4. Dental Porcelain Flashcards
DENTAL PORCELAIN
Defn: Porcelain
White transluscent ceramic that is fired to a ____ state.
Non ____ glasses ____ porcelain
glazed
crystalline
feldspathic
DENTAL CERAMICS
Solid materials composed of inorganic non-____ compounds
____, clay products, ____, glass etc.
metallic
pottery
glass
Classification of Dental Ceramics
• Today we are talking about PFMs
◦ You can have wrought alloys as you substrate for PFMs and crowns
• There are all ceramic crowns that include reinforced ____ and other veneering ceramic
• This is a general picture of ceramic crowns
ceramic
Advantages of Dental Ceramics Excellent \_\_\_\_ \_\_\_\_ appearance (esthetics) High resistance to \_\_\_\_ and distortion \_\_\_\_
• Ceramic have high biocompatibility
• They have great esthetics
◦ You can reproduce the natural color of teeth easily
• They have high resistance to wear and distortion, this makes them very durable
biocompatability
natural
wear
durability
Disadvantages of Dental Ceramics
____
Hard, difficult to ____ ____ opposing teeth
Does not bond to ____ base material (acrylic)
Produces ____ sound on contact
High ____
• Does not bond well to denture acrylic
◦ It is hard to use them as ____ teeth
brittleness polish wears denture clicking density denture
Dental Ceramic Restorations PFM porcelains Opaque Body \_\_\_\_ \_\_\_\_ (enamel) \_\_\_\_ \_\_\_\_
• Metal substrate under crown
• Right above the metal substrate is a layer of porcelain called ____ Porcelain
• Right above the Opaque Porcelain is ____ Porcelain
◦ There are different types of Body Porcelain to give a ____ look to the teeth
◦ There are several modifiers that help us produce ____ tooth color
• Why don’t we make the whole crown out of porcelain?
◦ Porcelain is not strong enough and will fracture ◦ ____ substrate is needed for support
dentin
incisal
translucent
modifier
opaque body natural natural metal
All- Ceramic crown
____ Strength Core
Aluminous ____ core CAD/CAM Ceramics
• Here we can see an all ceramic crown
◦ Notice I said “all ceramic” and not “all porcelain”
◦ We have a substrate that is high strength
‣ High strength ceramics are often ____ (Ex: zirconia, alumina)
• Over the high strength core ceramic we have ____ bonded to it, similar to how
porcelain is bonded to metal in a PFM
• More and more all ceramic crowns are being fabricated as CAD/CAM ceramics
• The whole crown can be made of one ____ instead of having other veneering
ceramics placed on them (Ex: all zirconia crowns)
high porcelain crystalline porcelain ceramic
Uses of Porcelain \_\_\_\_ teeth Jacket crowns \_\_\_\_ Porcelain-fused-to-metal crown and bridge work \_\_\_\_
• Jacket crowns are all ____ crowns
• Porcelain is a very translucent ceramic, therefore very easy to reproduce tooth
____
◦ Useful in making veneers
denture inlays veneers porcelain shades
General Composition of Porcelain
Feldspars 75-85% (Na2O.Al2O3.6SiO2/ K2O.Al2O3.6SiO2)
Alumina 0-10%
Quartz 12-22%
Kaolin 3-5%
(Al2O3-SiO2-H2O - clays)
Metallic oxides & pigments < 1%
• The main component of porcelain is ____
◦ Naturally available, it is a mined product
◦ There are 2 types, the first is ____ Feldspar (has sodium) ◦ The second type is ____ Feldspar (has potassium)
• Alumina and quartz are ____ materials that are added to improve ____ of porcelain
• Kaolin is a clay and makes the material ____
• Metallic oxides and pigments give us different ____
feldspar soda potash crystalline strength moldable shades
Composition of dental porcelains
• The point of this slide is to show that when we add sodium oxide and potassium oxide to our porcelain, we are reducing the ____
◦ As sodium oxide and potassium oxides increase, we have a lower ____
◦ We need this for porcelains that are fused to metals
firing temperature
fusion temperature
Structure of Porcelains
Structure of SiO2 glass and the
Effect of adding Na2O
• When we add sodium oxide or potassium oxide, we are opening up the ____ [bottom pic]
◦ Reducing firing temperature
◦ The added oxide also increases the ____ of the porcelain
structure
coefficient of thermal expansion
Role of Components
Feldspar
____
Oxides of ____,Sodium, and Calcium
____ formation
Quartz (SiO2)
