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Ceramics Flashcards

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1
Q

Examples of application of ceramics in dentistry

A
  • Indirect restorations
  • Crowns
  • Denture teeth
  • Inlays
  • Onlays
  • Veneers
  • Implant components
  • Fixed partial prostheses
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2
Q

Definition of a ceramic

A
  • Inorganic, non-metallic materials which are compounds formed between metallic elements and non-metallic elements
  • For example, silicon-oxygen in silicate glasses
  • Can be crystalline or non-crystalline (glassy or amorphous)
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3
Q

Bonding that occurs in ceramics

A

-Generally ionic and covalently bonded materials

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4
Q

Porcelain v Ceramic

A
  • Porcelain is a subset of ceramics
  • Porcelain is a ceramic but not all ceramics are porcelains
  • Porcelain refers to a specific composition of kaolin (hydrated aluminosilicate), quartz and feldspar (calcium, sodium and potassium aluminosilicates) exposed to high temperatures during formation
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5
Q

Types of ceramics used in dentistry and the common ones nowadays

A

-Silicate glasses
Entirely non-crystalline
Used as glazes only

-Porcelains
Predominantly non-crystalline
Used for veneers
Can also use glass ceramics

-Glass ceramics (mixture of crystalline and non-crystalline phases)
Used for inlays only as crowns and anterior bridges

-Highly crystalline materials (polycrystalline- used for crowns, bridges and implant materials)

Glass ceramics and highly crystalline materials most common nowadays

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6
Q

Properties of Dental Ceramics

A
  • Do not readily react with most liquids, gases, alkalis and weak acids
  • Remain stable over long periods of time
  • Can exhibit strength but their fracture toughness is much lower than metals
  • High hardness (can causes wear in opposing dentition)
  • Optically favourable for cosmetic applications
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7
Q

Why are ceramics getting increasingly used nowadays rather than all metal/metal ceramics

A
  • Aesthetics

- Cost and NHS (gold, palladium and platinum are very expensive)

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8
Q

Describe the structure of the glassy phase of dental ceramic

Components of structure and names

A
  • Glass= disordered structure
  • Network of silicon and oxygen is drawn in a fairly random way
  • Silicon oxygen (silicate) characterized by a tetrahedra (SiO4)
  • Silicone known as the network former
  • Alkali cations such as potassium or sodium can be added to disrupt the silicate chains to modify sintering temperatures or properties such as thermal expansion coefficient
  • Known as network modifiers
  • Atoms such as tituanium, aluminium, zirconium can act as an intermediate by both network forming and modifying actions
  • Both ionic and covalent bonds
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9
Q

Difference in structure and energy required between glassy and crystalline phases using silicon and oxygen as an example.

A

Disordered structure is glassy, amorphous state
Crystalline structure known as quartz is highly ordered with repeating unit cells

Greater energy is required to disrupt ordered systems- so increasing the crystallinity of a dental ceramic enhances the mechanical properties

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10
Q

What happens to a ceramic when you increase the crystallinity of it

A

-As you increase the crystallinity of a material,
You increase the energy required to disrupt the system
Increase the fracture toughness
Increase the strength
Increase the opacity
Increase the shrinkage after sintering

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11
Q

Explain the brittle nature of ceramics

A

-Theoretically ceramics real strength is massive

But

  • Inheritently weakened by any defects within it
  • The bigger the defect, the greater strength reduction

Brittle- when you load a material and it fails with very little deformation up to that point

  • Very little plastic deformation occurs at failure
  • Failure occurs rapidly
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12
Q

Clinical significance of fracture toughness of ceramics

A

-If a ceramic crown does not fit, so you use a bur to alter the shape or size, you are adding defects into the structure which greatly reduces its strength

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13
Q

Fracture Toughness definition and ceramics ft

A
  • Measure of the resistance to crack growth under a state of tensile stress
  • Ceramics have a low to moderate fracture toughness
  • Brittle material
  • Less time for cracks to propagate
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14
Q

