dental anatomy: enamel
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ENAMELDr. Mohsen S. MohamedBDS, Misr International Universtiy, Cairo, Egypt.Certification, Universitätsklinikum Carl Gustav Carus.Owner and Author of OziDent.com
Dental Anatomy
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Physical Characteristics1. 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
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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.
StructureI. 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. rodsHexagonal ameloblasts
Note crystal orientation
Enamel Rod’s Shape
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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
Cross-striations
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•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 BandsThis 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 RetziusB. 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
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Surface Structuresa. Structureless layer (E. skin)
b. Perikymata
c. Rod ends
d. Cracks
e. Enamel cuticle
a. Structureless layerAbout 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
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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
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e. Enamel cuticle1. 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 Created For www.Ozident.com
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 LamellaeType 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 Lamellae
Enamel Lamellae
ENAMEL TUFTS Created For www.Ozident.com
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
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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
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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
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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.
1
2
3
4 5
6
Amelogenesis1. Organic matrix formation (follows
incremental pattern – brown striae of Retzius).
2. Mineralization.
Organic Matrix Formationa. 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
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(arrow=cell membrane, p=Tome’s process, s=incomplete septum)
Depression in enamel surface which were occupied by Tome’s processes
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Mineralizationa. 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
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