W8 - Zirconia vs PFM - Abbott

Question 1

2 types of zirconia fabrication

Answer 1

Solid full-contour zirconia - monolithic

Layered zirconia - not as popular anymore

Question 2

Why are shoulders better than chamfers for zirconia? (2)

Answer 2

Shoulder can be picked up and analysed by scanning device

Chamfer will not yield thick enough material → will fracture

Question 3

Disadvantages of zirconia crowns

Answer 3

Minimal

Some are skeptical about the hardness → may wear opposing teeth and adjacent teeth

It was originally unaesthetic → dentists put emax on top of zirc for better aesthetics → no need now due to monolithic zirconia

Question 4

Alternative to Emax in anterior teeth

Answer 4

High translucency Zirconia

• Not as strong as conventional zirconia, but still stronger than Emax

Question 5

What can cause the opening of margins and fracturing of ceramics that appear like NCCL’s?

Answer 5

Bruxism

• Pt clenches in edge to edge bite → Teeth flex → enamel or ceramic fractures

Question 6

Zirconia vs PFM aesthetics

Answer 6

Light shines through the translucent nature of the zirconia and transmits back the color of adjacent teeth

Zirc is also metal-free → no darkening around the gingival area or possibility of metal margins with recession

vs

PFM - opaque → doesn’t absorb any of the light. Material bounces the light right back at the camera

“Samsung fridge door” - Abbott

Question 7

What is Layered zirconia?

Answer 7

An older style of zirconia

• Made in attempt to increase aesthetics
• Emax layered on top of zirconia
• Not used much anymore now that we have high translucency zirconia

Question 8

What is “green-stage” zirconia

Answer 8

Zirconia blocks prior to being heated to 1500 degrees for hardening

• Allows for easier cutting during fabrication

Question 9

Advantages of choosing Zirconia

Answer 9

1. Can be coventionally cemented in place
2. Computer-aided design for precise fit → reduced chair-side time for adjustment
3. Highly biocompatible
4. Suitable for pts with metal allergies
5. Promotes a healthy tissue response

Question 10

What is the flexural strength of zirconia HT

Answer 10

590-720 MPA

Question 11

What is the flexural strength of Opalite / Monolithic zirconia?

Answer 11

1100 MPA

Question 12

indications for High Translucent zirconia

Answer 12

Single anterior and posterior crowns

Bridges up to three units

Implants crowns

Question 12

indications for High Translucent zirconia

Answer 12

Single anterior and posterior crowns

Bridges up to three units

Implants crowns

Question 13

When is HT zirconia not recommended?

Answer 13

Bruxism

• Use monolithic instead

Question 14

Preparation guidelines for anterior zirconia crown (3)

Answer 14

1. Sufficient wall thickness (1.0mm and 1.5mm incisor reduction)
2. Clear and continous shoulder at gingival margin (1mm)
3. All incisal edges to be rounded

Question 15

Preparation guidelines for posterior zirconia crown?

Answer 15

1. 1. Sufficient wall thickness (1 mm and 1.5-2.0mm occlusal reduction)
2. Clear and continous shoulder (1mm) around gingival margin
3. Bevel not recommended
4. Round off all sharp points

Question 16

factors that may make a crown prep unacceptable

Answer 16

• no undercuts
• no gutter preparation
• 90 degree shoulder unacceptable
• parallel walls unacceptable
• sharp edges

Question 17

What must you do when drilling zirconia during adjustment

Answer 17

No pressure → will increase heat which can fracture zirconia

Use water

Question 18

Why is layered zirconia not preferred? (2)

Answer 18

More expensive

Can lead to debonding between materials