Dental Enamel

Question 1

What does the enamel do

Answer 1

• Forms outer covering of tooth
• Modifies colour of tooth

Question 2

Why are younger teeth whiter

Answer 2

Less translucent enamel

Question 3

Where is enamel thickest

Answer 3

Over cusps and incisal edges

Question 4

Where is enamel thinnest

Answer 4

At cervical margin

Question 5

How does enamel thickness evolve with time

Answer 5

Thickness declines gradually to become a very thin layer at the cervical margin

Question 6

What is the composition of enamel

Answer 6

Almost pure mineral - hydroxyapatite

Question 7

What are the physical properties of enamel

Answer 7

• Very hard due to high mineral content & its unique microstructural organisation
• Withstand forces from mastication
• High abrasion resistance so it wears down slowly
• Cannot be repaired or replaced
• Brittle so it depends on dentine for resilience

Question 8

What proteins comprise the matrix of immature enamel

Answer 8

• Amelogenin
• Ameloblastin
• Enamelin

Question 9

What are the chemical properties of human enamel

Answer 9

• Hydroxyapatite in enamel forms larger crystalites
• Crystalites are long, ribbon-like
• Tightly packed with pores

Question 10

How are crystallites grouped

Answer 10

Grouped as prisms - some form the interprismatic enamel

Question 11

Where do enamel spindles arise

Answer 11

At the ADJ, particularly around the cusps of teeth where most crowding of odontoblasts occurs

Question 12

What are enamel tufts

Answer 12

• Hypomineralised structures coming from the ADJ
• Tufts are spaces between prisms that contain the enamel protein ‘tuftelin’

Question 13

What are enamel lamellae

Answer 13

• Fine cracks in the surface of enamel
• Extend from surface of enamel to ADJ

Question 14

When and why are enamel lamellae formed

Answer 14

• During enamel development
• Due to incomplete maturation of enamel development or stress cracks

Question 15

Describe the structure of the newly erupted outer enamel

Answer 15

Non-prismatic

Question 16

Why is surface enamel more highly mineralised

Answer 16

Absence of prism boundaries

Question 17

Whats the advantage of surface enamel containing more fluoride than subsurface enamel

Answer 17

• Increased density
• Increased hardness
• Decreased solubility in comparison to subsurface enamel

Question 18

Whats the advantage of surface enamel being aprismatic

Answer 18

• Not subject to abrasion
• Less porous
• Less susceptible to acid dissolution

Question 19

Explain the Perikymata Grooves

Answer 19

Fine ridges resulting from the termination of the incremental striae of Retzius on the enamel’s surface

Question 20

Describe the sheets of enamel prisms forming the Hunter-Schreger bands

Answer 20

• Prisms are grouped into sheets of 10-13 layers, following a sinusoidal path
• Groups of prisms above and below them going in different directions

Question 21

Explain how the optical effect (Hunter-Schreger bands) are formed

Answer 21

Periodic changes in the direction of prism sheets

Question 22

Why are Hunter-Schreger bands visible

Answer 22

Different bands of prisms transmit light in different directions

Question 23

Whats the advantage of the complex pattern of prisms

Answer 23

Makes enamel resistant to a fracture

Question 24

What happens to enamel as age increases

Answer 24

Becomes progressively thinner due to tooth surface loss

Question 25

Why does the tooth darken as enamel age increases

Answer 25

Enamel becomes thinner + reduced translucency of tooth

Question 26

Why does enamel become less permeable with age

Answer 26

- Microporosity reduces - less spaces between crystallites - Crystals acquire more ions - Crystals increase in size

Question 27

What dissolves enamel mineral

Answer 27

Acids produced by plaque biofilm

Question 28

Where do early lesions develop and where do they progress

Answer 28

- Develop at the surface of enamel - Progress through the tissue following the orientation of prisms

Question 29

What does the microporus prismatic structure allow acids to do?

Answer 29

Allows acids produced by plaque biofilm to penetrate surface enamel and begin dissolving enamel prisms and crystallites

Question 30

Where will acids penetrate more readily?

Answer 30

- Where there's **greater porosity** - May tend to progress down **paths provided by prism boundaries**

Question 31

Why is removal of unsupported enamel an important element in cavity preparation design

Answer 31

Caries penetrates to the underlying dentine, leaving overlying enamel unsupported and prone to fracture during mastication

Question 32

What can lead to microleakage

Answer 32

Fracture of unsupported enamel

Question 33

What happens to prisms during tooth preparation

Answer 33

Prisms are sectioned, cracked and pulled apart