Brainscape's Knowledge GenomeTM

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


See full index

bds3 dental materials > dental ceramics > Flashcards

dental ceramics Flashcards

1
Q

porcelain

A

all porcelain is ceramic, but not all ceramic is porcelain

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

kaolin in decorative

A

Kaolin is a clay
Hydrated Aluminium Silicate
Opaque
Opacity is important for the appearance of the final product
Dental Ceramics need to be translucent so Kaolin is removed and feldspar and silica replace it

so glass is up to 15%

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

dental ceramics are glasses

A

Feldspar
Potash feldspar (potassium alumina silicate)
Soda feldspar (sodium alumina silicate)
Acts as a flux
Lowers the fusion and softening temperature of the glass
It is the lowest fusing component and flows during firing forming a solid mass around the other components

Borax
Silica
Metallic Oxides

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

metal oxides convey colour

A

Chromium GREEN

Cobalt BLUE

Copper GREEN

Iron BROWN

Manganese LAVENDER

Nickel BROWN

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

conventional dental ceramics

A

Conventional dental ceramics are supplied as powder
The powder is made by heating the constituents to a high temperature >1000oC
Cool rapidly (Fritting)
In water creating cracks and crazing of the ceramic mass
Mill the Frit to a fine powder
Add binder
Often starch
The powder is mixed with distilled water and built up into the restoration

Feldspathic ceramics form leucite when heated to 1150-1500oC
Leucite is potassium aluminium silicate
This forms around the glass phase of the ceramic.
Gives a powder of known physical and thermal properties.
No further chemical reaction is required during fabrication of the restoration
The powder melts together to form the crown

ceramic powder is blue or pink

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

fabrication of the crown

A

Ceramic powder is mixed with water and applied to the die with a brush
The crown is built up using different porcelains for dentine and enamel
These are not tooth coloured
The crown is heated in a furnace to coalesce the powder into ceramic

pink dentine, blue layered on top

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

sintering

A

powder comes together and solidifies, 25% reduction in size

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

properties 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
9
Q

aesthetics

A

Ceramics have the best aesthetic properties of any dental restorative material
Colour Stable
Very smooth surface
Retain their surface better than other materials -> less staining long term

Optical properties
Reflectance
Translucency
Opacity
Transparency
Opalescence

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

chemical stability

A

Chemically very stable
Generally unaffected by the wide pH range found in the mouth
Do not take up stain from food/drink
Good BIOCOMPATIBILITY minimal adverse effects on biological tissues

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

thermal properties

A

Similar to tooth substance
Coefficient of thermal expansion is similar to dentine

Results in low stresses to the restoration in the mouth during use

Thermal diffusivity is low
Protective of the remaining tooth.

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

dimensional stability

A

Once fully fired the material is very stable
During fabrication shrinkage is a problem and must be accommodated for by the technician
Shrinkage of 20% during firing is normal for a conventional feldspathic ceramic crown

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

mechanical properties

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

Static Fatigue
Time dependant decrease in strength even in the absence of any applied load. Probably due to hydrolysis of Si-O groups within the material, over time in an aqueous environment.

Surface micro-cracks
Can occur during manufacture, finishing or due to occlusal wear. These are areas where fractures can initiate
Slow crack growth
Cyclic fatigue under occlusal forces in a wet environment over time

All of these problems mean that conventional feldspathic ceramics can only be used in low stress areas.
Only anterior crowns.
Not in all patients
Too brittle for use elsewhere

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

overcoming the problems with conventional ceramics

A

Aesthetics are good but they need to be stronger

Produce a strong coping, resistant to fracture, and cover in conventional porcelain

Cast or press a block of harder ceramic

Mill a laboratory prepared block of ceramic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

strong coping

A

metal coping
alumina core
zirconia core

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

allumina core

A

Alumina reinforced feldspathic core ceramics since 1960s
Used as core material in PJCs
Flex strength double that of feldspathic porcelain >120Mpa
Alumina particles act as crack stoppers preventing cracks propagating through the material and causing fracture
Aluminous porcelain is opaque and can only be used as a core material

This type of core was used as the first choice crown for anterior teeth for decades
It is not strong enough for posterior use
Aesthetics could be excellent but enough room was required for aluminous core and feldspathic layers above.
Possibly more palatal reduction required than in a metal ceramic crown, but less labial reduction required.
Relatively cheap to make
No specialist equipment required, just a furnace.
Conventional Aluminous cores are a maximum of 50% alumina
Increased alumina content increases the strength  new techniques
INCERAM
PROCERA
Both complicated fabrication techniques
First used in the 1990s

17
Q

allumina cores

A

core types are veneered with conventional feldspathic porcelain

Problems with all alumina cored crowns remains lack of flexural strength
Aesthetics are excellent but probably not suitable for anything other than single crowns
Much more successful anteriorly
Did not replace metal ceramic for bridgework or posterior crowns

18
Q

newer techniques and materials

A

Zirconia
Lithium Disilicate
Cores
Pressed crowns
Monolithic/Milled crowns
Advantages/Disadvantages of different types
Luting

19
Q

zirconia core

A

most popular ceramic core material.
Zirconia (Zirconium Dioxide) is a naturally occurring mineral
It occurs in different forms at different temperatures
Very hard
Used extensively in Jewellery industry as imitation diamonds

