Dental Materials II

Question 1

Stress/Strain curve for:
Stiff
Ductile
Strong
Tough

Answer 1

2;30

Question 2

Stress/Strain curve for:
Flexible
Brittle
Weak

Answer 2

2;30

Question 3

How does rapid cooling affect the atomic structure of metals and alloys?

Answer 3

Forms more nuclei per unit volume

Decreases grain size

Question 4

What 2 terms are used for the ability of atomic centers to slide against each other into new positions within the same crystal lattice?

Answer 4

Ductility

Malleability

Question 5

For metals and alloys, what raises yield strength, increases ductility, and raises the ultimate strength?

Answer 5

Finer grain size

Question 6

What is related to plastic deformation and fracture in metals and alloys?

Answer 6

Change grain size

Question 7

A fracture due to a crack opening up on a grain boundary is more likely to occur in…

Answer 7

Large grain metals

Question 8

The mechanism of plastic deformation is called…

Answer 8

Dislocation motion

Question 9

What process causes many plastic deformations by producing dislocations (and increases likelihood of fracture)?

Answer 9

Cold Working (wrought)

Question 10

The phase diagram of metals and alloys reveals…

Answer 10

Melting range

Question 11

What are the 3 possibilities when mixed metals are cooled?

Answer 11

Solid Solution - (soluble)
Eutectic - (not soluble)
Intermetallic compound (rxn)

Question 12

What 2 metals always form a solid solution?

Why?

Answer 12

Au and Cu

Soluble

Question 13

What is special about ordered solutions?

Answer 13

They impart greater hardness

Question 14

When Au and Cu occupy specific positions, it is an…

Answer 14

ordered solution

Question 15

When 2 metals are soluble as liquids, but nearly insoluble as solids, they form…

Answer 15

Eutectic alloys

Question 16

A pure Eutectic has a ______ that is ______ than either of the pure components.

Answer 16

Melting point (not range)
Lower

Question 17

What % by weight must a noble alloy contain to be considered noble?

Answer 17

25%

Question 18

Carat content of pure gold:

Answer 18

24 K

Question 19

How is fineness measured?

Answer 19

out of 1000

75% pure = 750

Question 20

What 2 effects will adding 10% Cu to Au have?

Answer 20

Increase tensile strength
Increase BHN

(what is BHN?)

Question 21

What 2 factors does the creation of an ordered solution depend on?

Answer 21

% metals

Cooling rate

Question 22

T/F

An ordered solution will increase hardness, decrease elongation, and increase yield strength.

Answer 22

True

Question 23

T/F

The stress at any point in a Ceramic is the same as the average stress

Answer 23

True

*if stretched

Question 24

In ceramics, where will stress rise significantly?

Answer 24

around a Stress Raiser

*groove and edge of groove

Question 25

What allows water molecules to penetrate polymer chains?

Answer 25

Weak secondary bonds

Question 26

What defines high noble? Noble? Base metal?

Answer 26

60% noble / 40% gold 25% noble less than 25%

Question 27

What adds color to ceramics?

Answer 27

Metallic Oxides

Question 28

What are the 2 post-manufacture phases of feldspathic dental porcelain?

Answer 28

Vitreous (glass) | Crystalline (mineral/leucite)

Question 29

The Vitreous phase of ceramic porcelain is like...

Answer 29

Glass

Question 30

The Crystalline phase of ceramic porcelain contributes what 2 things?