Stability at high ____, strength
Alumina (Al2O3)
Increased ____ & viscosity
Kaolin (Al2O3-2SiO2..2H2O) ____, moldability
• Silica forms the ____
• The oxides break up the matrix, decrease the firing temp, and increase
the coefficient of thermal expansion
• Quartz and alumina provide strength and stability at high temperatures
• Kaolin is a clay material that provides ____
SiO2 potassium leucite temps strength binder matrix moldability
Classification of Dental Porcelains
Ultra low fusing < ____ F
• Which porcelain will you select for PFM crowns? ____ Fusing ◦ In order to process our porcelain, we stuck the porcelain on the
metal frame work and then it is heated
◦ We want a porcelain that fuses at a temperature that is lower than
the ____ of our alloy
1600
ultra low
melting point
Manufacture of Porcelain Powder Fritting
Heat mixture to form glass Leucite crystals
Quench to form a ____
Grind to desired particle size
Add ____ to form desired porcelain
Opaque, dentin, enamel & color modifiers
• Porcelain powder is made by mixing varying amounts of oxides in order to achieve different properties
◦ They are then heated to form a glass
‣ Leucite crystals can form during this process if there are not appropriate contr
• They can increase the ____ ◦ Mixture is then quenched (cooled suddenly)
‣ Pulverized into a powder call a frit
• The main metal oxide that is used to obtain different shades is ____
◦ Depending on how the iron oxide is fabricated, you can get many different shades
frit
metal oxides
coefficient of thermal expansion
iron oxide
Manufacture of Porcelain Powder
High fusing porcelains Feldspars melt and form \_\_\_\_ phase Final Microstructure 85% \_\_\_\_ phase 15% \_\_\_\_ quartz + alumina
Medium and low fusing porcelains
Fusion of glassy ____ powder particles
High content of ____ phase
• For high fusing porcelains, there will be an 85% vitreous phase with 15% quartz and alumina present
◦ These crystalline components ____ the porcelain
glassy vitreous crystalline frit vitreous strengthen
Microstructure of Dental Porcelain
This shows the micro structure of a crystalline material that is reinforcing the vitreous silicone dioxide phase.
When cracks propagate, they have to go through the high strength ____ faces. This is how they increase the strength of the porcelain
cystalline
Fabrication of porcelain restorations
Use of Glassy ____ powder particles
Little or no ____ reactions Reduced firing ____
more ____ composition than without fritting
• When making a PFM, want to use the powder that has been fabricated previously from the ____
◦ The components have already been heated, fused, and pulverized
◦ The reason is that when you do this initially, there will be a high amount of shrinkage
‣ So if it is pulverized already, we reduce the amount of ____ in the final restoration
◦ Also, when we are firing the porcelain on the metal, there are no ____ reactions taking place
frit pyrochemical shrinkage uniform frit shrinkage chemical
Characteristics of PFM Porcelains
Opaque Porcelains Addition of \_\_\_\_ oxides, TiO, SnO, ZrO, CeO \_\_\_\_ refractive index, Light scattering \_\_\_\_ particle size
____ metal surface
Masks ____ color
Initiates ____ development Thickness ____mm
insoluble high fine wets metal shade 0.1-0.5
Characteristics of PFM Porcelains
Body Porcelains
Dentin
Color of natural ____
____ range of shades
Enamel/Incisal
____
____ shade range
Translucent Porcelains Veneer over entire ____ Depth, enamel like translucency
dentin wide translucent restricted porcelain
Characteristics of PFM Porcelains Stains & Glazes High \_\_\_\_ oxide content colorant oxides \_\_\_\_ oxides High \_\_\_\_, Low fusing glass
Glaze
____ low fusing porcelain ____ appearance of enamel
Stain is designed to be very ____
◦ They will have high ____ and sodium oxide (reduce fusion temp of porcelain) ◦ Iron oxide is the main component giving us the shades we desire
◦ Because of the high alkali and oxide content, they have high fluidity and low fusing
temperatures
• Glazes are typically colorless and give a glossy appearance
◦ Good for ____ edge where teeth should be translucent
alkali
metallic
fluidity
colorless glassy fluid potassium inicisal