Until CAD-CAM was introduced the use of Zirconia as a core material would not have been possible
Zirconia powder does not sinter unless heated to over 1600oC
The Zirconia used in dentistry is Yttria-stabilised zirconia
Pure zirconia can crack on cooling

20
Q

yttrium stabilisation

A

SMALL CRYSTAL TO BIG CRYSTAL

Very small amounts of Yttria is present in the material
3 – 5%
The more Yttria the more translucency
More Yttria reduces the physical properties
Normal Zirconia is a monoclinic crystal at room temperature
Yttria  a tetragonal crystal structure
If a crack begins when the stress at the crack tip reaches a critical level the crystal structure transforms to the monoclinic structure
This causes a slight expansion of the material and closes up the crack tip
This ability  a material which is very
Hard
Strong (1000MPA flexural strength)
Tough

Strong enough to use as a Bridge Framework

21
Q

fabrication of a zirconia core

A

Impression is taken of the preparation and sent to the lab
A model is cast and then scanned digitally
Software Unit Creates a bridge substructure on virtual preparations
Minimum thicknesses of connectors are determined and fabricated
Raw Zirconia block is selected for milling
A presintered block is much easier to mill
Milling for a three unit bridge will take around an hour
The cut framework is then heat treated at around 850oC to achieve its final physical properties
This causes a 20% shrinkage but the computer softwear deals with this during the milling process.
The framework is also stained to an appropriate colour
Some modern zirconias are available in different shades
The Zirconia core is then veneered with feldspathic porcelain to produce the final restoration

22
Q

problems with zirconia cored crowns

A

Expensive equipment required
Potential for veneering porcelain to debond from core
Zirconia core is opaque ? Are aesthetics much better than metal ceramic
Inert fitting surface, cannot etch or bond

BUT
Once you have the equipment, they are cheaper to make
Cost of metal is increasing
Fit is generally excellent

23
Q

milled core crowns and bridges

A

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

ceramics all have a surface sintered layer for best aesthetics

24
Q

fabrication of a milled crown

A

cast goes into a scanner
same methods irrespective of material being used
scanned image of cast
lower cast is scanned is articulated
select crown margin
adjust crown margin
select crown type and place on ‘model’
adjust shape and size of selected crown

25
Q

fabrication of milled crown

A

Save file
Send to milling machine
Can be anywhere in the world
GDH mainly go to Spain
30 – 40 minutes you have your crown
In GDH return from Spain takes 48hrs
Still requires final finishing
In GDH this is still done on a plaster model

If you have a truly digital workflow you can dispense with models and impressions.
Scan in the mouth
Design on CAD machine
Mill
Polish
Cement

26
Q

cast and pressed ceramics

A

A different technique more like casting a metal restoration
The restoration is waxed-up, as you would for a metal restoration
Invested
Cast from a heated ingot of ceramic (1100oC)
No sintering occurs the ceramic ingot is already fully condensed prior to firing.
Once devested and cleaned the restoration is heated to improve its crystal structure producing crack inhibiting crystals.
This process is called CERAMING

The cast crown can be stained
More often it is cut back labially and veneered with appropriate feldspathic porcelains

27
Q

glass-ceramics

A

The ceramic used in these processes are called glass-ceramics.
Lithium Disilicate Glass
Leucite Reinforced Glass

CERAMING
Two stage process
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%

Strong materials have small crystal size and high volume fraction of crystals
Lithium disilicate glasses have a unique needle-like crystals
This makes crack propagation through this material very difficult  Good Fracture toughness
good flexural strength 350MPa

28
Q

advantages of different crown types

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

29
Q

sintered vs milled

A

For the same material a milled crown will be stronger than a built up or pressed crown.
The block will have been subjected to the ideal heat treatments to maximise its properties and all blocks will be consistent
As aesthetics of ‘blocks’ of ceramic improve these will become the most commonly used crown.
Already acceptable in posterior teeth.

30
Q

how to decide what to use?

A

Posterior teeth
Monolithic Zirconia
Can be used for single crowns and shorter span bridges
Anterior teeth single crowns where aesthetics are the most important factor
LiDiSi
Can probably use as far back as first premolar
Anterior bridgework
Short span with no parafunction
LiDiSi
Longer span or heavier occlusion
Zirconia cored with zirconia where occlusal contacts will meet

31
Q

luting crowns

A

Both Zirconia and LiDiSi crowns can be cemented with conventional or resin cements.
Both kinds of crowns have intrinsic strength and do not rely upon being bonded to tooth substance to prevent fracture
Neither ceramic crown performs better than a metal crown luted with a conventional dental cement over time
Conventionally cemented metal restorations revealed significantly lower failure rates compared to adhesively-luted ceramic ones. (C Tennert et al. Dental materials 38 (2022) 1623–1632)
Any silica containing ceramic can be etched with hydrofluoric acid to produce a retentive surface (LiDSi crowns)
This etched surface can be bonded to, using a silane coupling agent and in turn bonded to the tooth using an appropriate bonding agent and resin cement
Zirconia cored crowns do not contain silica and are not affected by acid but can be air abraded to create retentive surface
They are strong enough to be self supporting and can be luted with a conventional dental cement.
Some evidence of bonding to 10-MDP containing bonding agents if resin cement is to be used

bds3 dental materials (9 decks)

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