Answer 30

``` Strength Thermal Expansion (high) ```

Question 31

What process joins porcelain particles together?

Answer 31

Sintering *Biscuit Bake

Question 32

What often fractures in the Oxide layer of ceramics-metal bonds?

Answer 32

Base metals *layer too thick

Question 33

Where does the fracture take place if proper bonding occurs in ceramic-metal specimens?

Answer 33

Porcelain

Question 34

In a ceramic-metal system, the Coeffecient of Thermal Expansion must be ____ for the metal.

Answer 34

Higher *puts ceramic into compression where it is stronger

Question 35

What type of wax will soften when heated?

Answer 35

Thermoplastic

Question 36

T/F | Waxes have a low degree of thermal expansion.

Answer 36

False

Question 37

What type of stress in waxes usually results from non-uniform heating/cooling? How can this be relieved?

Answer 37

Internal Release Residual stress by heating

Question 38

4 characteristics of all Waxes:

Answer 38

Melting range Tendency to flow Residual Stresses Largest CTE of all dental matls

Question 39

What is the most accurate way to dispense the mixing powder making up aliginate impression materials?

Answer 39

Weighing

Question 40

What ingredient in Alignate retards hardening?

Answer 40

Sodium phosphate aka tri-sodium phosphate

Question 41

What can cause the shrinkage and distortion of an aliginate impression due to fluid loss? (not evaporation)

Answer 41

Syneresis

Question 42

T/F | Syneresis is the same as evaporation

Answer 42

False

Question 43

What can cause expansion of an Aliginate impression?

Answer 43

Imbibition

Question 44

What is Imbibition?

Answer 44

The uptake of water in the gel state

Question 45

What can lead to shrinkage of an Aliginate impression and is often due to level of humidity in the room?

Answer 45

Evaporation

Question 46

What is the basis for all gypsum used in dentistry?

Answer 46

Calcium sulfate hemihydrate

Question 47

The 3 types of material derived from the partial dehydration of gypsum rock (plaster, stone, high strength stone) have what major difference?

Answer 47

Manner of driving off water

Question 48

What 3 materials are derived from Mineral Gypsum (dihydrate)?

Answer 48

Plaster Dental stone High strength stone

Question 49

The gypsum setting reaction is what type? characterized by what 3 things?

Answer 49

Nucleated recrystallization continuous solution of hemihydrate diffusion of Ca and sulfate ions to nucleation centers Precipitation of microscopic gypsum crystals

Question 50

What leads to less porosity and more strength in gypsum products?

Answer 50

Less water

Question 51

What leads to more porosity and less strength in gypsum products?

Answer 51

More water

Question 52

Why do thick mixes in water/powder of gypsum products harden more quickly?

Answer 52

Nucleation centers concentrated

Question 53

T/F | Porosity tends to strengthen gypsum products

Answer 53

False

Question 54

What happens if you decrease the water/powder ratio in a gypsum product?

Answer 54

Denser cast

Question 55

What does increasing the Water/Powder ratio do to gypsum products?

Answer 55

Decrease Strength

Question 56

How is Gypsum used in gold alloy casting?

Answer 56

as a Binder

Question 57

What provides expansion to compensate for gold shrinkage?

Answer 57

Refractory | a silicone dioxide

Question 58

What are the 2 functions of Binder in Gypsum Bonded Investments?

Answer 58

Forms solid mass | Provides strength

Question 59

What is the composition of Binder in Gypsum Bonded Investments for gold? For high temp alloys?

Answer 59

Calcium sulfate hemihydrtate Phosphate, ethyl silicate

Question 60

What is the low temperature phase for a silica? | High temperature phase?

Answer 60

Alpha Beta *change between 2 is responsible for most thermal expansion

Question 61

T/F | A Utectic has a melting range and not a melting point

Answer 61

False *Has a Melting Point

Question 62

What is the difference between a Thermoplastic and Thermoset material?

Answer 62

Thermoplastic - Softens upon heating | Thermoset - no expansion/contraction on heating stronger

Question 63

What gives polymers its properties?

Answer 63

Molecular weights of make-up

Question 64

What is responsible for the Thermal Expansion of porcelain?

Answer 64

Leucite phase

Question 65

What does a refractory component do?

Answer 65

controls expansion

Question 66

Does the refractory material have strength? | What holds it together?

Answer 66

No | Gypsum binder

Question 67

T/F | Metal should have slightly higher coefficient of thermal expansion than porcelain

Answer 67

True