L4: Metal Ceramic Restorations Flashcards
What are the components of metal based ceramics?
- metal coping
- opaquing porcelain
- body porcelain
- high fusing shoulder porcelain
For a PFM the metal coping should be ____ thick when using a noble metal and ____ thick when using a base metal
0.3-0.5 mm
0.2 mm
Where porcelain is not overlayed to the metal coping, the metal should be ___ thick
0.8-1.0 mm
Opaquing porcelain is usually ____ thick
0.2-0.3 mm
Body porcelain is done in ____ and should be _____ thick
layers; 0.8-2.0 mm
List the layers of the body porcelain:
- dentin
- enamel
- translucent
- modifiers
What results when you go beyond the 2.0 mm of body porcelain?
The porcelain becomes unsupported and risks fracture
The purpose of this component of a PFM is to keep the porcelain from shrinking back, creating a gap and leading to fracture risk:
high fusing shoulder porcelain
Label the following PFM:
Incisal porcelain: 1.5-2.0 mm
Incisal portion:
Middle/body portion: 0.8-0.9mm
Opaque porcelain: 0.1-0.2 mm
(inside)
Cervical metal: 0.3-0.4 mm
Incisal metal: 0.2-0.3
-Designed with thickness to support the porcelain
-Designed to support occlusal & proximal contacts
-Designed with extensions to support porcelain
-Margin design to adapt perfectly to margins & support the porcelain if placed on margins
metal coping
Describe the design of a metal coping in a PFM:
- convex, rounded angles
- ledge of metal to support a 90 degree metal-ceramic finish
Metal ceramic bridge designs needs adequate thickness in both the ____ & ____ for rigidity to prevent porcelain fracture, while also trying to optimize esthetics
pontic & connectors
Starting with a ____ to create the ideal contour & esthetic, a metal coping is then designed based on the desired porcelain thickness. This metal is then ____ at ____ or ____
wax up; cast at 2300-2600 degrees or milled
Once the metal coping is made, the porcelain:
“stacked” onto coping in layers
Masks the metal & establishes the metal-ceramic bond:
opaque porcelain
Colors include, dentin, enamel, translucent and shoulder porcelains:
body porcelain
The final color match/modification once the crown is complete; lower fusing temp than body porcelains:
stains/glazes
What does the Identalloy system sticker provide?
Percent & type of metals in the metal substructure crown
Au-PT-Pd:
gold-platinum-palladium
Au-Pd-Ag:
gold-palladium-silver
Ni-Cr-Be:
nickel-chromium-beryllium
What are the classifications of the metals used in the metal substructure of a PFM:
- high noble
- noble
- base metal
Desirable characteristics of metal ceramic alloys:
- biocompatibility
- accuracy of fit
- HIGH modulus of elasticity
- HIGH yield strength
- HIGH resistance to deformation
- EASILY soldered
Noble metal content greater than or equal to 60% with at least 40% of the content being gold:
High noble metals
gold-platinum-palladium
gold-palladium-silver
gold-palladium
These are all considered:
high noble metals
What happens if the metal substructure contains too much gold?
sag
In gold-palladium-silver, what issue did we run into with the silver?
The silver used to discolor some porcelains in a process called greening. This problem is mostly gone & overcome with news formulations
When silver discolors porcelain:
greening
Benefits of gold-palladium:
What component is at a higher percentage?
- resistant to sag
- excellent working properties
Gold (45-55%)
What formulation is what we use in our PFMs at UMKC?
Gold-palladium
Resistance to deformation at high temperatures with good yield strength and a high modulus of elasticity:
Sag
At least 25% noble metals, but doesn’t have to be gold:
noble metals
List the formulations of noble metals:
Palladium-silver
Palladium-copper
Palladium-cobalt
Palladium-gallium
Noble metals are a compromise between the high noble metals and the base metals in terms of:
- cost
- density
What aspect of noble metals tends to contribute to having higher strength & greater resistance to deformation?
Less gold
List the formatulations of base metals:
- nickel-chromium
- nickel-chromium-beryllium
- cobalt-chromium
-stiffer metal
-harder metal
-greater sag resistance
-lowest density
-often lowest cost
-high likelihood of reaction/sensitiity
Base meta;
This property of base metal makes it more difficult to cast & therefore more difficult to finish in preparation for the porcelain & not able to create strong solder joints:
lowest density
The lowest density property of base metal can also lead to high oxide formation and therefore problems with:
bonding
With base metals, the lab tech handling the ____ is at risk due to carcinogenicity
Beryllium
PFM crowns are layered with:
Feldspathic porcelain
Feldspathic porcelain is brittle, meaning the _____ strength is better than the ____ strength
compressive; tensile
With feldspathic porcelain on a PFM, there is stress dependent chemical reaction between ____ & ____ that cause growth & further fracture even with comparatively low occlusal loading over long periods
water vapor & crack tips
-Predominately glass
-etchable
-most translucent
-weakest strength
-most esthetic
Feldspathic porcelain
-particle-filled glass ceramic
-etchable
-increased strength
-less translucent than feldspathic (but not the least)
Lithium discilicate (e.Max & Empress)
-polycrystalline ceramic
-not etchable
-highest strength
-lowest translucency
Zirconia
Feldspathic porcelain has several components including:
- Feldspar (75-85%)
- Quartz (silica_
- Alumina
- Glass modifiers
- Leucite
Component of feldspathic porcelain responsible for forming the glass matrix:
Feldspar
Component of feldspathic porcelain creating the framework around which other components flow:
Quartz
Component of feldspathic porcelain which is a hard, strong oxide that increases strength as well as increase the viscosity of the metal when firing:
Alumina
Components of porcelains:
-alkali fluxes (mostly potassium & sodium oxides)
-increases coefficient of CTE
-includes opacifiers & colorants
Glass modifiers
Component of feldspathic porcelain that is the KEY INGREDIENT to increase CTE to bring ceramic closer to the CTE of metal:
Leucite (10-20%)
Porcelain has a low CTE meaning:
It doesn’t expand/contract in response to temperature changes
Porcelains low CTE puts it at risk for:
fratcure
____ increases the CTE of porcelain, making it more fracture resistant
leucite
We want metal CTE to be ____ compared to the porcelain CTE
lower
(because if the metal expands too much under the porcelain it will cause fracture to the porcelain)
Where does the strength of the PFM come from?
- bond between the ceramic and the metal substructure
- compatibility of the metal & porcelain
- design & rigidity of the metal coping or framework
The metal-porcelain bond in a PFM is accomplished through:
- mechanical interlocking of materials
- Vander Waal’s forces
- chemical bonding (at molecular level)
- compressive forces
The microabrasions from metal finishing or air abrasion:
- clean the surface
- create surface that allows for interlocking of porcelain & metal
- increase surface area of metal
- increase wearability
Allows the porcelain to flow over the metal material better and therefore flow into the abraded surface:
wetability
Which of the porcelain layers bonds to the metal coping?
Opaque layer
(the silica oxide from the porcelain with the oxide layer of the metal + VDWF)