Tensile Strength of ceramics

A
  • Theoretical tensile strength (amount of energy to pull atoms apart) of ceramics is extremely high
  • But ceramics are never defect free, and these defects determine the actual strength of the material
  • Strength varies with specimen size, shape, loading rate, surface prep and environment
  • Dental ceramics restorations fracture under tensile loading
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15
Q

Feldspathic Ceramics (Porcelain) definition

A
  • Mainly glassy with a minor crystalline component
  • Optically the best
  • Feldpar KAlSi3O8 is the main component
  • When feldspar melts it forms leucite and molten glass
  • Upon cooling, the separate structure of leucite and glass remains
  • Flexural strength of 60-80MPa
  • Closely matches shade translucency and luster of natural dentition
  • But low strength and prone to mechanical failure

-Addition of other crystal phases can increase the mechanical performance

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16
Q

How glassy ceramics are made and examples

A
  • Crystalline reinforcement of porcelains
  • Leading to mechanical toughening
  • Distribute higher strength crystals throughout the glassy matrix results in the crack having to go around the crystals in order to propagate
  • Crystal phase must have compatibility with the glass to be effective (If not, then the crystal will serve as a defect itself)

-Crystal phases used to reinforce the ceramic

  • Leucite Reinforced Ceramics
  • Lithium disilicates
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17
Q

Issue with increasing crystallinity in ceramics

A
  • Increase in shrinkage during sintering, which affects dimensional accuracy during fabrication
  • Decrease transparency
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18
Q

What properties of the crystal will determine the mechanical and optical properties

A
  • Crystal size, type and amount

- Important to match refractive index of the crystal and amorphous phase for translucency

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19
Q

Different manufacturing methods of ceramics

A
  • Sintering
  • Heat-pressing
  • Slip-casting (archaic so rarely used)
  • CADCAM
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20
Q

Sintered All-Ceramic Restorations explanation of procedure and common examples

A
  • Most aesthetic and oldest ceramics were sintered
  • Final object is formed by first pressing the constituents in powdered form under pressure into a mold, and then firing the pressed object at high temperatures
  • Often shaped on a die
  • Final ceramics are typically veneered in a translucent porcelain and glazed (heat treated) to improve aesthetic

-Examples of crystalline reinforced sintered dental ceramics include:
Alumina-based (up to 40% crystalllinity)
Leucite Reinforced Felspathic

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21
Q

Sintered Alumina-Based Materials properties, requirements and problems

A
  • Alumina is aluminium oxide, Al2O3
  • Added in 40-50% by weight
  • Excellent bond with the glass phase
  • Coefficient of thermal expansion between glass and alumina phases should be closely matched
  • Alumina ceramic is formed by dry-pressing and then sintering
  • Shrinkage of 10-20% can occur during sintering
  • Flexural strength of 600mPa

Shrinkage during sintering leads to dimensional inaccuracies
Opacity of the core requires veneering with glassy materials to improve aesthetics
Rarely used system nowadays
Competitor is leucite reinforced ceramics

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22
Q

Sintered Leucite-Reinforced Materials structure and properties

A
  • Potassium, aluminium, silicone and oxygen K(AlSi2O6)
  • Increased leucite content over traditional feldspathic porcelain which increases the flexural strength to over 100MPa
  • Leucite crystals have up to a 3-fold larger thermal coefficient of expansion compared to the glassy phase
  • During cooling, the leucite contracts more than the glass resulting in residual stresses. These resuldual stresses act as a crack deflecting mechanism and increase the strength

-Highly aesthetic- has been used extensively for anterior crowns and inlays

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23
Q

Heat pressing of all-ceramic restorations

A
  • Simultaneous application of both heat and pressure to form and sinter the ceramic
  • Employs a lost wax process
  • Contrast with sintering where constituent powders are first pressed and then fired
  • Pressures in range of 0.3-0.4mPa for 10-20 minutes
  • Temperature depends on the ceramics used
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24
Q

Why is heat pressing used over classical sintering. Examples of ceramics and how can you optimise properties