he Porcelain-Metal System System requirements
____ requirements ____ requirements Mechanisms of ____
metal
porcelain
bonding
Porcelain-Metal Restorations
Alloy requirements
High ____ temperature
High ____ resistance
Adherence controlling elements to form surface oxides: ____, Sn, ____
Coefficient of thermal expansion ____ (higher than porcelain)
reduce stress on porcelain
• The ally should have a high fusion temperature because the porcelain is heated on top of it ◦ Don’t want our porcelain fusing temp to get too close to ____ of alloy
• High sag resistance
◦ As you approach the melting temp of the alloy, it will begin to sag in the middle ◦ We want an alloy with a high resistance to this
• The adherence controlling elements form an oxide layer on the alloy that the porcelain can bond to
• We want a metal that has a slightly high coefficient of ____ than the porcelain ◦ Stress on the porcelain will be reduced when in function
fusion sag Fe In matching melting temp thermal expansion
Porcelain Requirements for PFM Low \_\_\_\_ ( High \_\_\_\_ metal content Na2O, K2O and CaO) Opaque with high \_\_\_\_ to mask metal Matched \_\_\_\_ Non \_\_\_\_
• Non greening
◦ Found in alloys that contain ____
◦ Green tint can be seen at ____
◦ This has been corrected in alloys used today
fusing alkali metallic oxides coefficient of thermal expansion greening silver margins
Porcelain Requirements for PFM
Thermal expansion
Coefficient of thermal expansion of metals change ____ from firing temp to room temp
Porcelain changes a lot ____
Alloy should ____ slightly
more than porcelain
put porcelain under ____
- The coefficient of thermal expansion of the metal and porcelain behave differently ◦ The job of the manufacturer is to match the porcelain to the alloy correctly
- The alloy should contract slightly more than the porcelain to put porcelain under compression and reduce tensile stresses on the porcelain
little
more
contract
compression
Porcelain Requirements for PFM
Repeated firings cause ____
Clouding
____ formation may also occur
change in coefficient of ____
• Potential problem, technician may make multiple additions to porcelain resulting in repeated firings
◦ This can cause devitrification
‣ ____ of porcelain
• Once crystals begin to form, porcelain gets ____
• Leucite can significantly change the coefficient of thermal expansion or porcelain
devitrification leucite thermal expansion crystallization cloudy
Stresses on PFM Crown
Loaded PFM crown
Metal under ____
Porcelain should be under ____
Stresses at metal porcelain junction
Design of PFM
- This is what we are talking about when we say we are putting porcelain under compression
- This ensures that the bond between the metal and porcelain is durable
- High stresses at the ____ can lead to crown failure [bottom pic]
tension
compression
junction
Mechanisms of Porcelain Bonding
____ forces
____ retention
• Van der Waals forces
◦ Weak bonding between the oxides of the ____ and the oxides of the ____
• Mechanical retention
◦ [top right pic] high magnification of the metal surface
‣ Very ____, powder particles will seep in resulting in increased retention
van der waals mechanical metal porcelain rough
Mechanisms of Porcelain Bonding
Chemical bonding
____
• One of the properties of the metal is adherence controlling elements (____, Sn, In)
◦ When gold or noble based alloys are heated, the oxides in the metal bond ____ to
the oxides in the porcelain (chemical compatibility)
• We can see here iron oxide and silicone dioxide in porcelain reacting to form chemical bonds
that help with bonding of porcelain to metal
iron oxide + silica
Fe
chemically
Mechanisms of Porcelain Bonding
Oxide layer on ____ bonds chemically to oxides of ____ porcelain
- Oxide layer on metal bonds to the opaque layer of the porcelain
- [right pic] shows the mechanical interlocking
- [bottom left pic] shows the chemical bonding
metal
opaque
Mechanisms of Porcelain Bonding
Chemical bonding
+____
____ quality
____ bonding
____ bonding
• This shows the contributions of the different mechanisms of bonding
• [left column] Experiment with a gold alloy not containing the adherence controlling elements
