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REPOSITORY - Dental Materials Science > Dental Ceramics > Flashcards

Dental Ceramics Flashcards

1
Q

What is Kaolin?

A
  • Decorative ceramics contain Kaolin- It is a clay- Hydrated Aluminium silicate- Opaque- Opacity imp for appearance of final product
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2
Q

Why does Kaolin need to be removed from Dental ceramics?

A
  • Ceramics need to be translucent so Kaolin removed- Feldspar and silica replace it
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3
Q

What are the components of Decorative ceramic?

A
  • Kaolin 50+%- Quartz (silica) 15-25%- Feldspar 15-25%- Metal oxides <1%- Glass 0
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4
Q

What are the components of Dental ceramics?

A
  • Kaolin <5%- Quartz (silica) 12-25%- Feldspar 70-80%- Metal oxides 1%- Glass up to 15%
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5
Q

What are the two types of Feldspar?

A
  • Potash Feldspar (potassium alumina silicate)- Soda Feldspar (sodium alumina silicate)
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6
Q

What does Feldspar do in dental ceramics?

A
  • Acts as a flux- Lowers fusion and softening temp of glass- Has lowest fusing component and flows during firing forming a solid mass around other components
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7
Q

What are dental ceramics considered as ?

A
  • Glasses
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8
Q

What property do metal oxides gives the ceramic?

A
  • Metallic oxide determine colour of ceramic
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9
Q

What colour does Chromium convey to ceramic?

A
  • Green
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10
Q

What colour does Cobalt convey to ceramic?

A
  • Blue
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11
Q

What colour does Copper convey to ceramic?

A
  • Green
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12
Q

What colour does Iron convey to ceramic?

A
  • Brown
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13
Q

What colour does Manganese convey to ceramic?

A
  • Lavender
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14
Q

What colour does Nickel convey to Ceramic?

A
  • Brown
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15
Q

How are conventional dental ceramics used to build up into a restoration?

A
  • Supplied as a powder- Powder made by heating constituents to high temp >1000oC- Cool rapidly (Fritting) in water - This creates cracks and crazing of ceramic mass- Mill the fritt to fine powder- Add binder (usually starch)- Powder is mixed with distilled water and built up into restoration
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16
Q

What do feldspathic ceramics form when heated to 1150oC-1500oC?

A
  • Form leucites around glass phase of ceramic- Gives powder of known physical and thermal properties- No further chemical reaction needed during fabrication of restoration- Powder melts together to form the crown
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17
Q

What is Leucite?

A
  • Potassium aluminium silicate
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18
Q

How are conventional dental ceramics fabricated?

A
  • Ceramic powder mixed with water and applied to die with brush- Crown built up using different porcelains for dentine and enamel- They are not tooth coloured- Crown is heated in furnace to coalesce the powder into ceramic
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19
Q

What is Sintering?

A
  • Heating the crown leads to Sintering- When the ceramic particles begin to fuse into a single mass- Occurs just above glass transition temp
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20
Q

What happens during sintering of dental ceramic?

A
  • The glass softens and will coalesce- Over time controlled diffusion occurs and solid ceramic mass formed- The material contracts by about 20%
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21
Q

What is meant by the term Coalesce?

A
  • Come together to form one mass or whole
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22
Q

What are some important properties required of conventional dental ceramics?

A
  • Aesthetics- Chemical Stability- Biocompatibility- Thermal Properties- Dimensional Stability- Mechanical Properties
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23
Q

Why do ceramics have the best aesthetics properties of any dental restorative material?

A
  • Colour stable- Very smooth surface- Retain their surface better than other materials leads to less staining long term
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24
Q

What are the optical properties of dental ceramics?

A
  • Reflectance- Translucency- Opacity- Transparency- Opalescence
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25
Q

What is the chemical stability of dental ceramics?

A
  • Chemically very stable- Unaffected by wide pH range found in mouth- Do not take up stain from food/drink- Good Biocompatibility so minimal adverse effects on biological tissues
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26
Q

What are the thermal properties of Dental ceramics?

A
  • Sim to tooth substance- Coefficient of thermal expansion sim to dentine- Results in low stresses to restorations in mouth during use- Thermal diffusivity low which protects remaining tooth
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27
Q

What is the dimensional stability of dental ceramics?

A
  • Once fully fired material is very stable- During fabrication shrinkage occurs which is problem and must be accommodated by technician- Shrinkage of 20% during firing normal
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28
Q

What are the mechanical properties of conventional dental ceramics?