A
  • Improves crystal dispersion
  • Can obtain higher crystallinity
  • Decreases crystal size
  • Control dimensions of the material if it is pre-sintered as a lump and then heat pressed into a desired shape
  • Final heat-pressed ceramic is veneered with translucent porcelain
  • Leucite-Reinforced ceramics
  • Lithium disilicated-based ceramics
25
Q

Heat-Pressed All Ceramic Leucite-Reinforced Materials and advantages of sintered

A
  • Ceramics reinforced with K[AlSi2O6] in amounts between 35-55% by volume
  • In contrast with 45% achievable using sintering
  • 120MPa is the flexural strength
  • Increase over the strength of sintered leucite-reinforced ceramics
  • Reduced operator induced variability compared with sintered leucite ceramics
  • Improved strength as a result of increased crystallinity and improved dispersion
  • Similiar to sintered leuicte-reinforced, the coefficient of thermal expansion mismatch between crystal and glass phases creates a crack-deflecting mechanism
26
Q

Heat Pressed Lithium Disilicate Materials definition, uses and properties
Alternative name at Guys

A

-Can only be used anteriorly but not posteriorly
-Lithium disilicate, Li2Si2O5, is the major crystal phase up to 65% by volume
-Flexural strength 300-400MPa
-Similiar to leucite reinforced, crystal phase has a coefficient of thermal expansion mismatch with the glassy phase, creating a crack-deflection mechanism
-Crack deflection is further improved by the interlocking of elongated crystals
IPS e.max

27
Q

Slip-Cast All Ceramic Restorations examples

A
  • Interpenetrating phase composite
  • Ceramic frit layer is first condensed on a refractory die or a layer is machines from a preformed block
  • Glass phase is then drawn into the porous ceramic at high temperatures after the crystal phase has been sintered
  • Alumina-based
  • Spinel-based
  • Zirconia-toughened alumina
  • Much less common now
28
Q

CAD-CAM All-Ceramic Restorations definitions, classification disadvantage

A
  • Desired restoration (tooth or teeth) is scanned to obtain a digital recostruction (CAD)
  • Then imported to a milling device for machining of a bulk ceramic material (CAM)
  • Disadvantage can manifest through the use of machining with a brittle material
  • Bulk ceramic materials are either sintered or partially sintered in a block format, which are then machines to the final shape
  • Hard Machining: when ceramic is fully sintered before machining (either fully crystallized or partially crystallized)
  • Soft Machining: machining is performed on a partially sintered ceramic (Full sintering occurs after machining)
29
Q

Examples of fully sintered materials being used in CAD-CAM restorations and properties of these

Advantages of fully sintered

A

-Feldspar
Concentration on 30% by volume
Flexural strength of 120MPa

-Leucite-Reinforced
35-55% leucite by volume
Very similiar form to heat-pressed leucite-reinforced ceramics
120MPa flexural strength

-Lithium Disilicate
Can be machined either fully or partially crystallized
If partially crystallized, the structure contains both lithium metasilicate (Li2SiO3) and disilicate (Li2Si2O5)
Crystallization procedure post machining will depend on concentration of lithium disilicates
360MPa typical flexural strength

Hard-Machining CAD-CAM restoration production allows for rapid production of restorations in-clinic (hours) with more practical equipment as compared to other manufacturing methods

30
Q

CAD-CAM partially sintered materials examples and properties

A

-Alumina
High purity aluminium oxide used (99%)
Designed and manufactured in an oversized form to accommodate for shrinkage during sintering
Flexural strengths (500-650MPa)
Opaque to requires a veneering layer (feldspathic or glass ceramic)

-Zirconia
Tetragonal zirconia polycrystals are partially stabilized with yttrium
Highest flexural strength of all dental ceramics, randing from 900-1500MPa
Straying from perscribed surface/heat treatments of yttrium can alter structure and properites

