Dental Materials Ii

Front 1

1. What is a metal?

Back 1

Any element that ionizes positively in solution

Front 2

2. What is the crystal lattic structure occupied by gold, palladium, cobalt, nickel?

How is this lattice arranged?

Back 2

Face centered cubic lattice

1. Eight atoms located at the corners of the cube

2. The face centered cell contains an additional atom on each face of the cube

Front 3

3. How do methods to increase strength of metals act?

When do fractures of metals occur?

Back 3

Act by impeding the movement of dislocations

Occurs when the flow of dislocation is blocked and the lattic ruptures

Front 4

4. When will permanent deformation of metals occur?

Back 4

If enough shear (side to side) force is placed on a perfect crystal so that the individual molecules that make ip up begin to slip past one another

Front 5

5. What is an edge dislocation?

Back 5

Defect in crystalline structure that alter the arrangement of other parts of the lattice that radiate away from them

Espcially frequeny in face centered cubic crystalline elements such as gold

Front 6

6. What is a metal alloy?

What are their structures?

Back 6

Mixture of metals

Can have crystal structures like pure metals or other atomic structures such as eutectic or intermetallic compounds

Front 7

7. What does a phase diagram do?


What does a phase diagram show?

Back 7

Describe the nature of alloys and metal solubilities

Maps of the phases that occur when metals are mixed together

The composition and types of phases at a given temperature

**divide alloy into at least three areas: liquid phase, liquid-solid phase, and solid phase

Front 8

8. What is the area below the solidus line?

What is the are above the liquidus line?

Back 8

All solid

All liquid

Front 9

9. What are the three possible outcomes when metals are mixed in a molten state, then cooled to a solid state?

Back 9

1. Solid solution
-metals remain soluble in one another

2. Eutectic is formed
-metals not soluble in solid state

3. Intermetallic compound
-elements may react

Front 10

10. What is nucleation?

What happens as cooling continues?

Back 10

A process where the first solid alloy particles form when the temperature reaches the liquidus

Nuclei grow into crystals (grains) which enlarge until the boundaries of the grains meet

Front 11

11. What is the current system for classifying dental alloys based upon?

Back 11

1. Physical properties

2. Composition

Front 12

12. How are dental alloys classified based on composition?

Back 12

1. High noble

2. Noble

3. Primarily base metal

Front 13

13. Describe high nobles

Back 13

-gold content > 40 wt%
-noble metal content > 60 wt%

-usually contain small amounts of tin, idium, and/or iron for oxide layer formation

**increases alloy’s bond strength to porcelain by factor of three

**most commonly used one is type III

Front 14

14. What are the disadvantages of high nobles?

What are the subclasses of high noble alloys?

Back 14

disadvantages:
1. Lower rigidity
2. Poor sag resistance

subclasses of high noble alloys

1. Gold – platinum
2. Gold – palladium
3. Gold – copper – silver – palladium

Front 15

15. What are gold-platinum alloys used for?

What is there composition?

Back 15

Used for full cast and metal-ceramic restorations and short span fixed partial dentures

Have silver or zinc as hardeners

Composition:
1. Gold – 85%
2. Platinum – 12%
3. Zinc – 1%

Front 16

16. What are gold-palldium alloys used for?

What are their compositions?

Back 16

Full cast or metal-ceramic restorations

1. Gold - 52%

2. Palladium - 38%

3. Indium - 8.5%

**promote oxide layer for better bonding to porcelain

Front 17

17. What are the four subclasses of noble metals?

Back 17

1. Gold-copper-silver-palladium
-similar composition to high noble gold-copper-silver-palladium alloys but less gold content

2. Gold-silver-palladium-indium

3. Palladium-copper-gallium

4. Palladium-silver and Silver-palladium

Front 18

18. What does gallium do in a metal alloy?

Back 18

Lowers melting temperature so improve castability

**enhance bonding of porcelain to metal and increase strength

Front 19

19. What do high silver alloys exhibit more of?

What can silver do to porcelain?

Back 19

Exhibit more corrosion

Silver can cause greening of porcelain

Front 20

20. What are the physical properties of primarily base-metal alloys?

Back 20

Melting temperature:

1. "High heat" cobalt
-chromium alloys melt above 1300 C

2. "Low heat" nickel
-chromium alloys melt in range of 1140 to 1250 C

Front 21

21. What are the chemical properities of primarily base metal alloys?

Back 21

1. Good electrochemical corrosion

2. Chromium inhibits corrosion (can still get pitting if rough surface)

3. All chromium type alloys are attacked by chlorine

Front 22

22. What happens during nucleation?

What can the addition of grain refiners cause?

