Materials for Indirect Resotorations Flashcards
What should the choice of materials we choose allow for?
Allow for the realisation of patients cosmetic expectations but no require excessive preparation or involve the removal of a lot of sound tissue
Give some requirements the materials we use for indirect restorations should for fill
- Accuracy of fit
- Strength to resist occlusal forces
- Rigidity to avoid flexure and hence cement failure
- Should have a thermal expansion coefficient similar to the tooth
- Should not attract plaque
- Should be biocompatible
Give examples we can use to make crowns and bridges
- Metals
- Ceramic
- Metal ceramics (porcelain fused to metal)
- Indirect dental composite
Name the 2 types of metals we can use to make indirect restorations
- Gold and palladium alloys (precious metals)
2. Base metal alloys (non precious alloys)|
Give examples of some Gold and palladium alloys (precious metals) we can use to make indirect restorations
- Type III gold alloy
- Silver palladium
- Palladium-silver-gold
- Gold-silver-copper-palladium
- Palladium-copper
- Palladium-tin
Which type of gold alloy do we use for indirect restorations? What are the other types used for?
We use type III for indirect restorations
Type I and II are used for inlays
Give examples of some base metal alloys we can use to make indirect restorations
- Nickel-chromium
- Nickel-chromium-berylium
- Titanium
What factors do we take into consideration when choosing an indirect restoration material?
- Cost
- Corrosive resistance
- Strength
- Stiffness
- Hardness
- Ductility
If you ask for a gold crown to be made in the LDI what will you get
A material called 1 Star which is a medium gold casting allow
What is 1 star
A medium gold casting allow used to make gold crowns in the LDI
What is 1 star made from
- Gold (60.1%)
- Copper (18.9%)
- Silver (16.9%)
- Palladium (3%)
- Zinc (0.6%)
- Platinum (0.5%)
Describe 1 star
It is extra hard and yellow in colour
What is the role of gold in 1 star?
Gold adds to the:
1. colour
2. tarnish and corrosion resistance 3. malleability
of an alloy
Gold also increases the density of an alloy
What is the role of copper in an 1 star
Copper is a strengthener and enhances the colour of a silver-gold-copper crown and bridge alloy
What colour are copper rich silver-gold-copper alloys?
A reddish colour
What is the role of silver in 1 star
Silver is used in silver-gold-copper crowns and bridges to balance the reddening effect of copper
With copper it is used to control the strength and hardness of an indirect restoration alloy
What colour are silver rich silver-gold-copper alloys?
Greenish colour
Why can we not just use pure gold as an indirect restoration material?
It is too soft
What effect does reducing the gold content in a silver-gold-copper alloy have
Reducing gold content reduced density which may make casting more unreliable
What do silver and palladium do when they are molten? What problems can this cause?
They absorb oxygen when molten which can result in porous castings
What are some of the differences between base metal alloys and precious metals (in terms of being used as a restoration)?
- Base metal alloys have a higher modulus of elasticity so they are more rigid
- Base metal alloys are less flexible
What is a major drawback of base metal alloys
- You need very carefully control casting conditions
2. Increasing concern about the biocompatibility of dental alloys
Define material biocompatibility
The ability of a material to perform with an appropriate host response in a specific application
Give some issues surrounding biocompatibility of indirect restoration materials
- Grinding and casting fumes can result in conjunctivitis, dermatitis and bronchitis
- High levels of nickel are carcinogenic
- Nickel is well known to cause contact dermatitis
What is another name for porcelain fused to metal materials?
Metal ceramic alloys
Give examples of metal ceramic alloys
- High gold
- Gold palladium
- High palladium
- Silver-palladium
- Nickel-chromium
Do base metals or precious metals bond better to porcelain
Precious metals bond better
Name the metal ceramic alloy we use in the LDI
V delta SF
What is V delta SF made up of?
- Gold (51.5%)
- Palladium (38.4%)
- Indium (8.5%)
- Gallium (1.5%)
What is the role of indium in porcelain infused metal alloys
- Strengths and hardens both gold and palladium
- Increases the thermal expansion of gold and palladium
- Indium lowers the melting range of both gold and palladium
- Contributes to the formation of the bonding agent
What is the density of 1 star in comparison to v delta SF alloy
1 star: 13.6g/cm3
V delta SF alloy: 14.5g/cm3
What is the melting range of 1 star in comparison to v delta SF alloy
1 star: 840-875 degrees
V delta SF alloy: 1180-1300 degrees
How do porcelain based metal alloys work
Coping distributes stresses and provides rigid support (this inhibits propagation of cracks from small faults at the metal ceramic interface)
How is a good bond achieved between the metal and the porcelain in a metal ceramic allow?