31
Q

Mechanical toughening of Zirconia

A
  • Phase Transformation Reinforcement
  • Specific to ZrO2 ceramics (zirconia)
  • Tetragonal phase zirconia is only stable between 1170-2370 Degrees C
  • Yttria oxide (Y2O3) or cerium oxide can stabilize zirconia in its tetragonal form
  • When stabilized tetragonal phase zirconia reaches a threshold stress, it undergoes a transformation to monoclinic phase zirconia which includes a volume increase
  • The volume increase results in compressive stresses around the crystal, which stabilizes the crack
32
Q

Ceramic-Metal Restorations definition and structure of layers and process

A

-Restoration formed by at least 2 layers of ceramic on a metal framework

-Layer 1: Ceramic with opacifying oxides
Critical for bonding to the metal structure and aesthetically hiding the metal

-Additional Layers: Application of more translucent porcelain for size and colour matching

After additional layers are added, the restoration is vibrated and slowly dried to condense the ceramic

  • The restoration is then vibrated and slowly dried to condense the ceramic
  • Restoration is then sintered under vacuum at 0.1atm
33
Q

Importance of vacuum when sintering

A

-Decreases porosite of ceramic

34
Q

Requirements of materials involved in a

ceramic-metal restoration

A
  • Metal must have a melting temperature significantly greater than the firing temperature used for the ceramic. Metal cannot melt during application of the ceramic to metal core
  • Veneering porcelain should have a low temperature of fusion to eliminate distortion during sintering
  • Base porcelain must be able to wet the alloy adequately for proper ceramic-metal adhesion
  • Strong adhesion between the ceramic and metal- achieved primarily through oxides on the metal surface (chemical adhesion) and increased metal surface roughness (mechanical adhesion)
  • Coefficients of TE must be compatible. Metal typically designed to have a slightly higher coefficient of TE to place the ceramic in a state of compression upon cooling
  • High elastic modulus desirable to mitigate stresses and strains within the weaker porcelain
  • Metal shape should not change during the firing cycle of the cycle. Prolonged exposure of metals to heightened temperatures can cause changes in shape which can reduce the fit with ceramic
  • Design of shape is critical to reduce regions of stress concentrations
35
Q

Uses of Ceramics in indirect restorations and the possible ceramic options for each and INDICATIONS

A

-Porcelain Laminate Veneers
Dental porcelain or glass ceramics
Thin facings to correct colour, shape and position

-Ceramic Inlays and Onlays
Direct composite often used nowadays as less invasive
Onlays replacing cusps
Glass Ceramics or Dental porcelain

-Glass Ceramic crowns and bridges
Anterior crowns extending to pre molars
Anterior bridges
Glass ceramics (leucite or lithium disilicate)

-High strength core veneer crowns and bridges 
Anterior and posterior crowns 
Posterior bridges 3-unit 
Alumina Core or Zirconia Core 
with veneered dental porcelain

-Monolithic high strength crowns and bridges
All crowns
3-4 posterior bridges

-Porcelain fused to metal crowns and bridges
All crowns
Anterior and posterior bridges
Precious and non-precious alloys with dental porcelain

36
Q

Indications and classification of dental porcelains

A
  • Porcelain laminate veneers
  • Inlays
  • Onlays
  • Aesthetic veneering layer on high strength ceramic or metal cores
  • Fabrication of porcelain denture teeth

Classified according to the temperature they are sintered/fired at:

  • High fusing: 1300-1370 for denture teeth and aluminous core porcelain
  • Medium fusing: 1093-1260 for inlays and porcelain jacket crowns
  • Low fusing: as a veneering material for porcelain fused to metal crowns

The reason you want a low fusing porcelain is so you don’t damage the material that you’re veneering to

37
Q

Dental Porcelain Application steps

A

-Restorations are made using a compaction/condensation process:
1)Porcelain powder is mixed with water to form a paste
2) Paste is applied to a die (either a refractory material or platinum foil)
3) Fabricated from multiple powder to recreate the aesthetic features
4) Opaque powders are used to mask discoloured tooth cores
5) Dental shade are used to mimic the optical properties of dentine
6) More translucent enamel layers used to mimic enamel
7) As each layer is added the paste is condensed (vibrating and water removal)
Condensation aims to maximise particle density to minimise firing shrinkage
Optimisation of particle shape and size help the condensation process
8) At the end of condensation, the condensed powder is known as being a ‘Green State’

Then the porcelain is fired

38
Q

Firing of Porcelain Steps following compaction/condensation stage

A

1) Initially, heating is slow to drive off excess water (if you hear too quick, steam causes cracks)
2) Starch binder which may have been used is burnt out leaving no residue
3) Initial porcelain fusion occurs at point contacts between particles
4) Once the initial porcelain fusion has occured the object will hold its shape and is known as being in a ‘bisque state’

5) As temperature increases, more fusion takes place and molten glass flows drawing particles closer together and closing down voids to result in a non-porous material
6) Most shrinkage occurs at this stgae
7) Excessive heating leads to undesirable pyroplastic flow and the restoration will lose its form. Surface will also look highly glazed

8) Following sintering, slow cooling is required to minimise the generation of thermal residual stresses which may cause fracture
9) Vacuum furnaces are used during the whole firing process to reduce porosity
10) Porosity reduces strength and increases opacity

Porcelain is then glazed

39
Q

Glazing of porcelain steps after furnace and significance

A
  • Required to generate a smooth surface by filling in surface pores
  • Reduces biofilm formartion
  • Use glasses that fuse at low temperatures, either applies as a spray or liquid paint
  • Final firing of the crown under carefully controlled conditions allows for the glaze to adapt to the surface, fill any surface porosity without associated changes to the dimensions of the restorations
40
Q

Metal-ceramic restorations definition and failure

A
  • AKA porcelain fused to metal crowns
  • Overcomes the susceptibility of relatively weak ceramics failing due to fracture
  • Require application of a dental porcelain or glass ceramic to a metal core (known as coping)
  • Coping is made to closely adapt to the prepared tooth and the porcelain is applied to create a desired cosmetic outcome
  • Metal cropping covered by an opaque layer, covered by a gingival shade apically and a body of dentine coronally, and then a more translucent enamel shade superficially

Most likely failure is breakdown of the interface leading to chipping and delamination

41
Q

Strength of Metal-Ceramic Interface depend on

A
  • Mechanical retention (surface of the metal roughened using burs or airborne particle abrasion)
  • Chemical bonding during ceramic sintering (fusion between metal oxides at the metal surface and oxides in the ceramic) the bonding alloy must contain oxide forming elements for this to happen
  • Coefficient of thermal expansion of ceramic and the underlying material
42
Q

Importance of the correct coefficient of thermal expansion between the ceramic and metal and what happens with too big or too little differences

A
  • Correct coefficient of thermal expansion between the ceramic and a metal
  • Metal and porcelain chosen to have a slight mismatch is coefficient of thermal expansion
  • If mismatch is too great, then the ceramic will crack
  • If too little, then the ceramic will not be reinforced
  • Metal must have a higher coefficient of TE than the ceramic
  • On cooling after sintering, the metal cools at a quicker rate leading to generation of compressive stresses in the ceramic at the interface
  • If ceramic fails under tensile loading, the ceramic being placed in compressive stress means that a greater amount of energy is required for a crackt o propagate, thereby strengthening the ceramic itself
43
Q

Difference between precious and non-precious copings in MCCs and which do we not use more

A

-Precious: Rare, naturally occuring metallic elements that are often high of economic value
High palladium, high gold alloys

Nowadays we use non-precious

44
Q

Choosing the correct alloy for MCCs and different options

A

Melting temperature of the metal must be sufficiently higher than the sintering temperature of the chosen porcelain

1) High gold alloys for MCC restorations
Contains Pt or Pd to raise the melting temperature
Small fractions of oxide forming metals eg. Sn are added to increase chemical bonding potential to the ceramic
High cost of gold has reduced their usage considerably

2) Gold-Palladium alloys
Contain typically 50% gold with the balance Pd and Ag
Have similiar casting accuracy and common resistance to gold

3) Palladium-Silver alloys
Stiff (high elastic modulus)
Tendency to sag on porcelain firing 
30% silver with 60% palladium 
Ga, Zn, Cu and In as the balance 
More difficult to cast than gold containing alloys

4) Ni-Cr and Co-Cr
V stiff
Thin copings (prevents restorations from overcontouring)
Stiffness good for long span metal ceramic bridges
Very Difficult to cast
Made via CADCAM nowadays

45
Q

First high strength cores used, why they were invented and why are they no longer used

A
  • Increased fracture toughness and tensile strength and control excessive shrinkage associated with sintering compared to porcelains
  • Demonstrated that dispersion of high strength and elastic modulus alumina crystals within the glassy matrix of conventional feldpathic porcelain resulted in improved fracture toughness
  • But due to poor aesthetics and difficulties with varying shades associated with the increase in crystallinity, it was decided to add a layer of matched thermal expansion, low fusing feldspathic veneering porcelain to cover the cores appearance
  • Allowing for all ceramic posterior crowns
  • Major issue was matching the veneering ceramic with the core material to prevent chipping of the veneer
  • Initially maximum dispersion strengthening with alumina in the core was about 40%- beyond this there was excessive shrinkage on sintering and so the restoration had a poor fit
46
Q

2 types of modern high strength core-veneer restorations

Explanation of the procedure of the less commonly used one

A

-High purity alumina cores
Indicated for both anteriorly and posterior crowns
Die was digitized and then a new oversized die is created to avoid issues with shrinkage (predictive shrinkage)
Pure alumina is dry pressed to the oversized die
Sintered and shrinkage results in desired shape and size
Veneer with matched porcelain for aesthetics
Nowadays, pure alumina blocks are milled with CADCAM and then sintered
Provide strengths of around 600MPa, but less commonly used than zirconia

-Zirconia

47
Q

Zirconia restorations structural phases and properties of each phase

A
  • Zirconium oxide (Zirconia) is a crystalline material with 3 structural phases
  • Cubic, Tetragonal and Monoclinic
  • Strength of Zirconia is dependent on the dominant phase, which is dependent on the temperature

-Monoclinic (lower strength, occurpies a larger volume)
-Tetragonal (highest strength, reduction in volume)
-Cubic (moderate strength, lowest volume)
with increasing temperature

48
Q

Why do we have to modify Zirconia for use in dentistry and how do you do it

A
  • Zirconia in a fully crystallized form is too hard to machine effectively
  • Needs to be machined while partially sintered (green state) and then sinter it
  • During cooling from sintering a transformation occurs between the tetragonal structural phase to the monoclinic phase between 670 and 1070 degrees
  • Associated with an expansion of 3-4%, which would generate stresses which would crack the object
  • So you cannot use pure zirconia
  • Overcome by using a stabilising agent (Yttrium oxide)
  • Allows maintenance of the tetragonal form at oral temperature
  • Yttrium stabilised zirconia exhibits excellent properties- high strength and fracture toughness, high hardness and excellent chemical resistance
49
Q

How much should you stabilize ziroconia and effect of too much/too little

A
  • If you fully stabilise you end up in a cubic form, but you want a tetragonal form
  • Partial stabilisation with 2mol%to3mol% keeps it in a tetragonal form
50
Q

What properties of yttrium are important in formation of yttrium stabilsied zirconium

A

-Formation of structure is highly dependent on temperature, yttrium content and grain size (must be less than 0.8mm)

51
Q

Phase transitioning toughening of Y-TZP

A

-Zirconia is able to exhibit phase transformation toughening

  • Fracture toughness is the resistance of rapid crack propagation
  • Under stress such as crack propagation within the restoration, the tetragonal grains can be transformed to monoclinic
  • Associated with a 3-5% increase in volume, leading to compressive stresses generated which close the crack and prevent its extension
52
Q