How does grain formation occur?

Back 22

Molten metal alloy is cooled and the first solid alloy particles form as temperature reaches liquidus

Fine particles (such as Ir) encourage uniform nucleation throughout the alloy

Crystals formed from growing nuclei as the cooling continues and the grains enlarge until all of the liquid is gone

Front 23

23. What are grain boundaries?

What does grain size depend on?

(three things)

Back 23

Boundaries formed between grains when they meet that often contain impurities

1. Cooling rate
-slow = few impurities/large grains
-fast = smaller grains

2. Alloy composition

3. Presence of grain refiners
-smaller grains

Front 24

24. What is columnar grain growth?

Back 24

Mass of molten metal is cast into cold mold

Grains from and grow from walls of the mold to the center of the mass

**leads to alloy weakness from interference boundaries

Front 25

25. What are the six families of lattices?

Back 25

1. Cubic
(simple, body-centered, face-centered)
2. Triclinic
3. Tetragonal
(simple, BC, FC)
4. Orthorhombic
(simple, BC, FC, base-centered)
5. Hexagonal
6. Monoclinic
(simple, base-centered)

Front 26

26. What are the most common lattices in dental alloys?

Back 26

1. Body-centered cubic
-all atoms equidistant
-atoms at corner of unit cell and one atom is in center

2. Face-centered cubic
-atomic centers equidistant
-atoms in centers of faces w/ no atoms in center of unit cell

3. Hexagonal

Front 27

27. What is the crystal lattice structure occupied by gold and other noble and non-noble dental alloys?

Back 27

Face-centered cubic
-gold
-palladium
-cobalt
-nickel

Front 28

28. What is an ordered solution?

How can you obtain a random arrangement solid solution?

How can you obtain an ordered solution?

Back 28

When two elements in the alloy assume regular and specific positions in the crystal lattice of the alloy

Rapid cooling below solidus line

Need heat treatment

Front 29

29. What is a phase diagram?

Back 29

Shows the composition and types of phases at a given temperature and at equilibrium

X-axis is composition

Y-axis is temperature

Front 30

30. Why is the liquidus line a phase diagram important?

How do you know if it is a solid solution in a phase diagram?

How do you know if it is an ordered solution in a phase diagram?

How is a second phase indicated on a phase diagram?

Back 30

Tells burnout temp which is 500 C below the liquidus line

**want a narrow difference bwt liquidus and solidus line

Area below the solidus line contains no boundaries

Area below the solidus line contains dashed lines

Indicated by an area below the solidus line which contains a solid line

Front 31

31. What are the elements classified as noble?

seven....

Back 31

1. Gold
2. Platinum
3. Palladium
4. Iridium
5. Rhodium
6. Ruthenium
7. Osmium

**metal that is resistant to oxidation

Front 32

32. What does platinum do in gold-based alloys?

Back 32

1. Raises melting temperature
2. Increases tensile strength
3. Decreases coefficient of thermal expansion
4. Reduces tarnish and corrosion

Front 33

33. What does palladium do in gold-based alloys?

Back 33

1. Raises melting temperature
2. Increases hardness
3. Acts to absorb H gas
(can cause porosity in casting)
4. Prevent tarnish and corrosion
5. Strong whitening effect when used in low concentrations

Front 34

34. Which elements contribute to the hardening of dental gold?

Back 34

1. Copper
*principal hardener and needed for heat treatment

2. Palladium

3. Indium (to much lesser degree)

4. Platinum

5. Silver

Front 35

35. Which metal elements contribute to elevating the melting point of gold dental alloys?

Which three elements are added to fractional amounts to harden high-gold content alloys to be used w/ porcelain?

