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

Question 1

Where is enamel thick and thin on a tooth?

Answer 1

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

occlusal surfaces on cusp tips

Question 2

What structures of a tooth can regrow?

Answer 2

dentin and cementum

Question 3

What provides the support to enamel?

Answer 3

dentin - resilient

Question 4

Does enamel have a high or low tensile strength?

Answer 4

low - brittle

Question 5

Where is the hardest enamel found?

Answer 5

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

Question 6

What layer of enamel is most mineralised?

Answer 6

the surface

Question 7

What is the gradient of hardness and density in the

Answer 7

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

Question 8

What colour is young enamel vs old enamel?

Answer 8

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

Question 9

What is the percentage breakdown of enamel?

Answer 9

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

Question 10

What is the principal mineral component of enamel?

Answer 10

calcium hydroxypapatite

Question 11

What are examples of organic substances in enamel?

Answer 11

50-90%

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

Question 12

What shape do hydroxyapatite crystals form?

Answer 12

hexagonal

Question 13

What do you call a crystal of hydroxyapatite?

Answer 13

crystallite

Question 14

What are the dimensions of an enamel hydroxyapatite crystal?

Answer 14

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

Question 15

What makes up each hydroxyapatite crystal unit?

Answer 15

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.

Question 16

What units make a hydroxyapatite crystal?

Answer 16

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

Question 17

Can there be substitutions in the hydroxyapatite crystal?

Answer 17

YES

Question 18

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

Answer 18

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

Question 19

How does a fluoride substitution effect crystallites?

Answer 19

Fluoride’s incorporation in the crystal inhibits caries.

Question 20

How does a carbonate substitution effect crystallites?

Answer 20

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

Question 21

What is the presence of water in enamel relate to?

Answer 21

Water presence is related to the porosity of the tissue.

Question 22

Where might water be located in enamel?

Answer 22

Might be present between the crystals surrounding the organic component.

Might be trapped within crystalline defects forming a hydration layer.

Question 23

What can travel through the water component?

Answer 23

fluoride ions

Question 24

What percent of the mature enamel is organic matrix?

Answer 24

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

Question 25

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

Answer 25

amelogenins and non-amelogenins (enamelins).

Question 26

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

Answer 26

Tufts

Question 27

Where are tufts located?

Answer 27

the dentine-enamel junction

Question 28

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

Answer 28

rich in carbohydrates

Question 29

What may lipids in enamel represent?

Answer 29

May represent remnants of cell membranes.

Question 30

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

Answer 30

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

Question 31

What is protein is the bulk of developing enamel matrix?

Answer 31

amelogenin

Question 32

What produces amelogenin?

Answer 32

ameloblasts

Question 33

Are amelogenins hydrophobic or hydrophilic?

Answer 33

hydrophobic tend to aggregate into clumps.

Question 34

Do amelogenins spread throughout the entire enamel?

Answer 34

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

Question 35

What does the gel matrix allow?

Answer 35

gel matrix through which molecules and ions spread readily.

Question 36

What aids in the formation of large crystals?

Answer 36

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.

Question 37

What is an example of a non-amelogenin?

Answer 37

tuftelin

Question 38

What do the non-amelogenins derive form?

Answer 38

May be derived from plasma albumin or aminoblasts themselves Contain distinct components secreted by ameloblasts.

Question 39

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

Answer 39

possibly