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84 Cards in this Set

  • Front
  • Back
The expansion of the investment material must (equal/be greater than/be less than) the shrinkage of the casting alloy on cooling to get precise duplication
equal
What process must occur after the restoration has been cast but before finishing and polishing?
pickling
What type of investment material is used with high noble alloys?
Gypsum-bonded
Gypsum bonded investment is used with what kind of metals?
high noble
What type of investment material is used for metal-ceramic alloys?
phosphate-bonded
What type of investment material is used for some base metal alloys and pressable ceramics?
phosphate-bonded
Put these steps in order

A. Master die prep
B. Burnout
C. Casting
D. Wax pattern formation
E. Cavity/tooth prep
F. Impression of prep
G. Investment of pattern
H. Finish and delivery
E, F, A, D, G, B, C, H
What type of investment material is used for removable partial denture framework made from PB alloys?
ethyl silicate-bonded investment
As of spring 2011, which of these investments is not used at the OUCOD?

A. Gypsum-bonded
B. Phosphate-bonded
C. Ethyl Silicate-bonded
C. Ethyl silicate-bonded
Investments are named based on what component?
The binder (ex: the binder in gypsum-bonded investment is gypsum)
Which type (1, 2 or 3) of Gypsum-bonded investment uses thermal expansion?
type 1
Which type (1, 2 or 3) of Gypsum-bonded investment uses hygroscopic expansion?
type 2
Which type (1, 2 or 3) of Gypsum-bonded investment is used in construction of partial dentures made of high noble alloy
type 3
Gypsum-bonded investment is used to cast ___ noble alloys that have a MELTING range (more/less) than 1000C and a burnout temp of (more/less) than 700C
high, less, less
For gypsum-bonded investment materials, the melting temp of the alloy should be less than ___C and burnout temperature should be less than ____C
1000, 700
What is the chemical name for gypsum?
Calcium sulfate hemihydrate (or alpha-hemihydrate)
What is the binder in gypsum-bonded investment?
gypsum (or Calcium sulfate hemihydrate (or alpha-hemihydrate))
The binder in gypsum-bonded investment forms what % of the material?
25-45
The binder (contracts/expands) between 200C and 400C, (contracts/expands) slightly between 400C and 700C, and then above 700C, a large (contraction/expansion) occurs
contract, expands, contracts
If you excede a temperature ___C, you must redo the process
700
The binder in gypsum-bonded investment decomposes above ___C
700
What type of gases are formed when gypsum decomposes?
sulfer (such as sulfer dioxide)
What causes the "alligator skin" appearance on the casting?
investment was heated above 700C which results in a brittle casting
True or False, the "alligator skin" can be removed by pickling
False
What component of the investment is used to increase rigidity and strength?
binder
What component of the investment is added to counteract the contraction of alpha-hemihydrate (aka gypsum)?
refractory (ex: SiO2/silica)
What is an example of a refractory in gypsum-bonded investment?
Silica (SiO2)
What are the three crystalline allotropic forms that silica exists in?
quartz, crisobalite, tridymite
SiO2 exists in 1 amorphous allotropic form, name this.
amorphous silica
Which of these forms of crystalline allotropic silica is not often used?

A. Quartz
B. Cristobalite
C. Tridymite
C. Tridymite
Which of these forms of crystalline allotropic silica causes expansion at low temperatures (200-270C)?

A. Quartz
B. Cristobalite
C. Tridymite
B. Cristobalite
Which of these forms of crystalline allotropic silica causes rapid expansion between 500-600C?

A. Quartz
B. Cristobalite
C. Tridymite
A. Quartz
Refractory particle (size/distribution) affects roughness, where (size/distribution) affects density and porosity
size, distribution
True or False, if the investment has greater particle size (and thus higher roughness) then the casting will be rougher too
True
What is the purpose of a modifier?
-Provide nonoxidizing atmosphere in mold during casting
-regulate setting expansion and setting time, counteract gypsum above 300C
-coloring agent
Modifiers are (reducing/oxidizing) agents
reducing
Modifiers counteract gypsum above ___C
300
Which component of the investment is colored?
modifier
C and powdered Cu in modifiers have what effect on the investment?
reducing agents that provide a nonoxidizing atmosphere in mold during casting
True or False, burnout temperature is jumped from cool to hot very quickly to achieve desirable results
False, it is ramped up over time
The microstructure of cristobalite reveals (large/small) silica particles, and (cone/rod/spherical) cristobalite particles
large, rod
What is the setting time range for gypsum-bonded investments?
5-25 minutes
What is the normal setting expansion % for type 1 gypsum bonded investments in AIR?
0.1-0.6%
With a lower W/P ratio in gypsum-bonded investments, you get (increased/decreased) exothermic heat which results in a (higher/lower) setting expansion
increased, higher
If you have thinner pattern walls, you'll have a (higher/lower) setting expansion
higher
If you use softer inlay wax, you'll have (higher/lower) setting expansion
higher
Hygroscopic expansion is (greater/less) than normal thermal expansion in air
greater
Where does setting take place with hygroscopic expansion?
water
Hygroscopic expansion is greater than or equal to (2/3/4/5/6/7) times more than normal
6
According to ADA spec. no. 2, hygroscopic setting expansion should be limited to what %?
1.2-2.2%
What three things might cause expansion in hygroscopic expansion?
-crystal interlocking
-hydrostatic pressure in water during setting
-capillary action
Finer silica particles leads to (higher/lower) hygroscopic expansion
higher
In hygroscopic expansion, a higher W/P ratio leads to (higher/lower) setting and thermal expansion
lower
In hygroscopic expansion, if you immerse before initial set, you'll get (higher/lower) expansion
higher
In hygroscopic expansion, confinement means you have no ring liner. Does this have a greater or lower effect on expansion?
greater
The amount of water added is (proportionally/inversely) related with hygroscopic expansion
proportional
Which of these has the LEAST amount of thermal expansion?