A
  • High compressive strength- High hardness (Can lead to abrasion of opposing teeth especially if not glazed)- Tensile strength – very low- Flexural strength – very low- Fracture toughness – very low (All lead to failure during loading)
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29
Q

What is Static fatigue?

A
  • Decrease in strength even in absence of any applied load, it is time dependent
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30
Q

Why is it thought Static fatigue occurs?

A
  • Due to hydrolysis of Si-O groups within material, over time in aqueous environment
31
Q

When can surface micro-cracks occur?

A
  • Occur during manufacture, finishing or due to occlusal wear- Fractures can initiate slow crack growth
32
Q

What is Slow crack growth?

A
  • Cyclic fatigue under occlusal forces in wet environment over time
33
Q

Why can conventional feldspathic ceramics only be used in low stress areas?

A
  • Due to static fatigue, surface micro cracks and slow crack growth
34
Q

What low stress areas can conventional feldspathic ceramics be used in?

A
  • Anterior crowns- Not in all patients- Too brittle elsewhere
35
Q

How can we overcome problems with conventional ceramics?

A
  • Aesthetics are good but need to be stronger- Produce strong coping, resistant to fracture - Cast or press a block of harder ceramic- Mill a laboratory prepared block of ceramic
36
Q

Why are alumina Cores used to reinforce feldspathic ceramics?

A
  • Core material- Flex strength double feldspathic porcelain >120Mpa- Alumina particles act as crack stoppers so prevent cracks propagating through material and causing fracture- Aluminous porcelain is opaque and can only be used as core material
37
Q

What are the benefits of alumina core?

A
  • Cheap to make- No specialist equipment needed, just furnace- Less labial reduction needed
38
Q

What are the negatives of Alumina core?

A
  • More palatal reduction required than metal crown- Not strong enough for posterior use - Enough room was needed for aluminous core and feldspathic layers above so aesthetics good but not amazing - Lack of flexural strength- Did not replace metal ceramic for bridgework or posterior crown
39
Q

What are some new techniques with increased alumina content?

A
  • INCERAM- PROCERA- Increases the strength
40
Q

What are alumina core veneered with to produce final crown?

A
  • Veneered with conventional feldspathic porcelain
41
Q

What are some newer techniques and materials other than Alumina?

A
  • Zirconia- Lithium Disilicate- Cores - Pressed crowns- Monolithic/Milled crowns- Advantages/Disadvantages of different types- Luting
42
Q

What is a Zirconia?

A
  • Most popular ceramic core- Zirconium dioxide naturally occurring material- Occurs in different forms at diff temp- Very hard- Used in jewellery industry
43
Q

What Zirconia is used in dentistry?

A
  • Yttria-stabilsed zirconia
44
Q

Why is pure zirconia not used in dentsitry?

A
  • Pure can crack on cooling- Zirconia powder does not sinter unless heated to over 1600oC
45
Q

What is the process of Yttria stabilisation of Zirconia?

A
  • 3-5% Yttria present in material - The more Yttria the more translucency but it reduces physical properties- Normal zirconia is monoclinic crystal at room temp- Yttria is a tetragonal crystal structure- If crack begins when stress at crack tip reaches critical level level the crystal structure transforms to monoclinic structure- Causes slight expansion of material and closes crack tip
46
Q

What properties does Yttria stabilisation give to Zirconia?

A
  • Hard- Strong (1000MPA flexural strength)- ToughStrong enough to use as bridge framework
47
Q

What is the process for fabrication of Zirconia Cone?

A
  • Impression taken of preparation snd sent to lab- Model is cast and scanned digitally- Software unit creates bridge substructure on virtual preparations- Minimum thickness of connectors determined and fabricated- Raw Zirconia block selected for milling- Presintered block easier to mill- Cut framework then heated to 850oC to achieve final properties- Framework stained appropriate colour- Then veneered with feldspathic porcelain to produce final restoration
48
Q

How long does milling take for three unit bridge?

A
  • Approx an hour
49
Q

What occurs during heating stage of Zirconia cone?

A
  • Causes 20% shrinkage- Computer software deals with this during milling process
50
Q

What are some Zirconia systems?

A
  • Zerion- Opalite- Everest ZH- LAVA from 3M first mainstream material
51
Q

What are some problems with Zirconia cored crowns?

A
  • Expensive equipment needed- Potential for veneering porcelain to debond from core- It is opaque so questions aesthetics- Inert fitting surface, can’t etch or bond
52
Q

What are some positives with Zirconia Cored crowns?