____, ____, and ____ (THIS IS THE 3rd or 4th TIME HE HAS REPEATED THESE!)
• Chemical bonding is increased with the adherence controlling elements
◦ The most important contribution to the bonding is ____ bonding
◦ Must follow the right techniques to obtain as much chemical bonding as possible
van der waals
oxide
compression
mechanical
iron
tin
indium
chemical
Compression Bonding
• When porcelain has been designed to be under compression [bottom], the compression force must be overcome before the ____ are seen on the surface of the porcelain
◦ This is the reason why we want porcelain under ____ (so it survives tensile stress)
tensile forces
compression
Bond Strength and Characterization
____ interlocking
____ bonding
Rely on mechanical ____
• You can take a PFM alloy and bond your opaque porcelain to it
• You can make a loading device like this that can determine how much force is needed to pull
the metal out
◦ Depending on whether the alloy contains adherence controlling elements or not, you can
determine how much of the bond strength is from having chemical oxides on the surface
mechanical
chemical
retention
PFM sequence
____ cleaning
____
• Here we have a 3 unit bridge, notice how the die was painted with a spacer
• [top right] we have our metal undercasting on the surface
◦ The surface is cleaned of all debris and then ground
• After it is ground, it is placed in oven for degassing
◦ Degassing - heating to create an ____ on the metal surface
• After degassing, ____ layer is stuck onto metal [bottom left]
◦ Place in oven and heat to prescribed temperature for firing
• Once opaque layer is fired, ____ layer is placed [bottom right]
metal surface degassing oxide opaque dentin
Application and Condensation of Porcelain
Methods
____ application gravitation
____
vibration
Condensation of powder particles
withdrawal of ____
surface tension packs powder
• You can mix the porcelain powder and distilled water and apply directly to metal surface a brush
◦ Other methods: gravitation, spatulation, vibration
• Once the powder/water solution has been applied, you must blot off moisture on surface
with ____
◦ This helps ____ the powder in place
brush spatulation water paper towel pack
Porcelain Powders
Powders have a range of particle sizes
40-49% porosity after ____ pressure compaction (wet vibration in mold)
30% porosity after ____ at 14.5 tones/in2
low
compaction
Firing and Microstructural Changes
Initial preheating
____ water removal to prevent void formation or fracture
Sintering
flow and fusion of adjacent particles
____ and change in pore shape
• Once the powder has been applied, you go through different stages of heating
• Place unit under heating chamber of oven and wait for a slow evaporation of the water
• After water has evaporated, you raise the unit into the heating chamber and it goes through
the ____ process
◦ Sintering - ____ of adjacent particles
◦ ____, change in pore shape (decrease in porosity)
slow shrinkage sintering fusion shrinkage
Sintering of Porcelain Important factors \_\_\_\_ surface tension \_\_\_\_
particle size
Ambient ____
(air vs. vacuum)
Biscuit stage
- This shows porcelain powder that has been sintered
- The particles are not exactly combined, but they are in close contact
- [reads important factors]
- After the ____ stage of firing, the surface feels crunchy and is described as the ____ stage of firing
temperature viscosity pressure first biscuit
Shrinkage & Porosity
Shrinkage during firing- 30%
Loss of ____ during drying
____
Porosity:
Air-fired porcelains - 7%
best ____ with large grain
Vacuum-fired porcelains <1% porosity
best translucency with ____ grain sizes
pores too small to interfere with light ____
• Shrinkage results from loss of water and the sintering process
◦ Because of this, technicians must ____ ceramic
‣ Takes a lot of practice
• Different porcelains are manufactured for air firing and vacuum firing
◦ You want to use a ____ grain porcelain powder for air firing