Problems with Y-TZP in terms of structure and how do we overcome them

A
  • Properties are dependent on being able to maintain the tetragonal phase
  • Susceptible to an ageing process which diminishes fracture toughness and fracture resistance
  • Degradation of mechanical properties in presence of water
  • Slow surface transformation to a monoclinic stable phase
  • Begins at the surface and nucleates and cascades leading to micro cracks

Can reduce LTD by:

  • Reducing the particle size
  • Reducing the amount of stabilizing oxide
  • Excellent surface finishing reducing the initial defect population
  • Forming composite materials with alumina
53
Q

Problem with zirconia-core restorations and how is it overcome

A

-Chipping of the veneer layer due to:
mismatch in elasticity of core and veneer ceramics
Difficulties in effectively matching coefficients of TE
Limited chemical bonding (compared with bonding to metal oxides)
Poor framework design

Monolithic zirconia (made from a single zirconia substrate has been introduced)

54
Q

Monolithic zirconia explanation and how produced compared to normal zirconia

A
  • Single zirconia substrate
  • no veneering of porcelain

Reducing the % crystallinity and altering the grain size which leads to improved translucency at a cost of reduced toughness and strength)

Application of surface staining to add characterisation (incorporated into glazing)

55
Q

All the different types of indirect restorations used by ceramics and how they are cemented onto the tooth structure

A

-Porcelain Laminate Veneers
Adhesive Cementation
HF acid etch, silane coating and resin cementation

-Ceramic Inlays and Onlays
Adhesive cementation possible and provides better clinical outcomes
GIC cements

-Glass Ceramic crowns and bridges
Adhesive cementation possible and provides better clinical outcomes
GIC cements
Sometimes luting cements eg Zinc phosphate but clinical outcome poorer

-High strength core veneer crowns and bridges
Adhesive cementation challenging but there are methods
Alternatives are GIC cements and luting materials including zinc phosphate

-Monolithic high strength crowns and bridges
Adhesive cementation challenging but there are methods
Alternatives are GIC cements and luting materials including zinc phosphate

-Porcelain fused to metal crowns and bridges
GIC, RMGIC, zinc phosphate, zinc polycarboxylate cements

56
Q

Why is adhesive bonding to ceramics useful

A
  • Increases retention
  • For porcelain and glass ceramics it can increase the fracture resistance of a restoations
  • Often need to repair minor chips on veneering porcelain where the core is intact
57
Q

Bonding to porcelains and glass ceramics

A
  • Generate micro-roughness through acid (HF) etching which provides micro mechanical interlocking for the resin cement
  • SIlane coupling agent (3-MPS) links inorganic silica to the organic polymer of the resin-based material
  • Providing covalent bonding
58
Q

Bonding to zirconia

A
  • Bonding to zirconia and aluminate is challenging
  • Resistant to HF acid etching/no silica network for silane bonding

1) Microroughness produced using air abrasion or surface grinding
2) Chemical bonding either by using tribochemical coating (form of air abrasion using silica particles or silica coated alumina particles which through contact forced bond silica to the YTZP surface. Silane coupling agent is then used to bond to this layer

or

Following particle air abrasion use a phosphoric acidic monomer metal primer
Has a phosphate group which binds to aluminium oxides and zirconia oxides at one end and a methacryl group which co-polymerises with monomer from the resin cement

-Despite these strategies the bonding potential of zirconia and high purity alumina cores is considerably inferior to etched glass-ceramics

59
Q

Wear associated with dental ceramics

A

-Compared with other dental restorative- the wear resistance of all classes of dental ceramic used today is very high

-However due to the relative hardness of the ceramic compared with enamel and dentine, teeth opposing ceramic restorations can be subject to excessive wear
-This is worse if:
The glaze is lost over time
High hardness ceramics
Following adjustments to the surface leaving a roughened ceramic surface (occlusal adjustments must be highly polished following machining and ideally re-glazed if the crown has not been fitted)

Dental Material Science (13 decks)

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