Anterior All Ceramic Crown Materials (Seghi lecture) Flashcards
What are the dimensions of an ACC prep?
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
How does the variability of an ACC compare to an MCC?
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
Where does strength reinforcing come from in different ACC materials?
It comes from adding more fillers
What can strength mechanisms be effected by?
Defects Crystal Reinforcement Chemical Strengthening Stress-induced Transformation Glazing Preventing stress corrosion
Crack blunting/deflection
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
Transformation toughening
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
How do strength and opacity relate?
Increasing opacity correlates with increased strength (thus increasing translucency means less strength)
Yttria stabilized Zirconia
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
What form of Zirconia has the largest lattice volume?
Monoclinic (140.76 A)
tetragonal is 67.33 A
What are the 3 ways to make an All-Ceramic Crown?
Metal-Ceramic Like
Minimal Cutback
Moderate strength translucent ceramics
Metal-Ceramic Like ACC
High strength opaque structure
Minimal Cutback ACC
Cut back some of the incisal edge and add porcelain to have a more translucent incisal edge
Moderate strength translucent ceramics
Whole crown made out of ceramic with some translucent stains
Stress Corrosion
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
What is the reaction that causes stress corrosion?
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
How can stress corrosion form?
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
What can you do to prevent or delay stress corrosion?
Metal substructure
Reduce more tooth structure
Use stronger/stiffer ceramics
How does more tooth reduction prevent stress corrosion?
Creates a thicker cross-section and lower streses
What are the different contact initiated failures?
Partial cone cracks
Cone cracks
Median cracks
Chipping
What is an example of an interface initiated fracture?
Radial crack
Radial crack
Fractures that occur when under stress on the underside of the crown
Newer high ceramic crowns fail because of these
Early studies show weaker ceramics had high failure rates where?
In posterior teeth
How do the failure rates of MCC compare in anteriors and posteriors
Have about the same 5 yr survival in the posterior and the anterior
How do the failure rates of feldspathic porcelains compare in anteriors and posteriors?
Anteriors have a higher 5 yr survival rate than posteriors
How do the failure rates of reinforced silica based G-C compare in anteriors and posteriors?
Anteriors have a slightly higher 5 yr survival rate than posterios
How do the failure rates of Glass-infiltrated Ceramics compare in anteriors and posteriors?
Anteriors have a slightly higher 5 yr survival rate than posterios
How do the failure rates of Dense Sintered Zirconia compare in anteriors and posteriors?
Anteriors have a slightly higher 5 yr survival rate than posterios