Back 35

1. Platinum
2. Palladium

1. Iron
2. Tin
3. Indium

Front 36

36. What do precious metal casting alloys contain?

Back 36

1. Gold

2. Palladium

3. Platinum

4. Silver

Front 37

37. How do the following effect dental casting alloys....

1. Gold
2. Copper
3. Silver

Back 37

1. Gold
-increases resistance to tarnish and corrosion
-increases ductility and malleability

2. Copper
-principal hardener
-necessary for heat treatment

3. Silver
-modify red color produced by gold and copper
-reduce melting temperature
-increase ductility and malleability

Front 38

38. How do the following effect dental casting alloys....

4. Silver
5. Palladium

Back 38

4. Platinum
-raises melting temperature
-increases tensile strength
-decreases coefficient of thermal expansion
-reduces tarnish and corrosion

5. Palladium
-raises melting temperature
-increases hardness
-absorbs H gas (which can cause porosity in casting)
-prevents tarnish and corrosion
-strong whitening effect on gold alloys

Front 39

39. How do the following effect dental casting alloys...

6. Zinc
7. Idium

Back 39

6. Zinc
-prevents oxidation of other metals
-increases fluidity and decreases surface tension (improves castability)

7. Idium
-grain refiner
-increases tensile strength and percent elongation (i.e. ductility)

Front 40

40. Which elements contribute to grain refinement?

What is the concept of grain refinement?

Which elements enhance the oxide layer on PFM alloys?

Back 40

Iridium

Smaller grains give stronger, more ductile and homogenous casting

1. Indium
2. Tin
3. Iron

**tin and iron are hardeners in PFM alloys

Front 41

41. What effect doe palladium content have on the color of gold alloys?

Back 41

Gives white color in low concentrations

Front 42

42. What are the properties of an ideal noble casting alloy?

Back 42

1. Low melting range
2. Narrow solidus-liquidus temp range
3. Adequate strength, hardness, and elongation
4. Good corrosion resistance in oral cavity
5. Low cost

**Gold and palladium are preferred

Front 43

43. What is nickel-chromium alloy?

Back 43

Base metal alloy

Nickle - 70%
Chromium - 16%
Minor - aluminum and beryllium

**aluminum and nickle for intermetallic compound (strength and hardnes)

Front 44

44. What are the properties of noble metal alloys?

Back 44

1. Very rigid

Palladium-silver and Silver-palladium

1. Low sag tendency
2. High rigidity
3. Easy to solder

Front 45

45. What is the current system for classifying dental alloys based upon?

What is the physical property system for classifying dental alloys according to the ADA?

Back 45

1. Physical properties
2. Composition

Type I
Type II
Type III
Type IV

Front 46

46. Describe Type I

Describe Type II

Back 46

Type I
-soft
- yield strength < 140 MPa
-18% elongation
-VHN: 60 to 90
-inlay

Type II
-medium hardness
-yield strength 140 to 200 MPa
-18% elongation
-VHN 90 to 120
-inlay, onlay

Front 47

47. Describe Type III

Describe Type IV

Back 47

Type III
-hard
-201 to 340 MPa
-12%
VHN: 120 to 150

Type IV
-extra hard
>340 MPa
10%

Front 48

48. What are the intended uses of the ADA type I, II, III and IV?

Back 48

Type I
-one surface restorations subjected to slight stress (in lays)

Type II
-two or three surface inlays (stress bearing areas)

Type III
-crowns and fixed bridge work
-short span FPD

Type IV
-partial dentures

Front 49

49. What does chromium confer to base metal alloys?

Back 49

Tarnish and corrosion resistivity

Front 50

50. What is melting range important to dental casting alloys?

Back 50

Important in selection of casting equipment, investment, and control of casting

Base metal alloys differ from gold casting alloys

Base: 1150 to 1500 C
Gold: 80 to 1050 C

**1-2% beryllium lowers melting temp of Ni-Cr

Front 51

51. Why is density important in dental casting alloys?

Back 51

Important in bulky maxillary appliances

Force of gravity causes relative wieght of casting to place additional forces on supporting teeth

Reduce weight -> lower density of cast base metal alloy

Front 52

52. What does yield strength indicate?

What is it important for?

What must dental alloys have a yield strength of?

Back 52

Indication when permanent derformation of device or part of device occurs

RPD

415 MPa

Front 53

53. What does percent elongation indicate?

Why is it important for RPD?

What increases ductility and elongation?

Back 53

Relative brittleness or ductility in restoration

Partial denture clasp need high elongation and tensile strength so it doesn't fracture

Increase Ni w/ reduction in Co

Front 54

54. How does cast base metal alloys hardness compare w/ gold alloys?

What is a homogenizing (softening) heat treatment?

Back 54

Hardness is 1/3 greater than gold alloys

Heat to approx 75 degrees C below solidus temp then hold for 10 to 30 minutes (get better ductility)

**quench w/ water for softening

Front 55

55. What are two common ways of strengthening noble dental alloys?

How can hardening of precious metal casing alloys be accomplished?