A
  • Once equipment is bough they are cheaper to make- As cost of metal is increasing- Fit is excellent
53
Q

What can be used to make Milled core crowns and bridges?

A

ZirconiaLithium Disilicate (E-Max)Precious metalNon-precious metalTitaniumComposite

54
Q

What do all ceramics have in common to get better aesthetics?

A
  • All have surface sintered layer
55
Q

What is the process of fabrication of a milled crown?

A
  • Cast goes into scanner- Scanned image of cast- Lower cast scanned and articulated - Select crown margin- Adjust crown margin- Select crown type and place on model for upper and lower- Adjust shape and size of selected crown on uppers- Save file and send to mill (GDH go to spain)- Requires final finishing (GDH do this on plaster model)
56
Q

How long does milling take for Milled crown?

A
  • 30-40 mins and crown is made- If return from Spain it is 48hrs
57
Q

Is the process the same for all materials used in milled crowns?

A
  • Yes- Zirconia- LiDiSi- Metal- Ceramic filled composite resin
58
Q

What is the method of fabrication of a Milled crown if you have fully digital workflow?

A
  • Don’t need models and impressions- Scan in mouth- Design on CAD machine- Mill - Polish- Cement
59
Q

What is the method for cast and pressed ceramics and what is it called?

A
  • Restoration waxed up as you would metal restoration- Invested- Cast from heated ingot of ceramic 1100oC- Once devested and cleaned the restoration heated- Called Ceraming
60
Q

Why does sintering not occur in Ceraming?

A
  • Ceramic ingot already fully condensed prior to filling
61
Q

Why is the ceramic ingot heated in Ceraming?

A
  • Heated to improve crystal structure producing crack inhibiting crystals
62
Q

Why are cast crowns veneered?

A
  • Can be stained- Most often cut back labially and veneered with appropriate felspathic porcelains
63
Q

What ceramics are used in cast and pressed ceramics?

A
  • Called glass ceramics- Lithium Disilicate Glass- Leucite Reinforced Glass
64
Q

What are the two stages of Ceraming?

A
  • Stage 1 crystal formation maximum number of crystal nuclei are formed- Stage 2 crystal growth to maximise the physical properties- Crystal phase of the ceramic can approach 100%
65
Q

Why are lithium disilicate glasses used in cast and pressed ceramics?

A
  • Strong material which has small crystal size and high vol fraction of crystals- Have unique needle-like crystals- Makes crack propagation very difficult = good fracture toughness- Good flexural strength 350MPa
66
Q

What are some advantages of different crowns?

A
  • Monolithic block crowns, milled from a single block of material are strongest- Zirconia based crowns are stronger than LiDiSi- LiDiSi have better translucency hence better aesthetics- Crowns with layered porcelain rather than just stained monolithic block have better aesthetics- Layered crowns are more likely to chip due to stresses between core and
67
Q

What process creates a stronger crown - Sintered or Milled?

A
  • Milled crown of same material gives stronger crown- Block is subjected to ideal heat treatments to maximise properties- Blocks will be consistent- As aesthetics of these blocks improve they will become most commonly used crown for all mouth not just posterior
68
Q

What material should you choose for posterior teeth?

A
  • Monolithic Zirconia- Can be used for single crowns and shorter span bridges
69
Q

What material should you choose for anterior teeth single crowns where aesthetics most important factor?

A
  • LiDiSi- Can probably use as far back as first premolar
70
Q

What material should you choose for anterior bridgework?

A
  • Short span with no parafunction use LiDiSi- Longer span or heavier occlusion use Zirconia cored with zirconia where occlusal contacts meet
71
Q

What can Zirconia and LiDiSi crowns be cemented onto tooth with?

A
  • Can use conventional or resin cements- Don’t require to be bonded to tooth substance to prevent fracture as they have own intrinsic strength
72
Q

What can Silica containing crowns be cemented to tooth with?

A
  • can be etched ,with hydrofluoric acid to produce retentive surface - etched surface can be bonded using silane coupling agent, to tooth using appropriate bonding agent and resin cement
73
Q

What are Zirconia cored crowns not affected by?

A
  • don’t contain silica and not affected by acid - can be abraded by air to create retentive surface but are strong enough to be self supporting
74
Q

What is the definition of Translucency?

A
  • Ratio of intensity of transmitted light to that of incident light

REPOSITORY - Dental Materials Science (19 decks)

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