ENAMEL

Physical characteristics

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• Hardest calcified tissue - resistant covering of teeth
• Yellowish white –grayish white
• Thickness – max 2-2.5mm
• Specific gravity -2.8
• Semipermeable
• Temp resistance : 5-13 Hz
• Transmission coeifficient at 525 nm- 0.481 mm

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CHEMICAL PROPERTIES

• Inorganic - 96% Organic + water- 4%

Hydroxy apatite

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• Organic

Amelogenins & Non amelogenins

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A.Amelogenins (90%)

Low mol wt rich in proline,histidine,glutamine and leucine

B.Non Amelogenins (10%)

High mol wt rich in glycine,aspartic acid and serine

Eg; Enamelin, Ameloblastin, Tuftlin

• Inorganic material – Hydroxy apatite
• Ca10 (po4)6 (OH4)
• Na,Mg,C,O2,Ca,P
• Crystals hexagonal in CS
• Crystals arranged to form enamel rods/prisms
• Hydroxyapatite

- central core of OH iron

- surrounding calcium & phosphorous ---- triangles

- Mg ---- ca carbonate ---- OH (from surface – DEJ)

O2 – 43.4%, Ca – 36.6%,P – 17.7% Minor – 2.3% (Na 0.67,ca -0.64,Mg-0.35)

• A) Water - b/w crystals, B) b/w rods & surrounding rods

C) in pores b/w crystals

STRUCTURE

• Enamel rods/prisms + rod sheath + interprismatic substance
• Enamel prisms are cylindrical in LS ,
• Cross section - light microscopy: hexagonal/oval
• Ranges from 5-12 million
• Length > thickness : Oblique &wavy course of rods
• Increase in area of enamel at the surface
• Increase in diameter of rods towards the surface (1:2)

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• Enamel rod – clear crystalline appearance
• Cross section - light microscopy: hexagonal/oval
• Human enamel (CS): resemble Fish scale
• Ultrastructure : Key hole /paddle shape

• Rod – 5µm breadth 9µm length
• “Bodies” of rods – near occlusal/incisal
• “Tails”- point cervically

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• Orientation of apatite crystals

II to long axis in body/head

65 degree deviation in tails

Striations�

• Enamel rod is built of segments seperated by dark lines that gives a striated appearance
• cross striations demarcate rod segments
• Rods segmented –
• enamel forms rythamically
• Segments - 4 µm length

Direction of rods

• Generally right angles to dentin surface
• Deciduous teeth :

Central & cervical – horizontal

Incisal edge & cusp tips – oblique to vertical

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• Permanent teeth:

Cervical reg - deviate from horizontal in an

apical direction

Hunterschreger bands

• More or less regular change in the direction of rods may be regarded as functional adaptation minimizing the risk of cleavage in the axial direction under the influence of occlusal masticatory forces.

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• The change in direction is responsible

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• Alternating dark and light strips of varrying widths

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• Best viewed in LS under oblique reflected light

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diazones

parazones

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• from DEJ pass outward ending short of enamel surface.
• The prisms that are cut in longitudinally produce the dark bands called Diazones and while that are cut transversely to produce light bands are called Parazones.
• The angle between parazones and diazones is 40 degrees.
• Alternate zones having difference in permiabilty and organic content

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GNARLED ENAMEL

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• Middle of the crown ----- horizontal disks
• Rods in adjacent disks bend in opposite direction (right & left)
• Alternating clockwise &counter-clockwise deviation from radial direction – at all levels
• Disk cut in oblique near dentin- region of cusps or incisal edges ---- the rod arrangement appears further complicated
• Bundles of rods seem to intertwine more irregularly
• This optical phenomenon called gnarled enamel

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INCREMENTAL LINES OF RETZIUS

• Brownish bands in ground sections
• successive apposition of layers of enamel during formation of crown
• LS - surrounding the tip of the dentin

cervical - run obliquely

from DEJ to surface - deviate occlusally

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• TS - appear as concentric circles

• Reflect variation in structure&mineralization (hypo/hyper)

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• Periodic bending of rods to variations in basic structure

or to a physiologic calcification rhythm.

