Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BDS3 DMS > 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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the components of Decorative ceramic?

A
  • Kaolin 50+%
  • Quartz (silica) 15-25%
  • Feldspar 15-25%
  • Metal oxides <1%
  • Glass 0
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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%
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the two types of Feldspar?

A
  • Potash Feldspar (potassium alumina silicate)
  • Soda Feldspar (sodium alumina silicate)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are dental ceramics considered as ?

A
  • Glasses
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What property do metal oxides gives the ceramic?

A
  • Metallic oxide determine colour of ceramic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What colour does Chromium convey to ceramic?

A
  • Green
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What colour does Cobalt convey to ceramic?

A
  • Blue
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What colour does Copper convey to ceramic?

A
  • Green
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What colour does Iron convey to ceramic?

A
  • Brown
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What colour does Manganese convey to ceramic?

A
  • Lavender
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What colour does Nickel convey to Ceramic?

A
  • Brown
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is Leucite?

A
  • Potassium aluminium silicate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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%
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is meant by the term Coalesce?

A
  • Come together to form one mass or whole
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are some important properties required of conventional dental ceramics?

A
  • Aesthetics
  • Chemical Stability
  • Biocompatibility
  • Thermal Properties
  • Dimensional Stability
  • Mechanical Properties
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are the optical properties of dental ceramics?

A
  • Reflectance
  • Translucency
  • Opacity
  • Transparency
  • Opalescence
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is Static fatigue?

A
  • Decrease in strength even in absence of any applied load, it is time dependent
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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)
  • Tough

Strong 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

Zirconia
Lithium Disilicate (E-Max)
Precious metal
Non-precious metal
Titanium
Composite

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

BDS3 DMS (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions