Enamel

Question 1

what supports enamel?

Answer 1

dentine
needs this to work properly
without it will fail

Question 2

give characteristics of enamel

Answer 2

• hardest tissue in body
• brittle
• resists abrasion
• variable thickness
• translucent
• transparency increases with mineralisation

Question 3

why is enamel not as thick in primary teeth?

Answer 3

meant to be in the mouth for a shorter period of time

Question 4

compare surface enamel to deeper enamel

Answer 4

surface enamel is more mineralised and harder than deeper enamel
[this is only true of a tooth that hasn’t just erupted as over time enamel becomes harder]

Question 5

how does enamel thickness vary within a tooth

Answer 5

hardness decreased from cusp tip / incisal edge to cervical region
this makes sense as the incisal edge needs to be harder for biting etc

Question 6

what is the basic unit of enamel

Answer 6

enamel rod / prism

Question 7

what is the width x length of an enamel rod

Answer 7

5 micrometres x 2.5mm

Question 8

where are rods in enamel?

Answer 8

they run from the ADJ to the surface
orientation varies within and along the enamel
c

Question 9

how many hyrdoxyapattite crystals does 1 rod contain?

Answer 9

over 10 to the power of 6 crystals

Question 10

what are long parallel rods

Answer 10

cross striations in rod due to a consequence of growth when created
due to daily growth [approx 4 micrometres]

Question 11

what are brown transverse striae

Answer 11

25-35 micrometres apart

formed at weekly intervals

Question 12

what is the purpose of acid etching the enamel

Answer 12

not intended to actually remove rods

want to make the surface uneven to help make a connection between the enamel and the material

Question 13

what is the composition of enamel?

Answer 13

• Hydroxyapatite (HA)
		○ 95% weight
		○ 90% volume 
	• Water
		○ 4% weight 
		○ 5-10% volume
	• Organic matrix 
		○ 1% weight
		○ 1-2% volume 
		○ Proteins 
			§ Amelogenins 
			§ Enamelins 
			§ Peptides 
			§Amino acids
% is for healthy enamel only

Question 14

what regulates the nanomechanical properties of enamel?

Answer 14

minor protein components - part of the organic matrix

Question 15

what ways can forces be organised?

Answer 15

vertically or horizontally

Question 16

when is crystallite orientation determined

Answer 16

during enamel formation

Question 17

how are crytallites deposited?

Answer 17

at right angles to ameloblast membrane

Question 18

what is the proposed scheme for the development of crystallites?

Answer 18

• Ameloblasts will create a globular structure in which the inner portions can be hyperconcentrated in terms of calcium and phosphate = supersaturation
• Proteins allow supersaturation of calcium but allow it in a very specific arrangement that creates the perfect form for the formation of the crystallites
• You need to have access to calcium phosphate for the crystal to grow on its own
• Cocoon protecting the calcium phosphate needs to be removed for crystal to form
• 2 stages of maturation
○ Mineralisation in the first stage is around 30%
○ We require breakdown of amelogenins
○ Amelogenesis imperfecta is condition linked to lack of breakdown of amelogenins
• Then crystal grows to full potential

Question 19

what are Hydroxyapaptite (HA) crystals?

Answer 19

• HA: Ca10(PO4)6(OH)2
  
  • Hexagonal crystallites
  • 70 nm x 25 nm x up to 1 micrometre long
  • Larger in enamel that in dentine, cementum or bone

Question 20

ion substitution in HA crystals happen by what?

Answer 20

• Ion substitutions by:
	              Mg2+, CO32-, F-
Mg = metal
carbonate = phosphate arrangement
F = negative arrangement
mix of these

Carbonated apatite = not perfect HA
When tooth is erupted, substitution occurs over time

Enamel matures in the mouth to have carbonated part removed
= becomes proper HA

Question 21

what does the maturation of enamel need?

Answer 21

fluoride to be present

demineralisation and remineralisation process occurring

Question 22

what does traditional histology of enamel use?

Answer 22

• ground sections
  > mineral present, no soft tissues
• decalcified sections
  > no mineral, soft tissues

Question 23

what is the shape of enamel rods?

Answer 23

sinusoidal course
‘S’ shape
not straight

Adjacent groups of rods have different orientations

Periodic orientation causes banding patterns (Hunter-Schreger bands)

Question 24

what are Hunter-Schreger bands?

Answer 24

○ Rod periodic orientation
○ Absent in outer enamel
○ Rods are not arranged in a parallel arrangement

Question 25

where would you find gnarled enamel?

Answer 25

○ Cusps
§ Greater concentration of the rods
§ This is to withstand the distribution of forces

Question 26

name incremental lines

Answer 26

brown striae of retzius
perikymata
neonatal line (not common)

Question 27

what features can be found at the ADJ?

Answer 27

• Enamel tufts
○ Hypo-mineralised regions due to residual matrix protein at prism boundaries

• Enamel lamella
○ Incomplete maturation of groups of prisms - ‘fault’ line extending through enamel thickness

• Enamel spindles
○ Odontoblast processes extending into enamel
○ Rare to see

Question 28

why are early lesions often found in fissures in the enamel?

Answer 28

limited ability to buffer in these areas

Question 29

how does enamel structure influence caries?

Answer 29

• Concentration of rods cuspally
• Arrangement of rods
  ○ Caries is not a one fits all process
  ○ Shape of carious lesion depends on the type of arrangement of the rods