Back 55

1. Solid solution hardening

2. Order solution hardening

1. Slow cooling
2. Constant temperature heath treatment

Front 56

56. How does the formation of an ordered solution affect gold based casting alloys?

Back 56

1. Increase yield strength (50%)

2. Increase tensile strength (25%)

3. Increase hardness (10%)

4. Reduce elongation

Front 57

57. Describe a hardening treatment.

Back 57

Heat for 10 minutes at 350 C followed by water quenching or rapid cooling in air

Cooling a casting in a mold to room temp (bench warming) will produce hardening

Front 58

58. What five elements are usually present in white gold alloys used w/ porcelain?

Back 58

1. Palladium

2. Silver

3. Gold

4. Tin

5. Indium

Front 59

59. What is ordering in the gold-copper system?

Back 59

Ordering is a crystal structure organization in which the atoms of an element are regularly arranged in a repeating pattern as opposed to a random distribution

Front 60

60. Which mechanical property is usually considered a measure of burnishability of a soft inlay alloy?

Back 60

Ductility or percent elongation

Measure the degree to which the alloy can be burnished (spread)

**hardness and yield strength indicate a resistance to burnishing

Front 61

61. What is the process of cold-working?

Back 61

Metal is cast into ingots

Subjected to rolling, swaging, or wire drawing to produce several mechanical deformation

Finished product is a wrought structure

Front 62

62. How are the mechanical properties of wrought structures?

What happens to the grains when a metal is subjected to cold-working operations?

Back 62

Superior to those of a casting prepared from same melt or alloy

1. Broken down
2. Entangled in each other
3. Elongated

**cold working strengthens and embrittles (less ductile) alloy

Front 63

63. How do nonprecious alloys compare w/ precious metal alloys?

Back 63

Non-precious
-lower cost
-higher hardness, tensile strength, elastic modulus
-elongation is about same as precious

Front 64

64. What is soldering?

What are the two types of (hard) solder?

Back 64

Two pieces of metal are joined by a third piece of metal at a temperature below 425 degrees C

1. Gold-based
-crown and bridge application
2. Silver-based
-orthodontic appliances

Front 65

65. What is the basic classification of solders?

Back 65

1. Soft
-lead tin alloys of eutectic type w/ low melting point

2. Hard
-have a higher melting temperature and posses greater hardness and strength

Front 66

66. What are the components of gold based solders?

What is the composition of most gold solders?

Back 66

Primarily alloys of gold, silver, and copper

Small amounts of tin, zinc, and phosphorus

Copper/gold ratio to support formation of Au-Cu ordered phase

**fusion temp is lower for alloys that have reduced gold content

Front 67

67. What is meant by "easy-flowing" and "free-flowing" qualities of dental solders?

Back 67

Easy-flowing
-solder that has a relatively low fusion temperature
(easier to melt and form a joint)

Free-flowing
-ability of solder to spread and flow freely over the surfaces of the parts being joined
(closely related to surface tension)

Front 68

68. What is the minimum difference in the fusion temperature bwt the dental solder and the parts being joined?

Back 68

Fusion temp of solder must be below that of alloys being solder or joined pieces will melt during process

Should be at least 56 C below that of parts being joined to prevent distortion

Front 69

69. What are the six properties of an ideal solder?

Back 69

1. Ease of flow at relatively low temp
2. Sufficiently fluidity to freely flow when melted
3. Strength compatible w/ that of structure being soldered
4. Acceptable color to give inconspicuous joint
5. Resistance to tarnish and corrosion
6. Resistance to pitting during heating

Front 70

70. How can pitting of solder joints occur?

How is a well formed solder joint?

Back 70

1. Overheating
(pits and loss of strength)

2. Under heating
(pitting and failure of solder to flow and cause adhesion)

1. Kept away from margins and occlusal grooves (use antiflux material)
2. Few hundrethes of millimeter bwt parts to be joined

**intimate: pieces will expand and push apart on heating
**too much distance: parts draw together

Front 71

71. What are the basic properties of silver based solders?

Back 71

1. Low melting range
2. Higher corrosion rate
3. Lowered resistance to tarnish than gold based solders
4. Comparable strength to gold based solders

Commonly used for ortho wires

Front 72

72. What are the two soldering methods?

Back 72

1. Free-hand

2. Investment soldering