Fixed Pros

Question 1

What is the effect of adding leucite crystals to leucite reinforced ceramic?

Answer 1

Leucite increases the strength of the ceramic

Question 2

What percentage crystals is lithium disilicate?

Answer 2

70%

Question 3

How does the amount of glass in a material affect its strength?

Answer 3

Increased glass content = decreased strength

Question 4

How is lithium disilicate bonded?

Answer 4

Etch for 10-20 sec with 5-9% HF acid
Silane coupling agent
Resin bond

Question 5

How does over-etching lithium disilicate affect its strength?

Answer 5

Overetching weakens material

Question 6

How does a silane primer work?

Answer 6

Organic component of silane bonds to resin, inorganic component bonds to etched ceramic

Question 7

What is the full name for zirconia used in dentistry?

Answer 7

Partially stabilised tetragonal zirconia polycrystal

Question 8

What are the two phases that zirconia exists in?

Answer 8

Monoclinic = at room temperature, most stable phase
Tetragonal = unstable phase but stronger.

Question 9

How is zirconia stabilised?

Answer 9

Yttrium oxide is added so that it remains in tetragonal phase

Question 10

Describe transformational toughening.

Answer 10

When a crack propagates in zirconia, it is converted from monoclinic phase to tetragonal phase. Monoclinc phase zirconia has higher volume crystal particles. Therefore the crack is “squeezed shut” and does not propagate further.

Question 11

Why is zirconia initially milled larger than required?

Answer 11

Shrinkage 25-30% occurs on sintering.

Question 12

What is the issue with layering zirconia with porcelain?

Answer 12

High rate of failure at zirconia-porcelain interface due to different rates of cooling after sintering.
Fix: allow to cool very very slowly

Question 13

Is zirconia bondable?

Answer 13

No - relies on retention and resistance forms for bonding

Question 14

Ductility definition

Answer 14

Ability of a metal to withstand tensile stress before fracturing

Question 15

Proportional limit

Answer 15

Maximum point at which stress is proportional to strain. After which plastic deformation occurs

Question 16

Yield point

Answer 16

Point at which permanent deformation occurs

Question 17

Describe the classification of metals used for fixed pros.

Answer 17

Precious: >60% precious, >40% gold
Semi precious: >25% precious, no gold requirement
Base metal alloy: <25% precious

Question 18

What is the difference in resin bonding between precious metal and base metal alloy materials

Answer 18

Base metal alloys can bond to resin easily due to oxide layer formation. Precious metals are non-bondable

Question 19

What is the difference in ceramic bonding between precious metals and base metal alloys?

Answer 19

Gold bonds easily to ceramic. Base metal alloys don’t bond to ceramic

Question 20

What are the affects on fit of beveling?

Answer 20

Increased seal but worse seat

Question 21

What are 3 methods of improving cement escape

Answer 21

1. Die spacer - technician paints layer of die spacer over model everywhere except margin. When crown cast, it leaves small gap for cement
2. Vent at top of crown
3. Using a lower viscosity cement

Question 22

2

What are the primary factors affecting retention?

Answer 22

1. Taper - ideally 6%, but 10-20% OK. Increased taper = decreased retention
2. SA - increased SA = increased retention

Question 23

2

What are the secondary factors affecting retention?

Answer 23

Surface texture
Cement/bond used

Question 24

What are the two temporary cements?

Answer 24

ZOE
Polycarboxylate

Question 25

7

What are the characteristics of an ideal cement?

Answer 25

low film thickness
high compressive strenght
long working time
short setting time
low solubility
low microleakage
easy clean up

Question 26

What are 3 strategies to increase micromechanical retention?

Answer 26

Use etchable ceramics - HF acid 5-9%
Sandblasting non-etchable materials e.g zirconia and metals
Increased surface area