII. Odontoblastic processes and enamel spindles.

Enamel Rods or Prisms

Characteristics

Number: 5 – 12 millions.

Direction: Run in oblique direction and wavy

course.

Length: greater than the thickness of E.

Diameter average: 4 µm.

Appearance: Have a clear crystalline

appearance.

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

scales.

Enamel Rods

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.

Keyhole shaped E. rods

Hexagonal ameloblasts

Note crystal orientation

Enamel Rod’s Shape

Crystals in rod and inter-rod enamel are similar in structure but diverge in

orientation

Enamel Crystal

Crystals length: 0.05 – 1 µm.

Thickness: about 300 A°.

Average width: about 900 A°.

Cross sections: somewhat irregular.

Enamel Crystal

Longitudinal Section Transverse Section

A thin peripheral layer.

Darker than the rod.

Relatively acid-resistant.

Less calcified and contains more organic matter than the rod itself.

Electron Microscope : often incomplete.

The Rod Sheath

•Cementing E. rods together.

•More calcified than the rod sheath.

•Less calcified than the rod itself.

•Appears to be minimum in human teeth.

Inter-prismatic Substance

Cross-striations

•Usually at right angles to the D. surface.

•Follow a wavy course in clockwise and

anticlockwise deviation.

•At the cusps or incisal edges: gnarled

enamel.

•At pits and fissures: rods converge in their

outward course.

Direction of Rods

Direction of Enamel Rods

•Alternating dark and light strips.

•Have varying width.

•Seen in large ground section (oblique

reflected light).

•Originate from the DEJ.

Hunter-Schreger Bands

Hunter-Schreger Bands

Hunter-Schreger Bands

Hunter-Schreger Bands

This is Due to:

1. Change in the direction of E. rods.

2. Variation in calcification of the E.

3. Alternate zones having different permeability and organic material.

4. Optical phenomenon.

A. Incremental Lines of Retzius

B. Neonatal Line

Incremental Lines

Incremental Lines of Retzius:

Brownish bands in ground sections.

Reflect variation in structure and mineralization.

Broadening of these lines occur in metabolic disturbances.

Etiology

1. Periodic bending of E. rods.

2. Variation in organic structure.

3. Physiologic calcification rhythm.

Incremental Lines of Retzius:

Neonatal Line

The E. of the deciduous teeth and the 1st

permanent molar develop partly before birth

and partly after birth, the boundary between

both is marked by neonatal line or ring.

Etioloyg

Due to sudden change in the environment and

nutrition.

The antenatal E. is better calcified than the

postnatal E.

Neonatal Line

SURFACE

STRUCTURES

Surface Structures

a. Structureless layer (E. skin)

b. Perikymata

c. Rod ends

d. Cracks

a. Structureless layer

About 30 µm thick.

In 70% permanent teeth and all deciduous teeth.

Found least often over the cusp tips.

Found commonly in the cervical areas.

No E. prisms.

All the apatite crystals area parallel to one another and

perpendicular to the striae of Retzius.

More mineralized than the bulk of E. beneath it.

b. Perikymata

Transverse wave like grooves.

Thought to be the external manifestation of the striae of Retzius.

Lie parallel to each other and to CEJ.

Number:

About 30 perik./mm at the CEJ.

About 10 perik./mm near the incisal edge.

Their course is regular, but in the cervical region, it may be quite irregular.

Powdered graphite demonstrates them.

It is absent in the occlusal part of deciduous teeth but present in postnatal cervical part (due to undisturbed and even development of E. before birth)

The relationship between the striae

of Retziuz and surface perikymata

Striae of Retziuz Perikymata

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

ENAMEL LAMELLAE

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

Enamel Lamellae

ENAMEL TUFTS

Enamel Tufts

Arise from DEJ.

Reach to 1/5 – 1/3 the thickness of E.

In ground section: resemble tufts of grass.

Do not spring from a single small area.

The inner end arises at the dentin.

Consist of hypocalcified E. rods and interprismatic substance.

The extend in the direction of the long axis of the crown (best seen in horizontal sections).

Enamel Tufts

Enamel Tufts

DENTINO-ENAMEL

JUNCTION

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

ODONTOBLASTIC

PROCESSES AND

ENAMEL SPINDLES

Odontoblastic Processes and

Enamel Spindles

The odontoblasts processes may cross DEJ (before the hard substance is formed) to the E. and ends as E. spindles.

They are filled with organic matter.

The processes and spindles are at right angle to the surface of the dentin.

The direction of spindles and rods is divergent.

Spindles appear dark in ground sections under transmitted light.

Odontoblastic Processes and

Enamel Spindles

Abnormalities

Interference during E. matrix formation may

cause Enamel hypoplasia.

Interference during Enamel maturation may

cause Enamel hypocalcification.

Each condition may be caused by systemic,

local, or hereditary factors.

Abnormalities

Enamel Hypocalcification Enamel Hypoplasia

Thank you!!