Anterior All Ceramic Crown Materials (Seghi lecture)

Question 1

What are the dimensions of an ACC prep?

Answer 1

Incisal = 1.5-2mm
Axial = 1 mm lingual and 1.2-1.5 on the facial (depending on technique and materials used)
90’-100’ shoulder
More rounded line angles

Question 2

How does the variability of an ACC compare to an MCC?

Answer 2

The variability can be a bell curve (most are in the middle, some high and some low)
With an ACC, the bell curve shifts to the right
-so higher quality ACCs are higher than MCC
-less esthetic ACCs are still higher than poor MCCs
ACCs have a more consistent outcome

Question 3

Where does strength reinforcing come from in different ACC materials?

Answer 3

It comes from adding more fillers

Question 4

What can strength mechanisms be effected by?

Answer 4

Defects
Crystal Reinforcement
Chemical Strengthening
Stress-induced Transformation
Glazing
Preventing stress corrosion

Question 5

Crack blunting/deflection

Answer 5

A mechanism of crystalline reinforcement
More crystalline material means higher strength
Deflects crack during progression
Slows down the crack growth process by interfering with crack path
With more crystals, it takes more time and energy for a crack to travel far

Question 6

Transformation toughening

Answer 6

Stress induces zirconia crystals to transform from one lattice state to a different lattice state, which increases volume of the crystals, thus closing the cracks between them

Question 7

How do strength and opacity relate?

Answer 7

Increasing opacity correlates with increased strength (thus increasing translucency means less strength)

Question 8

Yttria stabilized Zirconia

Answer 8

Obtaining stable sintered zirconia is difficult due to large volume change accompanying the translation from tetragonal to monoclinic zirconia.
So we stabilize tetragonal zirconia by adding Y
Y is larger than Zr, so we can get closer to ideal lattice size

Question 9

What form of Zirconia has the largest lattice volume?

Answer 9

Monoclinic (140.76 A)

tetragonal is 67.33 A

Question 10

What are the 3 ways to make an All-Ceramic Crown?

Answer 10

Metal-Ceramic Like
Minimal Cutback
Moderate strength translucent ceramics

Question 11

Metal-Ceramic Like ACC

Answer 11

High strength opaque structure

Question 12

Minimal Cutback ACC

Answer 12

Cut back some of the incisal edge and add porcelain to have a more translucent incisal edge

Question 13

Moderate strength translucent ceramics

Answer 13

Whole crown made out of ceramic with some translucent stains

Question 14

Stress Corrosion

Answer 14

Mechanism by which the strength of ceramics is reduced by a moist environment
Caused by the reaction of water at the area around the crack tip, resulting in an increase in crack size

Question 15

What is the reaction that causes stress corrosion?

Answer 15

Strained SiO bonds are more susceptible to a water attack

The water causes hydroxyl groups to form on the surface, which splits the SiO to two SiOH molecules

Question 16

How can stress corrosion form?

Answer 16

Under function, a load is applied
Stress occurs at the underside of the crown
Existing cracks are strained
Water enters and reacts
Crack extends over time

Question 17

What can you do to prevent or delay stress corrosion?

Answer 17

Metal substructure
Reduce more tooth structure
Use stronger/stiffer ceramics

Question 18

How does more tooth reduction prevent stress corrosion?

Answer 18

Creates a thicker cross-section and lower streses

Question 19

What are the different contact initiated failures?

Answer 19

Partial cone cracks
Cone cracks
Median cracks
Chipping

Question 20

What is an example of an interface initiated fracture?

Answer 20

Radial crack

Question 21

Radial crack

Answer 21

Fractures that occur when under stress on the underside of the crown
Newer high ceramic crowns fail because of these

Question 22

Early studies show weaker ceramics had high failure rates where?

Answer 22

In posterior teeth

Question 23

How do the failure rates of MCC compare in anteriors and posteriors

Answer 23

Have about the same 5 yr survival in the posterior and the anterior

Question 24

How do the failure rates of feldspathic porcelains compare in anteriors and posteriors?

Answer 24

Anteriors have a higher 5 yr survival rate than posteriors

Question 25

How do the failure rates of reinforced silica based G-C compare in anteriors and posteriors?

Answer 25

Anteriors have a slightly higher 5 yr survival rate than posterios

Question 26

How do the failure rates of Glass-infiltrated Ceramics compare in anteriors and posteriors?

Answer 26

Anteriors have a slightly higher 5 yr survival rate than posterios

Question 27

How do the failure rates of Dense Sintered Zirconia compare in anteriors and posteriors?

Answer 27

Anteriors have a slightly higher 5 yr survival rate than posterios