Ceramics and Zirconia Flashcards
What are the applications for ceramics?
-All-ceramic crowns, inlays, onlays, veneers, FPDs
-Metal-ceramic crowns and FPDs
-Implant abutments (and implants)
-Denture teeth
-Ceramic orthodontic bracket
What is the “best” part of ceramic?
HIGH esthetic capabiliies
What are the benefits of ceramics?
-Enhanced esthetics due to the absence of metal and improved light transmission
-Looks like a tooth!
-Most beneficial for teeth with normally colored dentin as the dentin color can affect restoration through the ceramic
- Physiologic gingival response when properly contoured and highly glazed/polished.
Why and How does ceramic look so much like a real tooth?
-Color Replication
—Ceramics can be tinted/colored to produce nearly any tooth shade
-Refraction
—Ceramics reflect and absorb light rays simulating enamel
- Translucency
—Type of porcelain (incisal/ dentin/ opaque)
What are the important properties of ceramics?
- flexural strength (brittle)
- fracture toughness (low; crack easy)
- ceramics shrink as they are fired
- ceramics are good thermal insulators
What is flexural strength?
-Defined as the strength of a material in bending
-Flexural strength is the point when stress on the outermost fibers of bending cause test specimen to fail
What does flexural movements do to ceramics?
cause them to fracture because they have low flexural strength
What is fracture toughness?
-Defined as the resistance to fracture when a crack is present
What is the fracture toughness of ceramics?
– have a low flexural strength (little plasticity). Ceramics do not deform easily so cracks propagate easily
What is the process of ceramics shrinking when fired?
sintering
What is the fracture toughness of metal?
- have a high FT due to plasticity at tip of crack, absorbs energy, making crack propagation more difficult
- Metals can deform without propagating the crack further
Why are ceramics a good thermal insulator?
–ceramics are poor conductors of heat
-Coefficient of thermal expansion (CTE) is low
- extremes of temperature can weaken and fracture ceramics
What do griffith flaws have to do with ceramics?
suggested that the low fracture strength of glass is due to the presence of microscopic flaws in the bulk material. Surface flaws act as stress initiators and cause widening and propagation of microcracks through the ceramic material
What is crack propagation?
Crack will propagate through material until a particle is met which stops the crack growth.
What is stress corrosion?
-Ceramic strength is reduced in moist environment
-Stress-dependent chemical reactions between water vapor and crack tip, causing crack growth and fracture with comparatively little occlusal loading
What is the sintering process?
-Ceramic powder/liquid is built up and molded (feldspathic porcelain)
-Process of heating ceramic powder once molded
-Called “Firing” the ceramic
-Sintering is the reduction of porosities between particles as the ceramic becomes more rubbery
What is lass transition temperature (Tg)?
-This is a range of temperature where porcelain starts to become molten
-A transition from solid to rubbery
-This is typically between 540 and 610 degrees Celcius
-This is below the ceramic melting point
(important)
What is heat pressing?
-Relies on external pressure to sinter and shape the ceramic at high temperature
-Restoration is made from a Wax pattern (lost wax technique)
-Also known as High Temperature Injection Molding
(often not as esthetic as traditional sintering)
What is the temperature range of glass transition temperature to make the ceramic rubbery?
540 and 610 degrees Celcius
(important)
What are the types of milling you can do with CAD/CAM?
- hard milling
- soft milling
What is hard milling with CAD/CAM?
-Already densely sintered material
-Silicate, glass ceramics, resin-based
ceramics
What is soft milling with CAD/CAM?
-Partially sintered material
—Zirconia and Lithium Disilicate (e.Max)
-Sintering to be completed in oven AFTER manufacture
What is used in the milling process to make it esthetic?
- multi-shade blocks (used to be limited)
- stain and glaze
What are the types of blocks used for milling CAD/CAM?
- glass ceramics (IPS Emax CAD)
- zirconia (IPS Emax ZirCAD)
- resin-ceramics
- resin
What type of material are veneers made of?
Predominately Glass
-Most translucent optical properties
-Weakest material
-Feldspathic porcelain
-Can ETCH this ceramic
What is the weakest type of porcelain?
Feldspathic porcelain
What type of material are e.Max made of?
Particle filled Glass Ceramic
-Less translucency
-increased strength
-Lithium Disilicate
-Can ETCH this ceramic
What type of material are zirconia made of?
Polycrystalline Ceramic
-Low translucency
-Highest strength
-Alumina, Zirconia
-Cannot ETCH this ceramic
What are the different methods used to strengthen ceramics?
- resin bonding
- reinforcement of the crystalline structure of the ceramic
- transformation toughening
What are the characteristics of resin bonding to ceramics?
-Can bond tooth to ceramic with the etchable ceramics
-Using a “coupling agent” called Silane enhances bond strength
-Resin cement either light cure or dual cure
What is important to know about reinforcment of the crystalline structure of a ceramic?
-Dispersed Crystalline phase – Higher strength and fracture resistance with crystals distributed through out the material
-Lithium Disilicate
What is transformation toughening?
-Stress induced phase transformation at crack tip
-Unique to zirconia
-Compressive forces at crack tip retard crack propagation
Transformation toughening is unique to what material?
zirconia
Resin bonding is a high strength cementation procedure, so bonding ceramics will ___________ the ability of the ceramic to flex.
decrease
Resin bonding with etchable glass ceramics leads to ___% increase in glass ceramic crown strength
50%
How the resin cements have so much strength?