◦ In vacuum fired, the pores are too ____ to interfere with light transmission and do not
with esthetics
water
sintering
translucency
small
transmission
overbuild
large
small
Vacuum vs Air Fired Porcelains
Note differences in ____
porosity
PFM Sequence
- After the dentin porcelain is fired, this is what we get [top left]
- We then apply ____ and glazes for a natural appearance
stains
Porcelain Firing Cycles
Degassing ~ ____oC for 5 min
Porcelain Firing Firing temperatures Rate of temp \_\_\_\_ \_\_\_\_ time Cooling rates Restoration is placed under \_\_\_\_
- The first step after cleaning the casting is to heat it (____)
- [reads slide]
- Hold time - how long unit is held at a given temp
1000 rise hold thermocouple degassing
Glazing
Masks surface ____ in fired porcelain
provides smooth surface
minimize ____ debris retention and plaque formation
increases ____
Self-glazing
Controlled firing ____
Glaze powder with separate firing cycle
• After dentin porcelain, we apply a glaze
◦ [reads benefits of glazing]
• Self-glazing - Some dentin porcelains can be sent through a ____ firing cycle to produce a glaze
• Or you can apply a specific glaze porcelain to the surface with its own firing schedule
defects
food
strength
schedule
second
Types of Bond Failures
• This is important in diagnosing what went wrong
• If you can identify the type of failure, you can decide whether you want to fix it or
remake the crown
• If the failure is on the ____ surface there is nothing you can do and you must remake
a crown
• Failure between metal and porcelain = poor ____ formation on metal surface
• Failure within the porcelain can be fixed with ____
• Metal oxide-metal oxide - depending on the thickness of the oxide, you may be able
to bond ____ to it to restore
• Most times you must ____ crown because bonding techniques do not work often
metal
oxide
composite
composite
Bond failures
• [top right] complete exfoliation of porcelain from metal surface ◦ Failure happened within ____ on surface of metal
◦ We must ____ this crown
oxide
remake
Oxides on PFM alloys Noble Metals
A.
____
Pd-Cu
____
B.
____
Pd-Ag
• This shows that different alloys can give different quality of oxides on surface ◦ Copper containing alloys form a ____ oxide that is hard to mask
‣ undesirable in terms of oxide quality • Alloy on right is much easier to ____
Au-Pd-Ag
Pd-Ag
dark black
mask
Oxides on PFM alloys Base Metals
____
Ni-Cr
____
• Remember, we mentioned that Beryllium is added to base metal alloys because they improve the ____ of the metal, they also help to improve the quality of the ____ on the metal surface
◦ Easy to ____
◦ Easy to bind to ____
Ni-Cr-Be Co-Cr flow oxide mask porcelains
Improving Oxide Quality
Metal Deposition
Gold deposition followed by ____ to provide an
oxidized surface, also liven porcelain ____
Surface ____ for reducing oxide thickness on base metals
Improved bond strength and esthetics by limiting formation of ____ oxides
• Because of the poor looking oxide quality on some of the alloys, there are techniques (metal deposition) used to improve the surface
◦ Gold is applied, then tin
◦ Tin is oxidized on surface, gives lively porcelain color similar to what you would
get when bonding to a gold alloy
• Reducing oxide thickness on base metals
◦ Base metals, by nature of being a base, ____ easily and form thick oxides on the surface
‣ If oxide is too ____, bond will fail
• Bond strength and esthetics are improved by limiting oxides that are too ____ and too ____
tin color coatings dark oxidize thick dark thick
All- Ceramic Crowns
Ceramic core material High strength \_\_\_\_ porcelain \_\_\_\_ reinforced \_\_\_\_ infiltrated Alumina Cast \_\_\_\_ (Dicor) Crystalline ceramics \_\_\_\_
- In an all ceramic crown, instead of the metal (in a PFM), we have a high strength ____ material such as [reads list]
- We will learn more about all ceramic crowns in 3rd year
aluminous leucite glass glass zirconia ceramic
