Metal Ceramics Flashcards
\_\_\_\_\_\_\_\_\_ crown consists of a metal casting or coping which fits over the prepared tooth and has ceramic fused to the metal. This combines the strength and accuracy of metal with the esthetics porcelain can provide.
Porcelain Fused to Metal (PFM)
-Designed with thickness to support the porcelain -Design to support occlusal and proximal contacts -Designed with extensions to support porcelain -Margin design to adapt perfectly to margins and support the porcelain if porcelain margins are placed
Metal Coping
The Ledge of metal to support a ____ degree Metal-
Ceramic finish
90 degree
How thick should the metal coping be to support the porcelain?
.3-.5mm thick
metal needs to be at least ______ thick for noble metals
0.3 – 0.5mm
metal needs to be at least _____ thick for base metals
0.2mm
-if porcelain is more than ____ thick, a fracture of the porcelain becomes a higher risk
2 mm
Ideal of ______ thick porcelain means that the metal design will vary and change
to allow for this uniform thickness
1 – 1.5 mm
Masks the metal
Established the metal-ceramic bond
Opaque porcelain
Colors include dentin, enamel, translucent,
shoulder porcelains
Body porcelain
Final color match
Color modification once crown is complete
Lower fusing temp than body porcelains
Stains/Glazes
A high noble metal has at least _____ % gold
40%
The higher the gold content in a metal, the ____ the metal
Softer the metal
At least 25% noble metals but doesn’t have to be GoldPalladium – Silver
Palladium – Copper
Palladium – Cobalt
Palladium – Gallium
They are a compromise between the high noble metals and the base metals in
terms of cost and in density
The workability and fabrication can be similar to high noble
Because of less Gold, noble metals tend to have a higher strength and greater restistance
to deformation.
Noble metals
Nickel-Chromium
Nickel-Chromium-Beryllium
Cobalt-Chromium
Stiffer metal
Harder metal
Greater Sag resistance
Lowest Density – more difficult to cast and therefore more difficult to finish in
preparation for the porcelain and not a strong solder joints
This can also lead to high oxide formation and therefore problems with
bonding
Often the lowest cost and lowest quality of materials.
Higher likelihood of reaction if patient has metal allergy.
Base Metal
PFM crowns are layered with _____ porcelain
Relatively weak material
Wears opposing teeth at a very high rate
feldspathic porcelain
What happens to feldspathic porcelain when it is fired?
Shrinks
What part of the feldspathic porcelain -Increases the Coefficient of Thermal Expansion
-Includes opacifiers and colorants
Glass Modifiers
-Microabrasions from Metal finishing or from Air Abrasion create a
surface that allows for the interlocking of porcelain and metal
-These microabrasions also clean the surface
-These microabrasions also increase the surface area of the metal
-Finally, the microabrasions increase the “Wettability” of the
metal. This means the porcelain will flow over the metal
material better and therefore flow into the abraded surface
-Mechanical Interlocking
-When done correctly, this oxide bond is so strong,
the _____ will break before the bond
gives away!
porcelain
If the ____ is contaminated after firing, the bond will break
Oxide layer
_____ the amount of Gold in the alloy, the lower the melting temperature
Higher
Because some porcelains fuse at a higher temperature than the melting temp of the metal, _______ fusing ceramic is used.
low
fusing
The occlusion between the natural teeth and PFM should put the natural teeth on the ___ portion of the PFm
Metal portion
