Enamel

Question 1

What is the hardest tissue in the body?

Answer 1

• Enamel

Question 2

What are the regional variations of enamel? (2 points)

Answer 2

• Surface enamel is more mineralised and harder than deeper enamel
• Hardness decreases from cusp tip/incisal edge to cervical region

Question 3

What is enamel maturation?

Answer 3

• The process of changing from about 30% inorganic mineral in enamel matrix of the teeth to the 96% inorganic content in mature enamel.
• The maturation is accomplished by the ameloblast cells over a long period, with a decrease in water and organic content, and an increase in mineral content and size or density of hydroxyapatite crystals.
• The final stages of enamel maturation occur after the tooth has erupted into the oral cavity

Question 4

What is the basic unit of enamel?

Answer 4

• Rod/prism

Question 5

What are the dimensions of enamel rods?

Answer 5

• 5micrometers x 2.5mm

Question 6

Where do enamel rods run from?

Answer 6

• ADJ to the surface

Question 7

How many HA crystallites do enamel rods contain?

Answer 7

10^6

Question 8

Where are enamel rods perpendicular?

Answer 8

• When they are closest to the ADJ

Question 9

Where are enamel rods parallel?

Answer 9

• When nearest to the surface of the tooth, which helps keep the enamel from splitting and ensures that the surface of the tooth is smooth

Question 10

Why do long, parallel enamel rods have cross striations?

Answer 10

• Consequence of the growth of the rod -> daily growth is approx. 4 micrometres

Question 11

How far apart are brown transverse striae?

Answer 11

• 25-35 micrometres apart

Question 12

When are brown transverse striae formed?

Answer 12

• At weekly intervals

Question 13

How does enamel rod structure arise?

Answer 13

• From variations in orientation of crystallites

Question 14

Are ‘head’ and ‘tail’ regions of enamel rods composed of the same HA crystals?

Answer 14

• Yes

Question 15

What is the HA content in enamel?

Answer 15

• 95% weight

- 90% volume

Question 16

What is the water content in enamel?

Answer 16

• 4% weight

- 5-10% volume

Question 17

What is the organic matrix content in enamel?

Answer 17

• 1% weight

- 1-2% volume

Question 18

What is contained within the organic matrix of enamel? (5 points)

Answer 18

• Proteins
• Amelogenins
• Enamelins
• Peptides
• AA’s

Question 19

After a restoration has ben placed, what will happen to the composition of enamel? (2 points)

Answer 19

• Will loose water

- Will loose organic matrix

Question 20

What part of enamel gives it the ability to withstand forces?

Answer 20

• The organic matrix

- ‘minor protein component regulates the nanomechanical properties of enamel’

Question 21

Where are crystallites deposited in relation to the ameloblast membrane?

Answer 21

• At right angles

Question 22

What is the tomes process?

Answer 22

• A histological landmark identified on an ameloblast, cells involved in the production of tooth enamel.
• During the synthesis of enamel, the ameloblast moves away from the enamel, forming a projection surrounded by the developing enamel.
• Tomes processes are those projections
• They are located on the secretory basal end of the ameloblast

Question 23

What shape are crystallites?

Answer 23

• Hexagonal

Question 24

In which area are crystallites the largest: enamel, dentine, cementum or bone?

Answer 24

• Enamel

Question 25

How much of the enamel rod do HA crystallites go through?

Answer 25

- A small portion 

Question 26

Will you see enamel in ground sections histologically?

Answer 26

- Yes, mineral present (no soft tissues)

Question 27

Will you see enamel in decalcifies sections histologically?

Answer 27

- No, (will only see soft tissues)

Question 28

Enamel rods run in a sinusoidal course: what does this mean?

Answer 28

- Have an s-shape arrangement 

Question 29

Do adjacent groups of enamel rods have the same or different arrangements?

Answer 29

- Different

Question 30

What are Hunter-Schreger bands found in enamel?

Answer 30

- The periodic orientation of enamel rods causes periodic orietation - Alternating light and dark lines seen in enamel of the tooth that begin at the ADJ and end before they reach the enamel surface, they may represent areas of enamel rods cut in cross-sections dispersed between areas of rods cut longitudinally

Question 31

Where are Hunter-Schreger bands absent from in enamel?

Answer 31

- In the outer enamel 

Question 32

What is gnarled enamel?

Answer 32

- Enamel under the cusp of a tooth characterised by twisting. Intertwining groups of enamel rods, thought to resist shearing forces

Question 33

What are 'brown striae of Retzius'?

Answer 33

- Prominent lines that run obliquely across the prisms to the surface - They represent the successive positions of enamel forming front

Question 34

What is the neonatal line?

Answer 34

- A particularly marked striae that is formed at birth - It reflects the metabolic changes at birth - Prisms change both direction and thickness at this event

Question 35

What is the name of the junction between enamel and dentine?

Answer 35

- The amelo-dentinal junction 

Question 36

What are enamel tufts?

Answer 36

- Less mineralised areas of enamel in the inner third of enamel adjacent to the ADJ. They resemble tufts of grass 

Question 37

What are enamel lamella?

Answer 37

- Incomplete maturation of groups of prisms - 'fault' line extending through enamel thickness 

Question 38

What are enamel spindles?

Answer 38

- Odontoblast processes extending into enamel