L4- Metal Ceramic Restorations Flashcards
What are the components of metal based ceramics?
- metal coping
- opaquing porcelain
- body porcelain
- high fusing shoulder porcelain
For PFM, the the metal coupling 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
0.2-0.3mm
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 exceed 2.0 mm of body porcelain?
the porcelain becomes unsupported and risks fracture
The purpose of the 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 mm
Incisal portion: 1.1-1.2 mm
Middle/ body portion: 0.8-0.9 mm
Opaque porcelain: 0.1-0.2 mm
Inside:
Cervical metal: 0.3-0.4 mm
Incisal metal: 0.2-0.3 mm
- Designed with thickness to support the porcelain
- designed to support occlusal and proximal contacts
- Designed with extensions to support porcelain
- Margin design to adapt perfectly to margins and support the porcelain if placed on margins
metal coping
Describe the design of the metal coping in a PFM:
- convex, rounded angles
- ledge of metal to support a 90 degree metal-ceramic finish
Metal ceramic bridge designs need adequate thick in both the ____ and ____ for rigidity to prevent porcelain fracture while also trying to optimize esthetics
pontic & connectors
Starting with a ____ to create the ideal contour and esthetics, 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 is then:
“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 crown is complete
- lower fusing temp than body porcelains
stains/glazes
What does the Identalloy system provide?
percent and type of metals in the substructure of the 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
List the 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 is greater than or equal to 60% with atleast 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 and overcome with new 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
Atleast 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 and greater resistance to deformation?
less gold
List the formations 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/sensitivity
base metal
This property of base metal makes it more difficult to cast and therefore more difficult to finish in preparation for the porcelain and 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 a stress dependent chemical reaction between the ____ & ____ that cause growth and future fracture even with comparatively low occlusal loading over long periods
water vapor & crack tips
- predominately glass
- etchable
- most translucent
- weakest strength
- most esthetic
Feldpathic porcelain
- particle-filled glass ceramic
- increased strength
- less translucent than feldspathic (but not the least)
- etchable
LIthium disillicate
- polycrystalline ceramic
- not etchable
- highest strength
- lowest translucency
zirconia
Feldspathic porcelain has several components including:
- Feldspar (75-85%)
- Quartz (silica)
- Alumina
- Glass modifiers
- Leucite (10-20%)
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 a hard strong oxide that increases strength as well as increases the viscosity of the melt when firing
alumina
Component of feldspathic porcelain:
- Alkali fluxes (mostly potassium & sodium oxides)
- increases the CTE
- includes opacifiers and colorants
glass modifiers
Component of feldspathic porcelain that is the KEY INGREDIENT to increase the 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 temp changes
Porcelains low CTE puts it at risk for:
fracture
_____ 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?
- The bond between the ceramic and the metal substructure
- The compatibility of the metal and the porcelain
- Design and rigidity of the metal comping or framework
The metal porcelain bond in a PFM is accomplished through:
- mechanical interlocking of materials
- Van der Waals forces
- chemical bonding (at molecular level)
- compressive forces
The microabrasiaion from metal finishing or air abrasion:
- clean the surface
- create surface that allow for interlocking of porcelain and metal
- increase the surface area of the metal
- increase wetability
Allows the porcelain to flow over the metal material better and therefore flow into the abraded surface
wetablility
Which of the porcelain layers bonds to the metal coping?
opaque layer (the silica oxide from the porcelain to the onside layer of the metal + VDWF)
