This Slide, gives a Brief introduction to the Anatomy of the tooth specifically the outer shell, the enamel, including the structures, development and abnormalities.
Created by Dr. Mohsen S. Mohamed
For Ozident.com
1. 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
2. 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.
4. 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.
5. 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.
7. 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.
9. 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.
14. 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
15. •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
16. •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
18. •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
20. •Alternating dark and light strips.
•Have varying width.
•Seen in large ground section (oblique
reflected light).
•Originate from the DEJ.
Hunter-Schreger Bands
23. 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.
25. 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.
27. 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.
31. 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.
32. 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)
33. The relationship between the striae
of Retziuz and surface perikymata
Striae of Retziuz Perikymata
34. c. Rod ends
Are concave and vary in depth and shape.
Are shallow in the cervical regions.
Deep near the incisal or occlusal edges.
36. 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.
38. e. Enamel cuticle
1. Primary E. cuticle (Nasmyth’s
membrane).
2. Secondary E. cutile (afibrilar
cementum).
3. Pellicle (a precipitate of salivary
proteins.
39. 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.
40. 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.
41. Pellicle
Re-form within hours after mechanical
cleaning .
May be colonized by microorganisms to form a
bacterial plaque.
Plaque may be calcified forming calculus.
43. 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.
44. 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
48. 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).
52. 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.
55. 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.
57. LIFE CYCLES OF THE
AMELOBLASTS
Created For www.Ozident.com
58. 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.
60. Organic Matrix Formation
a. Amelodentinal membrane.
b. Development of Tome’s processes.
c. Distal terminal bars.
d. Ameloblasts covering maturing enamel.
61. dpTP=distal portion of Tome’s process
ppTP=proximal portion of Tome’s process
Sg=secretory granules(E. protein)
Organic Matrix Formation
66. 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.