Applied Dental Materials 1 Lecture 7 (Casting Materials)

Front 1

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

Back 1

equal

Front 2

What process must occur after the restoration has been cast but before finishing and polishing?

Back 2

pickling

Front 3

What type of investment material is used with high noble alloys?

Back 3

Gypsum-bonded

Front 4

Gypsum bonded investment is used with what kind of metals?

Back 4

high noble

Front 5

What type of investment material is used for metal-ceramic alloys?

Back 5

phosphate-bonded

Front 6

What type of investment material is used for some base metal alloys and pressable ceramics?

Back 6

phosphate-bonded

Front 7

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

Back 7

E, F, A, D, G, B, C, H

Front 8

What type of investment material is used for removable partial denture framework made from PB alloys?

Back 8

ethyl silicate-bonded investment

Front 9

As of spring 2011, which of these investments is not used at the OUCOD?

A. Gypsum-bonded
B. Phosphate-bonded
C. Ethyl Silicate-bonded

Back 9

C. Ethyl silicate-bonded

Front 10

Investments are named based on what component?

Back 10

The binder (ex: the binder in gypsum-bonded investment is gypsum)

Front 11

Which type (1, 2 or 3) of Gypsum-bonded investment uses thermal expansion?

Back 11

type 1

Front 12

Which type (1, 2 or 3) of Gypsum-bonded investment uses hygroscopic expansion?

Back 12

type 2

Front 13

Which type (1, 2 or 3) of Gypsum-bonded investment is used in construction of partial dentures made of high noble alloy

Back 13

type 3

Front 14

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

Back 14

high, less, less

Front 15

For gypsum-bonded investment materials, the melting temp of the alloy should be less than ___C and burnout temperature should be less than ____C

Back 15

1000, 700

Front 16

What is the chemical name for gypsum?

Back 16

Calcium sulfate hemihydrate (or alpha-hemihydrate)

Front 17

What is the binder in gypsum-bonded investment?

Back 17

gypsum (or Calcium sulfate hemihydrate (or alpha-hemihydrate))

Front 18

The binder in gypsum-bonded investment forms what % of the material?

Back 18

25-45

Front 19

The binder (contracts/expands) between 200C and 400C, (contracts/expands) slightly between 400C and 700C, and then above 700C, a large (contraction/expansion) occurs

Back 19

contract, expands, contracts

Front 20

If you excede a temperature ___C, you must redo the process

Back 20

700

Front 21

The binder in gypsum-bonded investment decomposes above ___C

Back 21

700

Front 22

What type of gases are formed when gypsum decomposes?

Back 22

sulfer (such as sulfer dioxide)

Front 23

What causes the "alligator skin" appearance on the casting?

Back 23

investment was heated above 700C which results in a brittle casting

Front 24

True or False, the "alligator skin" can be removed by pickling

Back 24

False

Front 25

What component of the investment is used to increase rigidity and strength?

Back 25

binder

Front 26

What component of the investment is added to counteract the contraction of alpha-hemihydrate (aka gypsum)?

Back 26

refractory (ex: SiO2/silica)

Front 27

What is an example of a refractory in gypsum-bonded investment?

Back 27

Silica (SiO2)

Front 28

What are the three crystalline allotropic forms that silica exists in?

Back 28

quartz, crisobalite, tridymite

Front 29

SiO2 exists in 1 amorphous allotropic form, name this.

Back 29

amorphous silica

Front 30

Which of these forms of crystalline allotropic silica is not often used?

A. Quartz
B. Cristobalite
C. Tridymite

Back 30

C. Tridymite

Front 31

Which of these forms of crystalline allotropic silica causes expansion at low temperatures (200-270C)?

A. Quartz
B. Cristobalite
C. Tridymite

Back 31

B. Cristobalite

Front 32

Which of these forms of crystalline allotropic silica causes rapid expansion between 500-600C?

A. Quartz
B. Cristobalite
C. Tridymite

Back 32

A. Quartz

Front 33

Refractory particle (size/distribution) affects roughness, where (size/distribution) affects density and porosity

Back 33

size, distribution

Front 34

True or False, if the investment has greater particle size (and thus higher roughness) then the casting will be rougher too

Back 34

True

Front 35

What is the purpose of a modifier?

Back 35

-Provide nonoxidizing atmosphere in mold during casting
-regulate setting expansion and setting time, counteract gypsum above 300C
-coloring agent

Front 36

Modifiers are (reducing/oxidizing) agents

Back 36

reducing

Front 37

Modifiers counteract gypsum above ___C

Back 37

300

Front 38

Which component of the investment is colored?

Back 38

modifier

Front 39

C and powdered Cu in modifiers have what effect on the investment?

Back 39

reducing agents that provide a nonoxidizing atmosphere in mold during casting

Front 40

True or False, burnout temperature is jumped from cool to hot very quickly to achieve desirable results

Back 40

False, it is ramped up over time

Front 41

The microstructure of cristobalite reveals (large/small) silica particles, and (cone/rod/spherical) cristobalite particles

Back 41

large, rod

Front 42

What is the setting time range for gypsum-bonded investments?

Back 42

5-25 minutes

Front 43

What is the normal setting expansion % for type 1 gypsum bonded investments in AIR?