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• Daily rate of enamel formation - 3.5µm

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NEONATAL LINE

• Enamel of deciduous teeth develops partly before birth and parltly after birth. + permanent molars
• Boundary b/w two portions of enamel marked by an accentuated incremental line of Retzius Neonatal line /Neonatal ring
• As a result of abrupt change in environment & nutrition

SURFACE STRUCTURES

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• Prismless enamel /Aprismatic enamel
• Perikymata
• Rod ends
• Cracks
• Enamel cuticle
• Enamel lamellae
• Pellicle
• Neonatal Line
• Afibrillar cementum

Prismless enamel :

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• Cusp tip & cervical
• Structureless Layer, 30 µm
• 70% of permanent & all deciduous
• Prism outlines not visible,
• apatite crystals II to one another
• Heavily mineralized

PERIKYMATA :

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• Transverse wave –like grooves believed to be external manifestation of striae of Retzius

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• Continuous around the tooth
• Paralell to each other and to CEJ
• Number :

CEJ- 30/mm Occlusal -10/mm

• Course – fairly regular

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Perikymata on enamel surface�

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• Enamel rod ends are concave
• Vary in depth and shape
• Cervical - Shallow Incisal /occlusal - Deep

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• pits 1-1.5 µm Enamel caps -elevations 10-15µm
• Larger elevations – enamel brochs

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• Cracks - narrow fissure like structures on surface

- Outer edges of enamel lamellae

• Extends for varying distances along the surface

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ENAMEL CUTICLE

(Nasmyth’s membrane/ primary enamel cuticle)

• Delicate membrane covering the entire crown of the newly erupted tooth
• Soon removed by mastication
• Basal lamina found beneath most of the epithelia
• Secreted by ameloblast when enamel formation is completed
• Protects the surface from resorptive activity

ENAMEL PELLICLE

• Apparently precipitate of salivary proteins
• This forms within hours after an enamel surface is mechanically cleaned.
• Within a day or two ----- colonized ----- Bacterial plaque.

AFIBRILLAR CEMENTUM – cervical area coverd

• Continuous with the cementum and mesodermal in origin
• Secreted after the epithelial enamel organ retracts from cervical region during tooth development.

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ENAMEL LAMELLAE

• Thin leaf like structure that extend from enamel surface towards DEJ, may extend to and some time penetrate into the dentin.
• Contain organic material but little mineral content
• In G/S Confused with cracks caused by grinding.
• Develop in planes of tension
• Rod crossing such a plane – may not fully calcify

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3Types:

Type A: Poorly calcified rod segments

Type B: Degenerated cells.

Type C: Cracks are filled with organic matter

presumably arising from the saliva.

• Type C more common
• A – restricted to enamel B&C –may reach to dentin

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• Lamellae may be site of weakness-may form a road of entry to bacteria that initiate caries.

ENAMEL TUFTS

• Narrow ribbon like structure, arises at DEJ and reach into the enamel about 1/5^th of 1/3^rd of its thickness.

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• Resemble tufts of grass when viewed in G/S

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• Hypo mineralized enamel rods and interprismatic substance.

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• Extend in the direction of long axis of crown, so better viewed in horizontal sections

ENAMEL SPINDLE

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• Odontoblastic processes pass across the DEJ into enamel.
• Many are thickened at their ends and termed as enamel spindles
• Direction corresponds to that of ameloblasts
• At right angles to dentin
• Hypomineralized structure

DENTINOENAMEL JUNCTION

• Surface of dentin at DEJ is pitted
• In to shallow depressions of dentin fit round projections of Enamel
• Firm hold of the Enamel cap on the dentin
• In sections appear as scalloped
• Convexities of the scallops are directed towards the dentin.
• Preformed before development of hard tissue

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