Dental Materials: Zirconia

Question 1

Benefits of Zirconia crowns

Answer 1

• 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

Question 2

What is the metal of zirconia?

Answer 2

zirconium

Question 3

How strong is zirconium?

Answer 3

Similar to titanium

Question 4

How is cubic zirconium formed?

Answer 4

When white zirconium dioxide is heated to very high temperaturesW

Question 5

What is another word for tetragonal zirconium?

Answer 5

Zirconium dioxide

Question 6

Cubic zirconium is ____________ in nature, but can be synthesized to a very hard, optically flawless, and colorless gemstone.

Answer 6

rare

Question 7

What are the 3 phases of zirconia?

Answer 7

1. monoclinic
2. tetragonal
3. cubic

Question 8

What is cubic zirconia?

Answer 8

cubic crystalline form of ZrO2
- has optical properties like diamond

Question 9

What is dental zirconia?

Answer 9

modified yttria tetragonal zirconia polycrystal

Question 10

Why is yttria added?

Answer 10

Stabilize the crystal structure transformation during firing at an elevated temperature

Question 11

What is the tetragonal phase for?

Answer 11

toughness (strength)

Question 12

What is the cubic phase for?

Answer 12

translucency (esthetics)

Question 13

Which phase of zirconia is not useable for dentistry?

Answer 13

Monoclinic

Question 14

What is the amount of yttria in tetragonal zirconia?

Answer 14

3% yttria
high strength zirconia

Question 15

What is the amount of yttria in cubic zirconia?

Answer 15

> 5% yttria
“esthetic” high translucency zirconia

Question 16

What does yttria content determine?

Answer 16

strength and translucency by adjusting phase composition

Question 17

Yttria ________ tetragonal polycrystals.

Answer 17

Stabilized

Question 18

As yttria percentage increases, the ___________ increases, but the _____________ decreases.

Answer 18

1. translucency
2. strength

Question 19

Which is the most opaque zirconia?

Answer 19

3% yttria zirconia
mainly tetragonal zirconia

Question 20

Which is the most translucent zirconia?

Answer 20

5% yttria zirconia
more cubic/ess tetragonal phase

Question 21

What percentage yttria results from tetragonal and cubic phases?

Answer 21

4%

Question 22

How does the tetragonal phase function to improve strength?

Answer 22

When faced with force, instead of shattering, turns into monoclinic crystal (harder)
hinder crack propagation

Question 23

What is transformation toughening?

Answer 23

When tetragonal particles that normally constitutes Zirconia transform into a stronger monoclinic particle in response to cracks, so the crack does not propagate

Question 24

Do all zirconia generations have the transformation toughening property?

Answer 24

No
cubic zirconia does not have this ability

Question 25

Why does 3% yttria have low transparency?

Answer 25

scatter/refract at smaller tetragonal crystal boundaries

Question 26

Why does 5% yttria have high transparency?

Answer 26

reducing light scattering and deflection
larger cubic crystals with isotropic optical properties

Question 27

Where is 3Y best in the dental anatomy?

Answer 27

Posterior teeth
due to low transparency and esthetics

Question 28

Where is 5Y best in the dental arch?

Answer 28

Anterior teeth
due to high transparency and esthetic

Question 29

Monolithic zirconia vs. Bilithic Zirconia

Answer 29

Monolithic = one layer (stronger) = 3Y
Bilithic = layers of different ceramic powders (more translucent) esthetic

Question 30

What are CAD-CAM?

Answer 30

Computer aided design - computer aided manufacture

Question 31

CAD-CAM come in blocks that need to be milled. The types of blocks are:

Answer 31

1. pre sintered
2. sintered

Question 32

What are pre-sintered blocks?

Answer 32

final firing is required prior to delivery bc initially fired at temperature lower than final sintering temp