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M3: Oral Biology > Enamel > Flashcards

Enamel Flashcards

1
Q

What is the composition of enamel by weight?

Dentine?

Cementum?

Bone?

A

Mineral: 96% Matrix: 2% Water: 2%

Dentine: 70%, 20%, 10%

Cementum: 65%, 23%, 12%

Bone: 60%, 25%, 15%

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2
Q

List some features of enamel:

A
  • epithelial product
  • 96% inorganic - hydroxyapatite
  • 2mm thick max
  • translucent
  • non-vital
  • hard (KHN 360-390)
  • brittle
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3
Q

What is the formula of hydroxyapatite?

A

Ca10(PO4)6(OH)2

  • OH ion surrounded by 3 Ca ions, surrounded by 3 PO4 ions, enclosed by 6 Ca ions
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4
Q
A
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5
Q

What is a ground section?

A
  • cut hard tissues, by a saw
  • 150 microns thick
  • not stained
  • light refracts
  • light reflects internally
  • hypomineralised areas (less mineralised) appear dark
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6
Q

What does the enamel structure consist of?

A
  • tightly packed hyydroxyapatite crystals
  • basic unit = enamel prism
  • prisms visible in: ground sections, scanning electron micrographs of acid etched enamel
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7
Q

How are keyhole shapes formed in enamel prisms?

What do they dots represent on a diagram?

Dashes?

A
  • due to the different orientations of hydroxyapatite crystals

Dots represent the prism core: tightly packed hydroxyapatite crystals

Dashes = prism shealth: boundary of clearly different crystal orientations, crystals less tightly packed, more space for organic components

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8
Q

Interesting features of the enamel prisms:

A
  • follow path of the ameloblasts ~ 90 degrees to ADJ
  • undulating/weaving course –> increases strength
  • cross striations, interval ~ 5 microns
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9
Q

Name this feature of the prisms?

Where is it most commonly seen?

A

Gnarled enamel: at the cusps/incisal edges, the prisms appear twisted around each other, giving more strength, minimising risk of fracture

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10
Q

What is the purpose of acid etching?

A
  • Gives micro-mechanical retention for bonding of resin materials
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11
Q

Where are enamel prisms? Are there any exceptions?

A
  • enamel prisms exist for the majjority of the enamel thickness

2 regions are aprismatic:

  • 1st formed (innermost) 5 microns
  • last formed (outermost) 30 microns

Bond strength of outer surface may be less than that of the enamel prism surfaces

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12
Q

Name this feature?

What does this feature look line as a cross section?

What can cause these lines to be exaggerated?

A

Incremental growth lines - ‘‘Striae of Retzius’’

  • appear as brown lines in enamel
  • represent where forming cells were at different times (roughly weekly growth)

Accentuated lines result from:

  • systemic disturbance e.g. illness
  • birth - Neonatal line, crowns forming at birth e.g. primary teeth and crown of 6s may be forming at birth
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13
Q

What happens when incremental line reach the surface?

A
  • Perikymata: shallow furrow where the striae reach the surface, plaque retentive factor
  • Imbrication Lines of Pickerill: ridges between perikymata
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14
Q

What are these dark lines?

A

Enamel spindles - extension of dentinal tubules into enamel, so found at ADJ, appear dark as full of water or air

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15
Q

What are these black lines?

A

Enamel tufts - hypomineralised local areas

Enamel lamellae - run from ADJ out to surface

  • developmental
  • aquired e.g. crack
  • preparation artefact e.g. tooth cracks when being cut onto slide
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16
Q

Where is enamel caries more likely to deleop in temr sof the enamel structure?

A

Prism shealth - periphery

  • less well packed crystals
  • space = pores containing water and organic material
  • allows easier diffusion of acid –> where demineralisation starts
17
Q

What is the histology of enamel caries?

A

Use of quinoline which shows up a number of zones:

  • translucent zone (deepest)
  • dark zone
  • body of lesion (corresponds to radiographic extent of lesion)
  • surface zone

Radiographs underestimate amount of caries

18
Q
A
19
Q

What is the transllucent zone?

A
  • 1st carious change
  • loss of ~1-2% mineral
  • few large pores due to loss of prism periphery
  • penetrated by quinoline (resin): appears traslucent ad quinoline fills large prism spaces
20
Q

What is the dark zone?

A
  • dark brown with quinoline
  • porosity 5-10%

Consists of: large and small pores

small: not penetrated by quinoline, therefore appear dark as they are filled by air or water
- demineralisation and remineralisation occurring

21
Q

What is the body of the lesion?

A
  • largest part and centre of the lesion
  • 25-50% porosity (half crystals are gone)
  • resin penetrates easily giving translucent appearance
  • corresponds to radiographic appearance
22
Q

What is the surface zone?

A
  • relatively intact
  • 30 microns thick
  • highly mineralised - high F content
  • porosity of ~1-2%: an area of redeposition of mineral dissolved from deeper layers, traps calcium phophate for environment of redeposition, oresence of fluoride promotes process of remineralisation
23
Q

What causes caries to arrest?

Why is fissure caries a problem?

A

If caries is not cavitated, it can arrest:

  • changes in environment: plaque control and fluoride, altered diet
  • can be brown: exogenous stains
  • histologically - wide, well-developed dark zone

Fissure caries results in 2 lesions, follows prisms, widening lesion, hitting ADJ and very hard to detect

M3: Oral Biology (5 decks)

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