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BDS3 Dental Material Science > Dental Ceramics > Flashcards

Dental Ceramics Flashcards

1
Q

Is all porcelain ceramic?

A

yes

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2
Q

Is all ceramic porcelain?

A

no

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3
Q

What is the key ingredient of decorative ceramics?

A

KAOLIN

-kaolin is a clay
-hydrated aluminium silicate
- opaque
- opacity is important for the appearance of the final product

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4
Q

How do dental ceramics become translucent?

A

kaolin is removed and feldspar and silica replace it

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5
Q

What are the components of dental ceramics?

A

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

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6
Q

make card from this

A
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7
Q

How are conventional dental ceramics supplied? and how is this component made

A

as powder

by heating the constituents to a high temperature >1000 degrees celcius

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8
Q

What are the stages of making conventional dental ceramics?

A
  • constituents heated to over 1000 degrees celcius
  • cool rapidly (fritting) - in water
  • mill the frit to a fine powder
  • add binder which is often starch
  • the powder is mixed with distilled water and built up into the restoration
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9
Q
A
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10
Q

How is a crown built up with conventional dental ceramic?

A

the crown is build up using different procelains for dentine and enamel (these are not tooth coloured)

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11
Q

How is the built up crown turned from a powder to a ceramic?

A

the crown is heated in a furnace to coalesce the power into ceramic

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12
Q

how much does the dental ceramic material contract during sintering?

A

about 20%

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13
Q

What does heating the powder and water ceramic mix lead to?

A

sintering

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14
Q

What is sintering and when does this occur with regards to creating a dental ceramic crown?

A

sintering is when the ceramic particles begin to fuse into a single mass

during sintering the glass phase softens and will coalesce

there is controlled diffusion over time and a ceramic mass is formed

(sintering occurs just after the glass transition phase)

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15
Q

What are the key properties of conventional dental ceramics? (6)

A
  • aesthetics
  • chemical stability
  • biocompatibility
  • thermal properties
  • dimensional stability
  • mechanical properties
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16
Q

Why are the aesthetics of dental ceramics so favourable?

A
  • colour stable
  • very smooth surface
  • retain their surface better than other materials -> less staining long term
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17
Q

What are 5 optical properties which favour the aesthetics of dental ceramics?

A
  • reflectance
  • translucency
  • opacity
  • transparency
  • opalescence
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18
Q

Why are dental ceramics seen as chemically stable?

A
  • generally unaffected by the wise pH range found in the mouth
  • dont stain
  • good biocompatibility - minimal adverse effects of biological tissues
19
Q

What are the thermal properties of dental ceramics?

A
  • similar to tooth substance
  • coefficient of thermal expansion is similar to dentine (low stressed to the restoration in the mouth during use)
  • thermal diffusivity is low
    protective of remaining tooth
20
Q

Is a ceramic crown a dimensionally stable material?

A

yes- once it is fully fired the material is very stable

HOWEVER during fabrication shrinkage is a problem and must be accommodated for by the technician

20% shrinkage is normal

21
Q

What are the mechanical properties of dental ceramics?

A
  • high compressive strength
  • high hardness (abrasion of opposing teeth if not glazed)
  • LOW tensile strength
  • LOW flexural strength
  • LOW fracture toughness

the last 3 can all lead to failure during loading

22
Q

What can occur during manufacture, finishing or occlussal wear of dental ceramics

A

surface micro -cracks

23
Q

Why can slow crack growth occur?

A

cyclic fatigue under occlusal forces in a wet environment over time

24
Q

What causes surface fatigue?

A

time dependant decrease in strength even in the absence of any applied load.

25
Q

What area should dental conventional feldspathic ceramics only be used in?

A

they can only be used in low stress areas

only anterior crowns

not in all patients (never if they have a bruxist habit)

26
Q

what core material was used to reinforce feldspathic core ceramics

A

alumina core

27
Q

What was the flex strength of alimuna core ceramics

A

> 120Mpa

28
Q

What were alumina core ceramics used as a core material for

A

porcelain jacket crowns (PJC’s)

29
Q

What was the purpose of alumina core prior to PJC’s?

A

to prevent cracks forming and causing the material to fracture

30
Q

What colour is aluminous porcelain

A

opaque

31
Q

Is an alumina core strong enough for posterior use?

A

no

32
Q

What is the maximum percentage of alumina in conventional aluminous cores?

A

50%

33
Q

what is the next stage after these core types to produce the final crown?

A

all of these core types are then veneered with conventional feldspathic porcelain to produce the final crown

34
Q

What were the problems with alumina cored crowns?

A

lack of flexural strength

good aesthetics but not suitable for anything other than single crowns

more successful anteriorly

35
Q

What has become the most popular ceramic core material?

A

zirconia crown - very hard

36
Q

What is the zirconia that is used in dentistry called?

A

Yttria-stabilised

37
Q

What temperature does zirconia power sinter?

A

1600 degrees celcius

38
Q

What enabled the use of zirconia as a core material?

A

CAD-CAM

39
Q

Can pure zirconia crack ?

A

yes - it can crack on cooling

40
Q

How much yttria is present in zirconia? and what happens if you increase the amount of yttria

A

3-5%

  • if you increase yttria the more translucency
  • if you inrease yttria this will reduce the physical properties
41
Q

what crystal structure is normal zirconia at room temperature?

A

monoclinic crystal

42
Q

what crystal structure is yttria stabilised zirconia at room temperature?

A

tetragonal crystal structure

43
Q
A

BDS3 Dental Material Science (3 decks)

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