Dental Anatomy: Enamel

ENAMEL
Dr. Mohsen S. Mohamed
BDS, Misr International Universtiy, Cairo, Egypt.
Certification, Universitätsklinikum Carl Gustav Carus.
Owner and Author of OziDent.com
Dental Anatomy
Created For www.Ozident.com

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.

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.

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

•E. rod is built-up of segments (dark lines).
•Best seen in insufficient calcified E.
•Represent rhythmic manner of E. matrix
formation.
•Segment length: about 4 µm.
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

•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
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.

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.

SURFACE
STRUCTURES

Surface Structures
a. Structureless layer (E. skin)
b. Perikymata
c. Rod ends
d. Cracks
e. Enamel cuticle

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.

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.

e. Enamel cuticle
1. Primary E. cuticle (Nasmyth’s
membrane).
2. Secondary E. cutile (afibrilar
cementum).
3. Pellicle (a precipitate of salivary
proteins.

Primary enamel cuticle
 Covers the entire crown of newly erupted
tooth.
 Thickness: 0.2 µm.
 Removed by mastication (remains intact in
protective areas).
 Secreted by postamloblasts.
 EM: similar to basal lamina.

Secondary enamel cuticle
 Covered the cervical area of the enamel.
 Thickness: up to 10 µm.
 Continuous with the cementum.
 Probably of mesodermal origin or may be
elaborated by the attachment epithelium.
 Secreted after E.O. retracted from the cervical
region during tooth development.

Pellicle
 Re-form within hours after mechanical
cleaning .
 May be colonized by microorganisms to form a
bacterial plaque.
 Plaque may be calcified forming calculus.

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
Type A Type B Type C
Consistency Poorly calcified rod
seg.
Degenerated cells Organic matter
from saliva
Tooth Unerupted Unerupted Erupted
Location Restricted to the E. Reach into the D. Reach into the D.
Occurrence Less common Less common More common

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).

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.

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

LIFE CYCLES OF THE
AMELOBLASTS

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.

Amelogenesis
1. Organic matrix formation (follows
incremental pattern – brown striae of
Retzius).
2. Mineralization.

Organic Matrix Formation
a. Amelodentinal membrane.
b. Development of Tome’s processes.
c. Distal terminal bars.
d. Ameloblasts covering maturing enamel.

dpTP=distal portion of Tome’s process
ppTP=proximal portion of Tome’s process
Sg=secretory granules(E. protein)
Organic Matrix Formation

Ameloblasts are perpendicular to the rods
(arrow=cell membrane, p=Tome’s process, s=incomplete septum)

Depression in enamel surface which were
occupied by Tome’s processes

Mineralization
a. Partial mineralization (25-30%).
b. Maturation (gradual completion of
mineralization).

Crystal Mineralization
Recently formed crystals Mature crystals

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

Dental Anatomy: Enamel

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