Dental Materials: Zirconia Flashcards
Benefits of Zirconia crowns
- comes in multiple strengths and translucencies
- durable
- one appointment visit
- less tooth prep
- can be layered with procelain for more tooth like aesthetics
- crown can be cemented or bonded
- biocompatible (no adverse reactions)
- for patients that grind their teeth
What is the metal of zirconia?
zirconium
How strong is zirconium?
Similar to titanium
How is cubic zirconium formed?
When white zirconium dioxide is heated to very high temperaturesW
What is another word for tetragonal zirconium?
Zirconium dioxide
Cubic zirconium is ____________ in nature, but can be synthesized to a very hard, optically flawless, and colorless gemstone.
rare
What are the 3 phases of zirconia?
- monoclinic
- tetragonal
- cubic
What is cubic zirconia?
cubic crystalline form of ZrO2
- has optical properties like diamond
What is dental zirconia?
modified yttria tetragonal zirconia polycrystal
Why is yttria added?
Stabilize the crystal structure transformation during firing at an elevated temperature
What is the tetragonal phase for?
toughness (strength)
What is the cubic phase for?
translucency (esthetics)
Which phase of zirconia is not useable for dentistry?
Monoclinic
What is the amount of yttria in tetragonal zirconia?
3% yttria
high strength zirconia
What is the amount of yttria in cubic zirconia?
> 5% yttria
“esthetic” high translucency zirconia
What does yttria content determine?
strength and translucency by adjusting phase composition
Yttria ________ tetragonal polycrystals.
Stabilized
As yttria percentage increases, the ___________ increases, but the _____________ decreases.
- translucency
- strength
Which is the most opaque zirconia?
3% yttria zirconia
mainly tetragonal zirconia
Which is the most translucent zirconia?
5% yttria zirconia
more cubic/ess tetragonal phase
What percentage yttria results from tetragonal and cubic phases?
4%
How does the tetragonal phase function to improve strength?
When faced with force, instead of shattering, turns into monoclinic crystal (harder)
hinder crack propagation
What is transformation toughening?
When tetragonal particles that normally constitutes Zirconia transform into a stronger monoclinic particle in response to cracks, so the crack does not propagate
Do all zirconia generations have the transformation toughening property?
No
cubic zirconia does not have this ability
Why does 3% yttria have low transparency?
scatter/refract at smaller tetragonal crystal boundaries
Why does 5% yttria have high transparency?
reducing light scattering and deflection
larger cubic crystals with isotropic optical properties
Where is 3Y best in the dental anatomy?
Posterior teeth
due to low transparency and esthetics
Where is 5Y best in the dental arch?
Anterior teeth
due to high transparency and esthetic
Monolithic zirconia vs. Bilithic Zirconia
Monolithic = one layer (stronger) = 3Y
Bilithic = layers of different ceramic powders (more translucent) esthetic
What are CAD-CAM?
Computer aided design - computer aided manufacture
CAD-CAM come in blocks that need to be milled. The types of blocks are:
- pre sintered
- sintered
What are pre-sintered blocks?
final firing is required prior to delivery bc initially fired at temperature lower than final sintering temp
