ENAMEL Flashcards by ELIZA NICOLE ATA

the hard, outer
surface layer of
the teeth that
serves to protect
against tooth decay

ENAMEL

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hardest calcified tissue in the human body

ENAMEL

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Is the enamel harder or more mineralized at the surface

yes

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What is the color of the enamel

white to grayish-white, slightly yellow appearance only

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Is it translucent?

yes

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Does the enamel provide the shape and contour of the
crowns of teeth

yes

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Does the enamel act as semipermeable membrane

yes

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Is enamel a good conductor of both heat and electricity

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Is it vital and capable of regeneration

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Choose which part of the tooth is enamel thickest with 2.0-2.5mm

crest of cusps or incisal edges

fissures and pit facial, lingual
and interproximal surfaces

cervical margin

crest of cusps or incisal edges

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Choose which part of the tooth is enamel thinner with 1.0 – 1.5 m

crest of cusps or incisal edges

fissures and pit facial, lingual
and interproximal surfaces

cervical margin

fissures and pit facial, lingual
and interproximal surfaces

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Choose which part of the tooth is enamel thinnest with <100µm

crest of cusps or incisal edges

fissures and pit facial, lingual
and interproximal surfaces

cervical margin

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What is the inorganic material of enamel?

Hydroxyapatite crystals
Varying amount of carbonates
Trace elements (vanadium, manganese, selenium, molybdenum &
strontium)

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What is the organic material of enamel?

Soluble and insoluble proteins:
Amino acid
Predominantly enamelins

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immature enamel

AMELOGENNINS

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mature enamel

ENAMELINS

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Basic structural unit of enamel

ENAMEL RODS

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Enamel rods are first described as

hexagonal or prism-like

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Enamel rods are more appropriately described as a

cylindrical rod

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Enamel rod has a pattern of

“horseshoe” or
“paddle-shaped” or
“racquet-shaped” with a head and
tail

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Number of enamel rods

5 – 12 millions

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Direction of enamel rods

Run in oblique direction and wavy
course

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Length of enamel rods

greater than the thickness of enamel

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Diameter average of enamel rods

4 µm

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Appearance of enamel rods

clear crystalline appearance

Cross-section of enamel rods

hexagonal, round, oval, or fish scales

Submicroscopic Structure Of Enamel Rods Shape?

Keyhole or paddle-shaped.

Submicroscopic Structure Of Enamel Rods Separated by?

interrod substance

Enamel rods in breadth?

5 µm

Enamel rods in length?

9 µm

Bodies of enamel rods located

near the occlusal or incisal surface

Tails of enamel rods point direction

cervically

- the rod’s surface - contain more enamel protein or organic matrix and recystallized hydroxyapatite crystals - more acid-resistant than other regions

ENAMEL ROD SHEATH

- cements the rods together - More calcified than the rod sheath - Less calcified than the rod itself

INTERROD ENAMEL

Direction of enamel rods in general

perpendicular to the surface or the dentin

Direction of enamel rods near the cusp tip

nearly vertical

Direction of enamel rods under pits and fissures

tent-like manner

Direction of enamel rods on proximal or sides

nearly horizontal

Direction of enamel rods cusp or incisal

vertical

Direction of enamel rods cervical

mainly horizontal or obliquely inclined

- Rods appear twisted around each other in a seemingly complex arrangement - offers the greatest resistance to the cusp and incisal areas where most of the forces are applied

GNARLED ENAMEL (GNARLED ENAMEL ROD)

- Are an optical phenomenon produced solely by changes in rod direction - thought to be functionally adapted structures for the prevention of enamel cracking during chewing

BANDS OF HUNTER-SCHREGER

seen most clearly in longitudinal ground section viewed by reflected light

Hunter-Schreger Bands

- found in the inner 4/5 of the enamel - appear as dark and light alternating zones

Hunter-Schreger Bands

*dark lines crossing the rods * indicate a daily (or circadian) variation in the secretory activity of the ameloblasts * periodic bands or cross striations * 4 micrometer * SEM reveals alternating constrictions and decreasing expansions of the rods

TRANSVERSE STRIATION

o growth lines o brownish bands in ground section o Reflects variation in structure and mineralization o etiology: * Periodic bending of enamel rods * Variation in organic structure * Physiologic calcification rhythm - weekly (or circasepttimanian)

INCREMENTAL LINES (STRIAE) OF RETZIUS

Does the increment lines of retzius reach the outer enamel surface?

What shape does the incremental lines of retzius form?

horse-shoe shaped

Is the increment lines of retzius prominent in human permanent teeth

Yes

When is the increment lines of retzius rare?

prenatal enamel

In cross section, the lines of retzius appears as __________

Concentric rings

* These grooves represent the lines of Retzius as they meet the surface enamel

Perikymata/Imbrication lines of Pickerill

a pattern of line recognizable to the unaided eye on enamel surface of sound, freshly erupted tooth

Perikymata/Imbrication lines of Pickerill

* shingle-like overlapping arrangement * closely spaced - cervical margin * further apart - mid-coronal region * absent - cusp tips and incisal edges

Perikymata/Imbrication lines of Pickerill

- an accentuated line – brownish line - reflects the marked physiologic changes occurring at birth - most primary teeth and permanent central incisors have these

neonatal line

▪Originate at the dentinoenamel junction ▪about 1/5 to 1/3 of the thickness of the entire enamel ▪They resemble tufts of grass growing out of a root ▪Composed of hypomineralized enamel rods, interrod enamel and organic material—enamelin

ENAMEL TUFTS

* visible cracks on the surface of the enamel * confused with cracks caused by grinding (decalcification) * represent site of weakness * are important as a pathway through enamel * function as a possible avenue for dental caries

ENAMEL LAMELLAE

* because enamel is highly mineralized, stress from breathing cold air or drinking cold beverages may cause small cracks to occur in enamel, especially where enamel is weakened by underlying caries

ENAMEL LAMELLAE

* extensions from dentinal tubules that penetrate the DEJ into the enamel * seen as black or dark irregular or spiral-shaped or club-shaped structures * are normally filled with dentinal fluid

ENAMEL SPINDLE

* their dark appearance is due to the presence of air and debris resulting from the preparation of the section * one of the factors that cause the hypersensitivity of the dentino-enamel junction

ENAMEL SPINDLE

* scalloped junctionthe concavities toward dentin

Dentino-Enamel Junction

Begin after a few micrometer of dentin have been deposited

AMELOGENESIS

Environmental Influences of Amelogenesis

* Nutrition * Calcium, phosphorus, protein, fluoride etc… * Hypoxia * Hyperthermia * Infection * Physical Determinants

Functional Stages of Amelogenesis

1. Morphogenetic Stage 2. Organization & Differentiation 3. Secretory Stage – synthesis of enamel 4. Maturation Stage 5. Protective Stage