- The movement of the cement into the dentin tubules forming microtags and into the porcelain spaces
- This forms a matrix that has great retention
How are veneers bonded to enamel?
resin bonding
What is important to know about veneers?
-Very thin “sheet” of porcelain as thin as 0.3 to 0.5 mm (minimal thickness)
-Tooth preparation is specific and is aimed at providing aesthetics and physical support for the veneer.
-Veneers are not under heavy occlusal loads.
-These are resin bonded to enamel
-Can be the most esthetic dental restoration possible
-Can be so thin, underlying tooth color can affect optical properties.
-By adding crystalline aspects to the
ceramic, crack propagation is much
more _________.
difficult
Small cracks begin, but then have a harder time causing catastrophic failure
What is the enamel flexural strength?
300 MPa
What is the flexural strength of feldspathic porcelain?
60-70 MPa
What is feldspathic porcelain used for?
veneers
PFM
What is the flexural strength of leucite reinforced ceramic (empress)?
120-160 MPa
Where can you use leucity reinforced ceramic (empress)?
anterior crowns
veneers
-Posterior Crown – No
-Onlay/Inlay – maybe (only where
occlusal force is low)
What is the flexural strength of lithium disilicate (e. Max)?
360-500 MPa
stronger than enamel (300 MPa)
What is lithium disilicate (e. Max) used for?
Veneers
Anterior and Posterior single crowns
Anterior bridges (particular cases)
Inlays/Onlays with low occlusal forces
Should you use e.Max for a posterior three unit bridge?
-Not Indicated
-Increased fracture of material
What is the survival rate of posterior three unit bridge for 5 years and 10 years made from e.Max?
5 years - 100%
10 years - 87.9%
What is the success rate of posterior three unit bridge for 5 years and 10 years made from e.Max?
5 years - 91.1%
10 years - 69.8%
What is the structure of zirconia?
polycrystalline structure
What are the features of polycrystalline structure?
-This provides increased strength
-This provides a surface that is not abrasive like porcelain, but instead is gentle on opposing dentition.
What is the wear resistance of zirconia?
low
- gentle on opposing teeth
Resin Bonding ________ increase the strength of Zirconia
will not
Zirconia needs the internal restoration surface to be…
roughened since it cannot be etched
How can you roughen the inside of a zirconia crown?
-roughen with Air abrasion or a diamond bur depending on generation of Zirconia you are using
What are the features of the original zirconia crown (bruxir)
- 3Y zirconia crown
- Horrible translucency aesthetic early on
- Poorly defined occlusal anatomt
- flexural strength around 1200 MPa
- any cement can be used
- crown has to be fired and will shrink about 25%
What is the flexural strength of the original zirconia crown (bruxir)?
1200 Mpa
How are zirconia crowns so strong?
-Transformational Toughening
—Stress induced transformation
—Unique to zirconia
—Compressive forces at crack tip retard crack propagation
_________________ with associated compressive stresses in vicinity of crack tip leading to crack closure in zirconia
Volume increase
How do they make zirconia more translucent?
-Adding more Yttria increases translucency
-This results in decreased strength
What is a way to make zirconia more esthetic without decreasing the stength as much?
To improve esthetics, a zirconia core is used and then porcelain is fused to create the tooth shape and color
What is a PFZ crown?
A PFZ crown is a porcelain fused to Zirconia
When do PFZ crowns fail?
Zirconia would not fail (very rare), it would be the porcelain that would fracture.
-Lack of porcelain support in zirconia substructure
-Proper occlusion is vital for PFZ success
-The bond between the Zirconia and the porcelain was not be able to overcome the difference in Coefficient of Thermal Expansion between the Zirconia core and the veneering porcelain
T/F: With some dark teeth, a zirconia core PFZ crown can be used to mask dark dentin
True
Is zirconia good on opposing teeth?
Yes!
Zirconia masks ______________ and is beginning to balance that masking with translucency
dark dentin
A monolithic zirconia 3Y crown preparation can be very conservative similar to…
gold or pfm crown preparations
If you want the most esthetic anterior restoration, what material would you choose?
- Veneer – Feldspathic Porcelain
- Crown – e.Max or Empress
If you want the most esthetic posterior restoration, what material would you choose?
-Crown – e.Max
-Crown - 5Y Zirconia
If you have a bruxing patient, what posterior restoration material would you use?
-Crown – 3Y Zirconia
-Crown – Gold
What crown material has the least amount of wear?
Gold and metal occlusal least amount of wear
How do you adjust occlusion on glass ceramic veneers?
-Only adjust after seated and bonded with resin cement
-Use fine diamonds with a little water
-Polish with diamond impregnated polishing paste
-Internal surface should not be adjusted if at all possible
How do you adjust occlusion on e.Max (lithium disilicate)?
-Adjustment outside the mouth is acceptable
-Fine diamond with a little water
-Polish with diamond impregnated polishing paste
-Internal surface should not be adjusted if at all possible
How do you adjust occlusion on zirconia?
-Adjustment outside the mouth is acceptable
-Fine diamond with a little water
-Polish with diamond impregnated polishing paste
-Internal surface needs either air abrasion or diamond bur roughing prior to cementing!
What is important about resin cements?
-Requires moisture free environment
-Required for low strength ceramics
-Requires silane coupling agent for etched ceramics
-Primer containing MDP placed on zirconia can enhance the chemical bond to cements containing resin
What is important about resin modified glass ionomer cements?
-Contraindicated in low strength ceramics
-Water absorption with setting of cement leading to slight expansion and possible fracture of ceramic at thin margin area
-Acceptable for Zirconia
