Framework Design & Metal Ceramic FPDs

Question 1

What are the three main causes of failure for FPDs?

Answer 1

1. Caries (23%)
2. Porcelain Failure (16%)
3. Uncemented (15%)

Question 2

Optimal Restorations are a balance between _____, ______, and ______ properties.

Answer 2

Biologic
Mechanical
Esthetic

Question 3

True or False: In order to prevent restoration wear, you should minimize sliding contacts and establish anterior guidance.

Answer 3

True

Question 4

True or False: A good way to prevent wear by or of the restoration is to have opposing contacts in different materials.

Answer 4

False: same material = less wear

Question 5

True or False: Porcelain-to-Gold contact is optimal for wear resistance.

Answer 5

False: porcelain-to-gold contact should be AVOIDED!

zirconia has low wear

Question 6

Occlusal contact should be at least ____ mm from metal-porcelain junction.

Answer 6

1.5 mm

Question 7

Glass will adhere to clean, gas-free metal when covered with adherent _______ that partially dissolves into the glass at a high enough temperature.

Answer 7

oxide

Question 8

Glass-to-metal bonding is strain free if (and only if) the ________ are the same over the entire temperature range.

Answer 8

Coefficients of thermal expansion

Question 9

True or False: Without a minimal, yet sufficient, oxide layer, porcelain will not bond to metal.

Answer 9

True. Porcelain will only bond to metal with oxide thin layer

Question 10

What are the two general categories of failure in metal-porcelain bonding?

Answer 10

Cohesive and Adhesive

Question 11

Explain what it would mean if there were an “adhesive failure at the porcelain-metal interface.”

Answer 11

Adhesive failures occur BETWEEN two materials. Without an oxide layer, the metal and porcelain would separate

Question 12

What would cause an ADhesive failure at the oxide-metal interface?

Answer 12

Contaminated metal

Question 13

What would cause an ADhesive failure at the oxide-porcelain interface?

Answer 13

Contaminated oxide

Question 14

What is a cohesive failure?

Answer 14

Cohesive failures occur within a material, not between two different materials.

Question 15

In porcelain-metal bonding, which material determines maximum strength? Why?

Answer 15

Porcelain

-It has the weakest cohesive strength of the three (porcelain, oxide, or metal)

Question 16

Which type of cohesive failure is rare and does not usually occur?

Answer 16

Metal Cohesive Failure

Question 17

What would cause cohesive failure of the oxide layer?

Answer 17

Excessive oxidation

Question 18

What are three advantages to following anatomic contour in a wax-up?

Answer 18

1. Even thickness of porcelain
2. Smooth transition between metal and porcelain
3. Accurate location of junctions

Question 19

What two factors may have caused an insufficient thickness of porcelain?

Answer 19

1. Under-reduction of preparation

2. Excessive metal thickness

Question 20

Why is it important to have rounded internal angles in a preparation?

Answer 20

Stress concentrations will lead to porcelain fracture

Question 21

The Metal-Porcelain junction should be ______ degrees in order to provide adequate strength.

Answer 21

90 degrees

Question 22

True or False: Correct crown fabrication will be designed such that the porcelain wraps-around the cusp tip.

Answer 22

True

Question 23

Proper crown characteristics include a metal thickness of at least ______mm.

Answer 23

0.3 mm