Back 43

0.1-0.6%

Front 44

With a lower W/P ratio in gypsum-bonded investments, you get (increased/decreased) exothermic heat which results in a (higher/lower) setting expansion

Back 44

increased, higher

Front 45

If you have thinner pattern walls, you'll have a (higher/lower) setting expansion

Back 45

higher

Front 46

If you use softer inlay wax, you'll have (higher/lower) setting expansion

Back 46

higher

Front 47

Hygroscopic expansion is (greater/less) than normal thermal expansion in air

Back 47

greater

Front 48

Where does setting take place with hygroscopic expansion?

Back 48

water

Front 49

Hygroscopic expansion is greater than or equal to (2/3/4/5/6/7) times more than normal

Back 49

6

Front 50

According to ADA spec. no. 2, hygroscopic setting expansion should be limited to what %?

Back 50

1.2-2.2%

Front 51

What three things might cause expansion in hygroscopic expansion?

Back 51

-crystal interlocking
-hydrostatic pressure in water during setting
-capillary action

Front 52

Finer silica particles leads to (higher/lower) hygroscopic expansion

Back 52

higher

Front 53

In hygroscopic expansion, a higher W/P ratio leads to (higher/lower) setting and thermal expansion

Back 53

lower

Front 54

In hygroscopic expansion, if you immerse before initial set, you'll get (higher/lower) expansion

Back 54

higher

Front 55

In hygroscopic expansion, confinement means you have no ring liner. Does this have a greater or lower effect on expansion?

Back 55

greater

Front 56

The amount of water added is (proportionally/inversely) related with hygroscopic expansion

Back 56

proportional

Front 57

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)

Back 57

D. Aged investment

Front 58

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

Back 58

C. Specimen set while immersed in water

(see chart, page 5.1)

Front 59

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

Back 59

C. Specimen set while immersed in water

(see chart, page 5.1)

Front 60

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

Back 60

A. Specimen set under dry conditions, no wet liner

Front 61

ADA Spec no. 2 limits thermal expansion as follows:

Type 1 - ____ % at ___C
Type 2 - ____ % at ___C

Back 61

Type 1 - 1.0-1.6% at 700C
Type 2 - 0.0-0.6% at 500C

Front 62

True or False, W/P ratio can affect thermal expansion

Back 62

True

Front 63

True or False, it is acceptable to manually or mechanically mix investment material

Back 63

False, always mechanically mix

Front 64

What are three reasons you should mix the investment in a partial vacuum?

Back 64

-Provide better reproduction of surface detail
-Increase the tensile strength of the investment material
-Results in fewer and smaller porosites (voids)

Front 65

For most investment material, shorter mixing time results in (more/less) expansion

Back 65

less

Front 66

What type of investment material is used to cast metal-ceramic alloys that have a high melting range?

Back 66

phosphate-bonded

Front 67

What are the components of the powder in phosphate-bonded investment?

Back 67

90% SiO2 (cristobalite or quartz form),

3% MgO

7% NH4H2PO4

Front 68

What is unique about the liquid in phosphate-bonded investments?

Back 68

You select the percentage of water to silica sol

Front 69

Pure water in phosphate-bonded investments gives you (maximum/minimum) expansion

Back 69

minimum

Front 70

What molecule is released in the setting reaction of phosphate-bonded investments?

Back 70

NH4

Front 71

Phosphate-bonded investments are (more/less) strong and (more/less) rough than gypsum

Back 71

more, more

Front 72

A reaction at higher temperature (increases/decreases) strength and (does/does not) affect surface roughness [in reference to phosphate-bonded investment]

Back 72

increases, does

Front 73

In phosphate-bonded investments, roughness increases as burnout temperature is increased from ___C to ___C

Back 73

1300-1800

Front 74

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

Back 74

silicate-bonded

Front 75

What is the powder composition of silicate-bonded investments?

Back 75

SiO2

MgO

other glasses and refractory oxides in small amounts

Front 76

What are the 4 components of the liquid in silicate-bonded investments?

Back 76

ethyl silicate

denatured ethyl alcohol

stabilized colloidal silica (sometimes)

wetting agent (reduces bubbles on wax)

Front 77

What is the purpose of the wetting agent in silicate bonded investments?

Back 77

to reduce formation of bubbles on wax

Front 78

True or False, air bubbles create nodules on casting that can usually be ground away

Back 78

FALSE, air bubbles do create nodules, but they can't be ground down without doing damage to the casting

Front 79

Green strength is also known as ___ strength

Back 79

wet

Front 80

What does it mean when something has low wet (aka green) strength?

Back 80

The first hour or so it is very weak and prone to cracking. Once it's dry, it's fine.

Front 81

True or False, silicate bonded investments have a low wet/green strength

Back 81

True

Front 82

In silicate bonded investments, vibration of mold causes (bigger/smaller) particles and liquid to rise and makes ring susceptible to cracking by evaporation of ___

Back 82

smaller, alcohol

Front 83

In the setting reaction for silicate bonded investments, the ___ reverts to cristobalite on heating

Back 83

binder (silica gel)

Front 84

In silicate-bonded investments, only thermal (contraction/expansion) occurs

Back 84

expansion