All-Ceramics I Flashcards
What is the main indication of an ACC
optimize esthetics
What are five contraindications of an ACC
parafunctional activity
insufficient support from tooth preparation
insufficient porcelain thickness in lingual aspect
opposing teeth that occlude with cervical fifth of crown
short cervical crowns
What are three advantages of an ACC
best esthetics
best color stability
some ACC systems can be bonded to natural tooth structure
What is a main disadvantage of an ACC
CATASTROPHIC FAILURE due to weak strength and brittle nature of ceramics
What are four disadvantages of an ACC
higher laboratory costs (more so 10 years ago)
more tooth reduction is required
cementation can be complicated
may have poorer marginal adaptation
What are the two silica based ceramics
feldspathic ceramics
hot-pressed glass ceramics
What are two types of hot-pressed glass ceramics
leucite reinforced glass ceramic
lithium dislocate reinforced glass ceramic
What are two non-sillica based ceramics
slip-cast, glass infiltrated ceramic (alumina, alumina/zirconia and magnesium alumina)
polycrystalline “densely sintered” alumina and zirconia
What are the characteristics of bonding silica based ceramics
can AND must bond with resin to improve strength
What are the characteristics of bonding non-silica based ceramics
difficult to bond but strong enough to use conventional cements
What are the four components of dental feldspathic porcelain
feldspar; potassium and sodium aluminosilicates
quartz
ceramic oxides (color and shade)
20% leucite crystals
Dental feldspathic porcelain is headed to a glassy molten mass (around 2000℉) and quenched to form what
a “frit” and ground into a fine powder
Dental porcelain is mostly what
glassy with a small amount of leucite crystals (12%)
Leucite has a much higher what than glass
thermal expansion
Why is leucite need to make the bonding to metal possible
leucite has a much high coefficient of thermal expansion (CTE) than glass, the addition of the crystals raises the CTE of the porcelain so that it is slightly lower than that of metal in order to place the ceramic under slight compression; enhancing the durability of the porcelain to metal bond
Ceramic materials are susceptible to what kind of fracture
brittle
What happens to the properties of ceramics under tension and compression
ceramics are weaker when in tension and stronger when under compression
Leucite crystalline reinforcement strengthens the ceramic how
by resisting crack propagation via deflection of the advancing crack
How does the leucite crystal cause crack deflection to occur
the higher CTE (and contraction) of the leucite crystals compared to the glassy matrix results in a layer of glass under compression immediately adjacent to the crystal; the stronger layer within the glassy matrix deflects the advancing matrix
This type of dental porcelain is the high concentration of ceramic and metal oxides that block out metal substructure
opaque
This type of dental porcelain is more translucent, with some oxide pigments
body or dentin
This type of dental porcelain is very translucent, no oxides
enamel or incisal
What is the composition of modern dental feldspathic porcelain
feldspathic glass containing 20% leucite
dental feldspathic porcelain offers great esthetics, why?
it is very translucent due to high glass content
What is the strength of dental feldspathic porcelain
relatively low, (60-80MPa) due to lower crystalline phase
Recently, lower-fusing dental feldspathic porcelains containing <10% leucite with smaller particle size have been developed and have shown what
low enamel wear and higher strength
What is the size of leucite particles of conventional feldspathic porcelain
20-30μm
What is the translucency of stacked dental feldspathic porcelain
highest translucent (superior esthetics) of any dental ceramic
What are two indications for stacked dental feldspathic porcelain
layering porcelain for metal and ACCs
feldspathic porcelain veneers
What are two disadvantages of stacked dental feldspathic porcelain
low strength
translucency prevents masking of discolored teeth
What are four reasons that ceramics fail
brittle fracture
initiated from internal surface
cyclic fatigue (low loads, many cycles)
stress corrosion
What is the difference between brittle fracture in metals vs. ceramics
in metals, the atoms slide past each other (dislocation slip)
in ceramics, the bonds between atoms break (Griffiths flaws)
Where does the propagation of a fracture of ceramic initiate
from the interior to the exterior (inside → out) due to tension
You can strengthen porcelain with this but interface initiated fractures are difficult but contact fractures are still present
metal substructure
What are the two development strategies of ACCs
develop stronger materials to substitute for metal and veneer with feldspathic porcelain
develop high strength translucent materials that can be used in full thickness or minimal reduction
Always do this to porcelain, or it will crack
polish, do not leave it rough
Which type of ACC, monolithic, minimal cutback, or layered substructure, has the most feldspathic porcelain
layered substructure
