Week 8- Zirconia

Question 1

Why are zirconia crowns often chosen over PFM and gold?

Answer 1

• Super strength
• Durability
• Excellent aesthetics

Question 2

What is shoulder better than chamfer for zirconia?

Answer 2

Shoulder can be picked up better by scanning device. Chamfer is fine for gold but for zirconia would fracture.

Question 3

What are disadvantages of zirconia crown?

Answer 3

• Wear of opposing teeth
• Wear adjacent teeth (teeth move slightly while eating which creates wear and opening of contact)
• Used to be less aesthetic (bone-white)

Question 4

What can happen if zirconia bonded to emax is use for bridges?

Answer 4

Provides good aesthetics & strength but over time as bridge flexes, the material can debond from each other.

Question 5

What is the new, more aesthetic zirconia?

Answer 5

High translucency zirconia

Question 6

What is the issue with high translucency zirconia?

Answer 6

Strength decreases (still stronger than emax)

Question 7

What happens if pt with PFM crown has bruxism?

Answer 7

At gingival level, tooth crown flexes and over time the ceramic debonds.

Question 8

What can happen if you adjust PFM crowns?

Answer 8

Metal can show through

Question 9

What are advantages of zirconia crowns?

Answer 9

• Metal free which prevents darkening around gingival area
• Can accurately match colour of pts natural teeth due to translucent nature
• Can be conventionally cemented in place (unless short tooth prep)
• Computer aided design and manufacturing- precise fit and less adjustment required
• Highly biocompatible (smooth surface reduces plaque accumulation)
• Promotes healthy tissue response
• Suitable for pt with metal allergies

Question 10

Why is PFM less aesthetic than zirconia in photgraphs?

Answer 10

• PFM: light is directly reflected back to camera
• Zirconia: light is absorbed and reflected back in different directions

Question 11

What are the 3 types of zirconia?

Answer 11

• Solid zirconia (not very translucent)
• Layered zirconia (placement of emax over zirconia)
• Zirconia HT

Question 12

When is monolithic solid zirconia used?

Answer 12

If you need a posterior crown or bridge that requires minimal clearance or to stand up to severe bruxer. Virtually unbreakable.

Question 13

How are solid zirconia restorations made?

Answer 13

Designed and milled with CAD/CAM, then sintered for over 6 hours at 1500°C

Question 14

What happens if you don’t polish zirconia after adjustment?

Answer 14

There will be significant wear of opposing teeth

Question 15

Issue with short zirconia crown (not in occlusion)?

Answer 15

Opposing tooth will over erupt and cause occlusal problems.

Question 16

What is Zirconia HT used for?

Answer 16

Anterior and posterior crowns and bridges up to 3 units.

Question 17

What are characteristics of Zirconia HT?

Answer 17

• Superb aesthetics
• Natural and vibrant translucency
• 590-720 flexural strength (stronger than PFM and Emax but not as strong as solid or layered zirconia)

Question 18

How can you remove cemented zirconia crown?

Answer 18

Drill buccal, occlusal and lingual surface and flick off with flat plastic

Question 19

What is opalite II and its benefits?

Answer 19

Monolithic translucent zirconia

• Less prep and more aesthetic than PFM
• No risk of delaminating
• Exceptional flexural strength- virtually unbreakable
• 15 year warranty

Question 20

What are dimensions for anterior zirconia prep?

Answer 20

Incisal: 1-1.5mm

1mm shoulder

Question 21

What patients is HT zirconia not recommended in?

Answer 21

Pts with bruxism

Question 22

What are dimensions for posterior zirconia prep?

Answer 22

Occlusal: 1.5-2mm

1mm shoulder

Question 23

Issue with layered zirconia

Answer 23

• More expensive
• Risk of ceramic (emax) debonding from zirconia