Enamel

Question 1

State 3 Properties of Enamel

Answer 1

brittle - if not supported by dentine, it fractures = cavitation
withstands shearing hard forces
highly mineralised

Question 2

Consituents of Enamel

Answer 2

95% pure mineral - hydroxyapatite
4% water
1% organic material - mainly non-collagenous protein

Question 3

Hydroxyapatite - structure and length

Answer 3

prisms and rods
- perpendicular to ADJ
5micrometer diameter

Question 4

What Pattern does the Daily Incremental Lines Follow?

Answer 4

Cross-striations in a circadian rhythm
- dark and light lines in intervals of 3-6micrometer

Question 5

What is the Brown Striae of Retzius?

Answer 5

less frequent incremental lines
- irregularly spaced at the cusp
- associated with perikymata depressions
= able to provide space for diffusion pathways

Question 6

What are Hunter-Shreger Bands?

Answer 6

banding pattern when there are periodic changes in direction of prism sheets
-diazones = prisms are sectioned transverse
- parazones = prisms are sectioned longitudinally

Question 7

What is the Appearance of the ADJ, and two characteristics?

Answer 7

scalloped appearance
- aids retention of enamel on dentine
- resist shearing by forces

Question 8

Give 3 other Structural Features of the Enamel

Answer 8

Spindles
Tufts
Gnarled Enamel

Question 9

Describe Spindles and how they Relate to Enamel Tubules

where does it originate? appearance? penetrations?

Answer 9

originate at ADJ around cusps - where there is a lot of odontoblast crowding

• dark, club shaped
• penetrate 25micrometer in enamel
• not aligned with prisms

enamel tubules
= when odontoblast processes disrupt spindle and elongate into enamel
= creates a void

Question 10

Describe Tufts

what is it? where does it orginiate? appeareance? protein? thickness?

Answer 10

• when residual enamel protein has collected between prisms
• originate at ADJ
• appears like tuft of grass
• sinusoidal path to the surface
• contain tuftelin enamel protein - high content of mature enamel
• 1/3 thickness of enamel

Question 11

What is Gnarled Enamel? What are 2 Benefits?

Answer 11

when prisms are disordered at cusps

= increase resistance to fracture and occlusal masticatory forces
= regular changes of direction

Question 12

What are the Zones of Enamel Caries from surface to pulpal

Answer 12

**surface zone - under the plaque biofilm
- lacks fluoride concentration
- 1-10% mineral loss - partial demineralisation
- calcium and phosphate ions release here to encourage remineralisation
- disrupted when lesions penetrate into dentine

**Body of lesion
- highest porosity
- most affected
- 60-70% mineral loss before cavitation

**Dark zone
- remineralisation, high protein = 5-20% mineral loss
- reflects light - appears unequal

** Transulcent zone
- least affected
- less than 1% mineral loss
- ions dissolve out - allows re-precipitation
- uniform pore size

Question 13

Describ the Outermost Enamel

Answer 13

Porous

Question 14

What are some Developmental Defects of Enamel

Answer 14

irregular fissures and micro-pores

Question 15

How does the Microstructure Affect Carious Process? (4)

Answer 15

• outmost enamel = porous
• developmental defects - fissure and pores
• opening striae of Retzius at surface via perikymata grooves = diffusion pathway
• inter-crystalline spaces - filled with water - diffusion pathway

Question 16

The Mechanism of Caries Progression through Enamel and Dentine

Answer 16

1.plaque layer forms on enamel

2.release of organic acids by bacteria

3.dissolution - exposure by acid
= irregular crystal outline
= demineralisation
= destruction in prism cores

4.spreads along ADJ
5. dentinal tubules become narrow and sclerosed
6. reactionary dentine on pulpal wall
7. enamel surface cavities
8. bacteria invades lesion and penetrate dentinal tubules

• EQM between ions in plaque and hydroxyapatite
• acid favours plaque

Question 17

Define Caries

Answer 17

A localised, chemical dissolution of tooth surface brought about by metabolic activity in a microbial deposit/dental biofilm, covering a tooth surface at any given time

Question 18

In an Enamel Caries Lesion, How does the Early Stage, Later Stage Appear, and What is the Name of the Stain?

Answer 18

Early = opaque white spots
- subsurface loss of mineral due to acid dissolution

Later = cavity and exposed dentine

Stain = brown spot lesions

Question 19

What is Occult/Hidden Caries, why does it happen?

Answer 19

occlusal surface appears to be intact but shows radiolucencies in dentine, it derives from occlusal/pit caries

• enamel has a higher fluoride conc, which increases resistance to carious breakdown

Question 20

How does Occlusal/Pit Enamel Caries Lesion Occur and Proceed?

Answer 20

• food debris and plaque accumulation in fissure
• acid
• dissolution begins on walls rather than the base
• penetrates perpendicular towards ADJ
  = cavitation
• occurs without apparent break in enamel surface