All-Ceramics II Flashcards
The actual strength of a ceramic is always what
lower than its theoretical strength
What is the differences of the theoretical strength and the actual strength of ceramics
theoretical strength = 7000MPa
actual strength = 35-50MPa
What two things contribute to strengthening mechanisms of ceramics
fabrication defects
surface flaws
Who proposed that flaws act as a stress concentrator (magnifiers)
Griffiths
What does stress concentration apply
low locally applies stresses can result in very high effecting local stresses
What are two fabrication defects of ceramics
sintered powders introduce voids
casting and pressing result in potentially less flaws
What are two surface flaws of ceramics
grinding can introduce flaws (this is why polishing or re-glazing is critical)
usually failure occurs from the largest flaws
What are two aspects of chemical strengthening of ceramics
puts surface of ceramic in compression (pre-stress)
not commonly used in dentistry
What are two aspects in glazing of ceramics
self-glazing; tends to heal flaws
surface glazing can be designed to cool so they are under surface compression to improve strength
What are two characteristics of preventing stress corrosion of ceramics
ceramics are weaker when fracture occurs in water; water reacts with ceramics
ceramics fused to metal foil (captek) can reduce this
This is used to strength the ceramics
crystalline reinforcement
What is crystalline reinforcement
introduce increased crystal content in the glassy matrix to deflect cracks
What are two examples of glass ceramics crystalline reinforcement
glass ceramics; both silica based
leucite-reinforces (Empress)
lithium disillicate (eMax)
What is the strength of glass ceramics
moderate
What is the translucency of glass ceramics
good translucency
In which type of restorations can glass ceramics be used
full thickness restorations
In which three ways can glass ceramics be formed
pressing
machining
sintered powders
How is the shrinkage/fit of glass ceramics
no shrinkage/good fit
What is the strength of crystalline reinforced glass infiltrated alumina (InCeram)
high strength
What is the translucency of crystalline reinforced glass infiltrated alumina (InCeram)
poor
What is the shrinkage of crystalline reinforced glass infiltrated alumina (InCeram)
no shrinkage
What is crystalline reinforced glass infiltrated alumina (InCeram) used for
a core
How can you fabricate crystalline reinforced glass infiltrated alumina (InCeram)
it can be fabricated without special equipment
What is the strength of crystalline reinforced dense sintered alumina
high
What is the translucency of crystalline reinforced dense sintered alumina
low
What is crystalline reinforced dense sintered alumina used as
a core only
How can you fabricate crystalline reinforced dense sintered alumina
special equipment machine (CAD)
high temp ovens
What is the strength of stress-induced transformation dense sintered zirconia
high
What is the translucency of stress-induced transformation dense sintered zirconia
variable
What is stress-induced transformation dense sintered zirconia used as
a core or full thickness restoration
How can you fabricate stress-induced transformation dense sintered zirconia
special equipment machining (CAD)
high temp ovens
What steps happen when stress-induced transformation dense sintered zirconia undergoes stress
it leads to cracks
the lack of crystal constraint leads to crystals expanding (transformation)
resulting in reduced stress at crack tip
What are the four all ceramic systems available at OSU
Leucite reinforced glass-ceramic
lithium di-silicate glass-ceramic
full contour zirconia
porcelain fused to zirconia
What are two characterics of forming empress and eMax press
lost wax technique
hot-pressed
In which two ways an Empress and eMax be used
full contour with surface stain and glaze
minimal cutback with porcelain veneer
This type of fabrication technique is less labor intensive (less expensive), excellent outcomes, and has the full contour strength of material
surface staining
This fabrication technique is more labor intensive and expensive, excellent outcomes, full counter strength of material in high stress areas like the lingual or occlusal surfaces
minimal cutback with layered porcelain
This fabrication technique is the most labor intensive and expensive, has excellent outcomes, and the strength of material is reduced because thickness is reduced
full cutback with layered porcelain
How is zirconia supplies
isostatically pressed powders, stronger than chalk in this state but easy to mill
How much shrinkage does zirconia undergo
20%
What is the strength of zirconia
> 1000MPa
What is the crystalline structure of zirconia at room temperature
largest; monolinic
What is the crystalline structure of zirconia at 1170℃
intermediate; tetragonal
What is the crystalline structure of zirconia at 2370℃
smallest; cubic
Adding small amounts of this will cause the powders to stabilize in the tetragonal phase
yttrium (3%)
What is transformation toughening
crack causes local crystals to be unconstrained in some area
lack of crystal constraint allows phase transformation
phase transformation results in increase in crystal size
increase in crystal size closes crack
What are some unknowns of zirconia
it is still a ceramic and not a metal, so long term failure mechanism is still unknown for single crowns
What the low-temperature degradation of zirconia
because its metastable there is concern about transforming over time and creating flaws that lead to failures
How long has zirconia been used as a substructure and what has been found with fractures
10-15 years
minimal fracture
How long has zirconia been used for FCZ and what has been found with fractures
about 4 years
few reported issues
What are the steps to cement LDS and LRGC (leucite and lithium based)
etch ceramic with HF acid
apply silane
dual cure resin cement
apply adhesive to tooth
This step in cementation of LDS and LRGC preferentially removes glassy phase and leaves a rough surface
acid etch
This step in cementation of LDS and LRGC chemically bonds to hydrophilic glass surface to make the surface hydrophobic
silane
This step in cementation of LDS and LRGC bonds to silane surface and adhesive on tooth site
dual cure resin cement
What is the characteristic of zirconia cementation
zirconia is cemented similar to metal but the inner surface is not rough
Why not you etch zirconia to tooth structure
to keep the minerals in
