(2) Anatomy and Histology of the Periodontium - Enamel (A) Flashcards

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1
Q

Where is enamel thick and thin on a tooth?

A

Thickness varies from up to 2.5mm (1.3mm in primary) over cusps to feather edge at cervical margins.

occlusal surfaces on cusp tips

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2
Q

What structures of a tooth can regrow?

A

dentin and cementum

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3
Q

What provides the support to enamel?

A

dentin - resilient

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4
Q

Does enamel have a high or low tensile strength?

A

low - brittle

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5
Q

Where is the hardest enamel found?

A

Surface enamel is harder, denser and less porous than subsurface enamel.

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6
Q

What layer of enamel is most mineralised?

A

the surface

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7
Q

What is the gradient of hardness and density in the

A

Hardness and density decrease from the cusp tips to the cervical margins.

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8
Q

What colour is young enamel vs old enamel?

A

Young enamel appears white turning to a more yellow appearance as translucency increases with age.

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9
Q

What is the percentage breakdown of enamel?

A

Enamel is composed of 96% inorganic components, 2% organic component and 2% water by weight.

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10
Q

What is the principal mineral component of enamel?

A

calcium hydroxypapatite

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11
Q

What are examples of organic substances in enamel?

A

50-90%

Free amino acids, small molecules, peptides and large protein complexes (amelogenins and non-amelogenins)

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12
Q

What shape do hydroxyapatite crystals form?

A

hexagonal

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13
Q

What do you call a crystal of hydroxyapatite?

A

crystallite

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14
Q

What are the dimensions of an enamel hydroxyapatite crystal?

A

Enamel hydroxyapatite crystals are about 70nm in width, 25nm thick and of great length (almost the full thickness of enamel).

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15
Q

What makes up each hydroxyapatite crystal unit?

A

One hydroxyl group surrounded by 3 calcium ions which are surrounded by 3 phosphate ions. Six calcium ions in a hexagon enclose the phosphate ions.

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16
Q

What units make a hydroxyapatite crystal?

A

The crystal is made of a repetition of those planes of ions side by side in stacked layers.

17
Q

Can there be substitutions in the hydroxyapatite crystal?

A

YES

18
Q

What effect does the substitutions in hydroxyapatite crystals have on teeth?

A

The ions present in enamel may influence dental caries by affecting the dissolution of the apatite crystals and/or affecting remineralisation.

19
Q

How does a fluoride substitution effect crystallites?

A

Fluoride’s incorporation in the crystal inhibits caries.

20
Q

How does a carbonate substitution effect crystallites?

A

Carbonate’s incorporation in the crystal promotes the carious attack.

21
Q

What is the presence of water in enamel relate to?

A

Water presence is related to the porosity of the tissue.

22
Q

Where might water be located in enamel?

A

Might be present between the crystals surrounding the organic component.

Might be trapped within crystalline defects forming a hydration layer.

23
Q

What can travel through the water component?

A

fluoride ions

24
Q

What percent of the mature enamel is organic matrix?

A

Mature enamel 1-2%; varies from 0.05% to 3% depending on the regularity of the crystals.

25
Q

What are the larger protein complexes found in the organic matrix?

A

amelogenins and non-amelogenins (enamelins).

26
Q

What protein of the organic matrix is at the highest concentration?

A

Tufts

27
Q

Where are tufts located?

A

the dentine-enamel junction

28
Q

In the organic matrix, what do components with larger molecular weights contain?

A

rich in carbohydrates

29
Q

What may lipids in enamel represent?

A

May represent remnants of cell membranes.

30
Q

Do proteins and lipids account for more of the total enamel weight in mature or early enamel?

A

Proteins and peptides account for less than 2% of mature enamel weight and 25-30% of early enamel.

31
Q

What is protein is the bulk of developing enamel matrix?

A

amelogenin

32
Q

What produces amelogenin?

A

ameloblasts

33
Q

Are amelogenins hydrophobic or hydrophilic?

A

hydrophobic

tend to aggregate into clumps.

34
Q

Do amelogenins spread throughout the entire enamel?

A

They spread throughout the whole developing enamel resulting in a gel matrix through which molecules and ions spread readily.

35
Q

What does the gel matrix allow?

A

gel matrix through which molecules and ions spread readily.

36
Q

What aids in the formation of large crystals?

A

Amelogenins are Hydrophobic and tend to aggregate into clumps.

They spread throughout the whole developing enamel resulting in a gel matrix through which molecules and ions spread readily.

This helps in the formation of large crystals.

37
Q

What is an example of a non-amelogenin?

A

tuftelin

38
Q

What do the non-amelogenins derive form?

A

May be derived from plasma albumin or aminoblasts themselves

Contain distinct components secreted by ameloblasts.

39
Q

Do the non-amelogenins have a role in mineralisation of enamel?

A

possibly