Histology Of Enamel

Question 1

Embryonic origin of enamel

Answer 1

Ectoderm

Question 2

Inorganic mineral content of enamel composition

Answer 2

96%
Majority - calcium hydroxyapatite
Minority - carbonate, fluoride

Question 3

Components of calcium hydroxyapatite

Answer 3

Calcium
Phosphate
Hydroxyl

Question 4

Organic mineral content of enamel composition

Answer 4

4%
Fibrous collagen material
Water
Some proteins

Question 5

Overview of enamel structure

Answer 5

• Enamel rods (prisms)
• Interrods
• Crystallites (calcium hydroxyapatite)
• Link to amelogenesis
• Incremental lines
• Prismless enamel (rod-less)
• Dento-enamel junction and microscopic features.

Question 6

Key structural unit of enamel

Answer 6

Enamel rods (prisms)

Question 7

What does each enamel rod contain and how are they structured?

Answer 7

Millions of calcium hydroxyapatite crystallites.
Tightly packed with a head and tail in keyhole shape.

Question 8

Orientation of head and tail of enamel rods

Answer 8

Head - usually towards occlusal/incisal surface.

Tail - usually towards cervical region.

Question 9

Interrod

Answer 9

Tail of enamel rod

Question 10

What surrounds each rod and interrod?

Answer 10

Sheath of organic material

Question 11

What runs within the the enamel rods and what’s their orientation

Answer 11

Enamel crystallites
In the head runs parallel with long axis of rod
In the tail they diverge slightly.

Question 12

What’s the significance of the pattern of crystallites within the rod

Answer 12

Adds to the strength of enamel

Question 13

Amelogenesis

Answer 13

Process of enamel formation.
Results in incremental lines.

Question 14

What forms the structure of enamel rods

Answer 14

Ameloblasts
1 ameloblast forms 1 enamel rod

Question 15

Lifecycle of ameloblasts

Answer 15

Only live for as long as the enamel is forming. They move into function of protection during eruption, this ends their life cycle.

Question 16

Strip of retzius

Answer 16

Growth rings in the ground sections on enamel under a microscope

Question 17

Perkymata

Answer 17

Edge of the stria of retzius that is clinically visible on the enamel surface showing where the incremental lines reach the labial and buccal surfaces.

Question 18

Structure of enamel rods at the cusps

Answer 18

Twisted forming gnarled enamel, adds to overall strength

Question 19

Structure of rods at dentoenamel junction

Answer 19

Perpendicular to the dentine

Question 20

Areas of princess/aprismatic enamel

Answer 20

Very first and last formed enamel usually has no prism structure where the crystals are parallel to surface.

Question 21

Structure of prismless enamel

Answer 21

30 microns wide
Includes more fluoride and carbon
Seen in primary dentition and 70% of permanent dentition. (Greatest in cervical regions)

Question 22

Clinical significance of primless enamel

Answer 22

Can interfere with optimal etching

Question 23

When does the dentine enamel junction form and microscopic appearance

Answer 23

Once dentinogenesis and amelogenesis have started.
Scalloped appearance.

Question 24

Microscopic features at the dentine-enamel junction

Answer 24

Enamel tuft
Enamel spindles

Question 25

Structural features at enamel surface and how they form

Answer 25

Lamella.
Appear as cracks in enamel - developmental defects.
Result of ameloblast ceasing production of enamel.

Question 26

Functions of enamel

Answer 26

Protect
Eating
Ion exchange
Inability to repair or feel injury
Smile

Question 27

How does the function of enamel link to its structure?

Answer 27

• Protect tooth/pulp; covers entire tooth crown, hardest biological tissue.
• Eating; thickest at cusp/occlusal/incisal surfaces.
• Inability to repair or feel injury; inert tissue.
• Able to re/demineralise; highly mineralised tissue.
  Smile; white translucent crystalline.

Question 28

What does the exchange of ions cause in enamel over the life course?

Answer 28

Reduced permeability

Question 29

The critical pH level of enamel

Answer 29

5.5

Question 30

Acidic conditions the balance favours

Answer 30

Demineralisation

Question 31

Alkaline conditions the balance favours

Answer 31

Remineralisation
Enables uptake of fluoride and calcium phosphate.

Question 32

What substance in the mouth is alkaline and favours remineralisation?

Answer 32

Saliva

Question 33

Critical pH level of fluorapatite and its relevance

Answer 33

4.5; lower than hydroxyapatite and therefore more resistant to acids and demineralisation.

Question 34

How is the composition and structure of enamel in clinical prevention?

Answer 34

• Inert; no living cell, unable to feel injury, we need to be able to risk assess and detect early caries/changes.

Question 35

Local disturbances

Answer 35

Affect individual teeth
(Trauma)

Question 36

Systemic disturbances

Answer 36

Affect all teeth forming at the time
(Fluorosis, tetracycline exposure, MIH)

Question 37

Genetic factors

Answer 37

May affect all teeth
(Amelogenesis imperfecta)

Question 38

Neo-natal line in enamel

Answer 38

Exaggerated line that shows distinction between enamel that formed before and after birth.
(Usually reflects disturbance in amelogenesis at birth)

Question 39

Other exaggerated lines in enamel

Answer 39

Reflect systemic disturbances during amelogenesis.
(Fever, tetracycline staining)

Question 40

Defects during amelogenesis can result in?

Answer 40

Molar incisor hypomineralisation.
(Softer enamel, more prone to caries)