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BDS3 DMS > 9 - Dental ceramics > Flashcards

9 - Dental ceramics Flashcards

1
Q

What is kaolin?

A
  • opaque clay
  • hydrated aluminium silicate
  • removed from dental ceramics to create translucency
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2
Q

What replaces kaolin in dental ceramics?

A
  • feldspar
  • silica
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3
Q

What are the constituents of dental ceramic?

A
  • kaolin <5%
  • silica 12-25%
  • feldspar 70-80%
  • metal oxides 1%
  • glass up to 15%
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4
Q

What is the function of feldspar in dental ceramic?

A
  • lowers fusion and softening temperature
  • flows during firing to form solid mass around other components
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5
Q

What colour does chromium convey to the ceramic?

A

Green

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6
Q

What colour does cobalt convey to the ceramic?

A

Blue

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7
Q

What colour does copper convey to the ceramic?

A

Green

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8
Q

What colour does iron convey to the ceramic?

A

Brown

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9
Q

What colour does manganese convey to the ceramic?

A

Lavender

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10
Q

What colour does nickel convey to the ceramic?

A

Brown

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11
Q

Describe conventional dental ceramics.

A
  • supplied as powder which melts together to form crown
  • crown is fabricated using different porcelains for dentine and enamel
  • made 20% too big due to contraction on firing
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12
Q

Define sintering.

A
  • when ceramic particles fuse to form a single mass
  • material will contract around 20%
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13
Q

Describe the aesthetic properties of dental ceramic.

A
  • colour stable
  • smooth surface
  • retain surface properties better than most materials and resist surface staining
  • have optical properties of reflectance, translucency, transparency, opacity and opalescence
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14
Q

Describe the chemical stability of dental ceramic.

A
  • chemical very stable
  • unaffected by wide range of pH in mouth
  • does not take up stain
  • good biocompatibility
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15
Q

Describe the thermal properties of dental ceramic.

A
  • similar to tooth substance
  • coefficient of thermal expansion is similar to dentine (low stresses to restoration during use)
  • thermal diffusivity is low which protects remaining tooth tissue
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16
Q

Describe the dimensional stability of dental ceramic.

A
  • once fired material is very stable
  • shrinkage during firing must be accommodated for by technician
17
Q

Describe the mechanical properties of dental ceramic.

A
  • high compressive strength
  • high hardness (can cause abrasion of opposing teeth )
  • low tensile and flexural strength
  • low fracture toughness
  • static fatigue can occur
18
Q

What is static fatigue?

A

Decrease in strength over time even in the absence of applied load

19
Q

Where can feldspathic ceramics be used in the mouth?

A
  • low stress areas
  • anterior crowns
20
Q

What are alumina cores used for?

A
  • used as core in porcelain jacket crowns (anterior)
  • act as crack stoppers preventing cracks from propagating
  • can only be used as core due to opacity
21
Q

How are alumina cores incorporated into crowns?

A
  • the cores are veneered to allow for conventional porcelain to be placed over top
  • only used in single crowns
  • more successful anteriorly
22
Q

What is incorporated into zirconia to stabilise it for dental use?

A

Yttria (3-5%)

23
Q

How does yttria improve the zirconia?

A

If a crack begins, the crystal structure will reach a critical level and transform to a monoclinic structure which expands and close up the crack

24
Q

How is a zirconia core fabricated?

A
  • impression of prep
  • model cast and scanned digitally
  • software created bridge substructure which minimum thickness connectors determined
  • raw zirconia milled
  • framework is heat treated and then stained
  • core is then veneered with feldspathic porcelain for final restoration
25
Q

What problems can arise with zirconia cored crowns?

A
  • expensive equipment initially
  • veneered porcelain could de-bond from core
  • core is opaque although better than metal
  • inert fitting surface cannot be etched or bonded
26
Q

What are the different types of milled cores for crowns?

A
  • zirconia
  • lithium disilicate
  • precious metal
  • non-precious metal
  • titanium
  • composite
27
Q

Describe the process of ceraming.

A

Two stages:
1 - crystal formation for maximum number of crystals
2 - crystal growth to maximise properties

28
Q

What should you use for posterior teeth?

A

Monolithic zirconia

29
Q

What should you use for anterior single crowns?

A

LiDiSi

30
Q

What should you use for anterior bridgework (short)?

A

LiDiSi

31
Q

What should you use for posterior teeth (long)?

A

Zirconia cored with zirconia where occlusal contacts meet

32
Q

What type of crown do you cement with conventional cement?

A
  • zirconia
  • LiDiSi
33
Q

What type of crown do you etch to create a retentive surface?

A
  • silica containing ceramic
  • can be bonded to using a silane coupling agent

BDS3 DMS (9 decks)

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