- Mechanical retention (roughness)
- A direct chemical bond can be made using ion diffusion
- Mis match of the co efficient of thermal expansion can be used
What is the disadvantage of bonding metal to porcelain by using Mis matching of the co efficient of thermal expansion
The mismatch in coefficient of thermal expansion creates tangential compressive stresses in the ceramic.
What are some of the disadvantages of metal ceramic alloys
- Absence of light transmission especially in cervical and proximal areas
- Reduced depth of translucency
- Presence of fret line at gingival margin
- Some patients may have a sensitivity or be allergic to alloys
What can a nickel sensitivity result in?
Acute inflammation adjacent to the restoration
Why are we moving away from metal in the mouth and choosing ceramic based materials instead
Metals react very differently to natural teeth when exposed to light
Metals do not let light through where as ceramic crowns do
Out of all the different material we can use to make indirect restorations which is the most aesthetic?
All ceramic materials
List some different types of ceramic materials
- Conventional porcelain
- Glass ceramic
- Glass infiltrated alumina
- High tech ceramic
Which type of ceramic dental material has the highest toughness and bend strength? Which has the least?
Highest: High tech ceramic
Lowest: Conventional porcelain
What is a key disadvantage of ceramic dental materials
- They are quite brittle so they don’t bend they break
2. They are governed by flaws and can chip and fracture
State the Griffith equation
Failure stress= fracture toughness/ constant*(square root of critical flaw size)
How can we remove flaws from glass rods and ceramics
- Acid etch and lacquered
2. drawn silica fibres
What are ceramic materials regarded as
Flawed materials
What governs the properties of ceramic dental materials
Flaws disproportionally govern the properties or ceramic dental materials
Which is better ceramics or glasses?
Ceramic
What are ceramic materials usually made of?
Usually ceramic materials consists fo a crystalline material in a glass matrix.
why is ceramic better than glass
As if a crack forms in the glassy matrix of a ceramic material the crystalline domains deviate the crack hindering its progress and hopefully stopping it before complete failure
What is aluminous porcelain?
It is a high strength core porcelain containing unto 50% fused alumina crystals which a matched expansion veneer is baked
What does alum act as when it is added to porcelain
Acts as a crack stopper preventing cracks from propagating through the material thus increasing strength
Describe glass ceramic materials
They are fine grained polycrystalline materials which are obtained from an initially glassy phase following a heat treatment cycle
What are the benefits of glass ceramic materials
Thanks to the large number of fine crystals propagation of flaws through the glass ceramic can be limited
Which is better base glass or glass ceramic materials? WHY
Glass ceramic materials as they have far superior mechanical properties
Name a type of glass ceramic used in practice
IPS Emax
What are IPS Emac used fro?
Designed for crowns and bridgeworks
What is IPS Emax made up of
60% Lithium disilicate (main phase)
Lithium orthophosphate (secondary)
Layered with Fluoroapatite
Gives some indications for the use for glass ceramics
- Veneers
- Inlay
- Only
- Posterior, anterior crowns
- 3 unit anterior bridge
Talk though the CAD/CAM process
- CCD picture or video is processed
- A computer designs the restoration
- Computer mills the restoration ready to be used
Give examples of some core ceramics
- Alumina
2. Zirconia: Lava, Cercon, IPS eMAX
Give examples of zirconia materials
Lava,
Cercon,
IPS eMAX
What are the benefits of using zirconia
They are very strong and have good aesthetics
How is zirconia so strong?
It is made through a process of transformation toughening
What shape do we want the zirconia to be?
Tetragonal but when we reduce the temperature the zirconia wants to become monoclinic but we stop it from changing
What is the benefit of containing zirconia in a tetragonal shape
If a crack forms the constrains of the zirconia are released
- This means it changes its shape back to begin monoclinic
- Monoclinic zirconia occupies a greater volume in the bulk material
- This creates a compressive force that contacts the tensile forces causing the crack and therefore suppressing crack propagation
Name the 2 ceramic materials you are most likely to come across
- Lithium disilicate (glass ceramic)
2. Zirconium oxide core with a porcelain veneer