A. Average mix
B. Thinner mix
C. Less spatulation
D. Aged investment (let set overnight)
D. Aged investment
Which of these has the MOST amount of TOTAL expansion?

A. Specimen set under dry condition, no wet liner
B. Specimen set surrounded by wet liner
C. Specimen set while immersed in water
C. Specimen set while immersed in water

(see chart, page 5.1)
Which of these has the MOST amount of SETTING expansion (at 2 hrs)?

A. Specimen set under dry condition, no wet liner
B. Specimen set surrounded by wet liner
C. Specimen set while immersed in water
C. Specimen set while immersed in water

(see chart, page 5.1)
Which of these has the MOST amount of THERMAL expansion (at 1200F)?

A. Specimen set under dry condition, no wet liner
B. Specimen set surrounded by wet liner
C. Specimen set while immersed in water
A. Specimen set under dry conditions, no wet liner
ADA Spec no. 2 limits thermal expansion as follows:

Type 1 - ____ % at ___C
Type 2 - ____ % at ___C
Type 1 - 1.0-1.6% at 700C
Type 2 - 0.0-0.6% at 500C
True or False, W/P ratio can affect thermal expansion
True
True or False, it is acceptable to manually or mechanically mix investment material
False, always mechanically mix
What are three reasons you should mix the investment in a partial vacuum?
-Provide better reproduction of surface detail
-Increase the tensile strength of the investment material
-Results in fewer and smaller porosites (voids)
For most investment material, shorter mixing time results in (more/less) expansion
less
What type of investment material is used to cast metal-ceramic alloys that have a high melting range?
phosphate-bonded
What are the components of the powder in phosphate-bonded investment?
90% SiO2 (cristobalite or quartz form),

3% MgO

7% NH4H2PO4
What is unique about the liquid in phosphate-bonded investments?
You select the percentage of water to silica sol
Pure water in phosphate-bonded investments gives you (maximum/minimum) expansion
minimum
What molecule is released in the setting reaction of phosphate-bonded investments?
NH4
Phosphate-bonded investments are (more/less) strong and (more/less) rough than gypsum
more, more
A reaction at higher temperature (increases/decreases) strength and (does/does not) affect surface roughness [in reference to phosphate-bonded investment]
increases, does
In phosphate-bonded investments, roughness increases as burnout temperature is increased from ___C to ___C
1300-1800
What type of investment is used to cast predominantly base metal partial denture alloys having high melting ranges that require investments capable of withstanding temperatures between 1090 and 1180
silicate-bonded
What is the powder composition of silicate-bonded investments?
SiO2

MgO

other glasses and refractory oxides in small amounts
What are the 4 components of the liquid in silicate-bonded investments?
ethyl silicate

denatured ethyl alcohol

stabilized colloidal silica (sometimes)

wetting agent (reduces bubbles on wax)
What is the purpose of the wetting agent in silicate bonded investments?
to reduce formation of bubbles on wax
True or False, air bubbles create nodules on casting that can usually be ground away
FALSE, air bubbles do create nodules, but they can't be ground down without doing damage to the casting
Green strength is also known as ___ strength
wet
What does it mean when something has low wet (aka green) strength?
The first hour or so it is very weak and prone to cracking. Once it's dry, it's fine.
True or False, silicate bonded investments have a low wet/green strength
True
In silicate bonded investments, vibration of mold causes (bigger/smaller) particles and liquid to rise and makes ring susceptible to cracking by evaporation of ___
smaller, alcohol
In the setting reaction for silicate bonded investments, the ___ reverts to cristobalite on heating
binder (silica gel)
In silicate-bonded investments, only thermal (contraction/expansion) occurs
expansion