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Fixed 2- Summer 2015 > Material Science of Metal-Ceramics > Flashcards

Material Science of Metal-Ceramics Flashcards

1
Q

Ultimate strength, yield strength, modulus of elasticity, elongation, and hardness are ______ properties of dental materials.

A

Mechanical

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2
Q

The slope of a stress-strain curve indicates which mechanical property?

A

Modulus of elasticity

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3
Q

The end of the elastic stage, just before fracture, is indicative of which mechanical property?

A

Elongation

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4
Q

An increase in the modulus of elasticity (slope) will ______ stiffness.

A

Increase (stress is Y-axis, strain is X-axis)

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5
Q

What will occur when reaching the point of ultimate tensile strength?

A

Fracture

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6
Q

Density, LCTE, Electrical character, translucency, color, and wetting are _______ properties of dental materials.

A

Physical

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7
Q

Translucency and color are also known as ______ properties.

A

Optical

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8
Q

What does LCTE stand for?

A

Linear Coefficient of Thermal Expansion

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9
Q

Which has a higher UTS, enamel or dentin?

A

Dentin (UTS = ultimate tensile strength)

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10
Q

Which has a greater VHN, enamel or dentin?

A

Enamel (hardness)

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11
Q

Metals are strong and ________.

A

Ductile

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12
Q

Within the micro-structure of materials, slips occur at ________.

A

Dislocations

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13
Q

What is the axial reduction requirement for MCC preparations?

A

1.5 mm where esthetics are needed (0.3 mm metal+ 0.2mm opaque+ 1.0 mm porcelain)

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14
Q

Noble metals will resist _______, tarnish, and corrosion.

A

oxidation

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15
Q

Why are alloys used for cast metal and metal-ceramic restorations instead of pure metal?

A

Pure metals are too soft

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16
Q

What methods can be employed to improve alloy mechanical properties?

A
  1. Solid Solution Hardening

2. Grain Refining

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17
Q

For what purpose are noble metals strengthened through Solid Solution Hardening?

A

To resist deformation and to impede dislocations

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18
Q

What is solid solution hardening?

A

adding atoms of one element (the alloying element) to the crystalline lattice of another element (the base metal). The alloying element diffuses into the matrix, forming a solid solution.

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19
Q

How is “grain formation” used to strengthen noble metals?

A

Grain boundaries in metal will RESIST deformation. Therefore, making grains smaller and increasing the number of grain boundaries will lead to decreased deformation

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20
Q

What is the difference between grain “formation” and grain “refining” when strengthening noble metals?

A

Grain formation: increasing number of boundaries by forming grains from the molten metal
Grain Refining: decreasing grain size

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21
Q

Grain refining will have what benefits on noble metals?

A

Very fine grains = more boundaries (block dislocations), increased tensile strength, improved elongation, increased ductility and hardness

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22
Q

What are the three casting alloys present in noble metals?

A

Au, Pd, and Pt

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23
Q

How do casting alloys effect noble metals?

A

Increase hardness

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24
Q

Into how many categories are casting alloys classified?

A

four

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25
Q

What are the four classifications of casting alloys?

A

Type I: Soft (59-90)
Type II: Medium (90-120)
Type III: Hard (120-150)
Type IV: Extra Hard (>150)

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26
Q

Strength of alloys is determine by ______ Hardness Test.

A

Vicker’s

27
Q

A casting alloy that is classified as having a “very high” noble metal content would have ____% gold.

A

> 80

28
Q

A casting alloy that is classified as having a “high” noble metal content would have _____% gold.

A

> 40

29
Q

True or False: A casting alloy that is classified as “noble metal” must be 25% gold.

A

False: 25% noble metal but NO GOLD REQUIREMENT

30
Q

A casting alloy that is considered “predominantly base metal” would contain less than ____% noble metal.

A

25

31
Q

The “Midas” product used in OSU Clinics is a material that is used for _____ NOT ______.

A

CVC (partial veneer crowns or onlays), not mcc

32
Q

Midas is classified as Type____ based on Vickers Hardness, meaning its strength is 120-150.

A

Type III

33
Q

True or False: Midas is a Noble Metal Alloy meaning that it contains 25% noble metal.

A

True. 25% noble metal without a gold requirement percentage

34
Q

Which elements are present in Midas that act as a Solid Solution Hardener?

A

Gold and Pd

35
Q

Which element is present in Midas to produce more refined grains?

A

0.01% Ir (always Ir or Ru)

36
Q

Argenco Y+ is a Type III noble metal alloy that is _____ in color and is used for ________.

A

Yellow

Full Cast Crown and Bridge

37
Q

Why do alloys have improved metal-ceramic bonding when compared to pure metals?

A

Alloys are oxidation resistant

38
Q

What is “Super Star”?

A

It is a Type IV alloy (>150 hardness)
used for MCC
White appearance

39
Q

Why is Super Star used for MCC but Midas cannot be used for MCC?

A

Super-Star contains tin with allows for Metal-Ceramic bonding

40
Q

What is the grain refiner that is present in Super Star?

A

Ru

midas contains Ir

41
Q

Which elements in Super Star produce solid solution hardening?

A

Au, Ag, and Pd

42
Q

What is enamel’s Vicker’s Hardness rating?

A

~350 kg/mm^2

43
Q

Dentin has a higher _____, whereas enamel has a higher ____ (mechanical properties).

A

UTS (tensile strength)

VHN (hardness)

44
Q

Rank enamel, dentin, and metals from highest to lowest translucency.

A

Enamel (yes)
Dentin
Metal (not translucent)

45
Q

What are the three components of Dental Porcelain?

A

70-80% Potash feldspar
10-30% Quartz….for the matrix
0-3% Kaolin (clay)….for the workability

46
Q

What kind of bonds are associated with ceramics?

A

Ionic and Covalent

47
Q

Rank ionic, metallic, and covalent bonds from highest to lowest strength.

A

(most) –Covalent, Ionic, Metallic– (least)

48
Q

Which type of bond requires an equal sharing of electrons?

A

Covalent

49
Q

What is the building block of Dental Porcelain?

A

SiO4 tetrahedron

50
Q

Dental Porcelain contains noncrystalline silicate-glass and crystalline silicates ____ and _____.

A

Quartz (or crystobilite)

Leucite

51
Q

True or False: Ceramics have bad optical properties because increased crystals decrease the translucency.

A

False: Ceramics have good optical properties EVEN THOUGH increased crystals will decrease translucency

52
Q

Ceramics are stiff and _______; metals are stiff and ______; plastics are flexible and ______.

A

Ceramics: brittle
Metal: ductile
Plastic: ductile

53
Q

Ceramics are weak in ______ forces.

A

Tension

54
Q

Brittle fractures in ceramic is initiated from the ______ surface.

A

Internal

55
Q

True or False: Fracture in dental ceramic will begin at the external surface due to cyclic fatigue.

A

False: Begins at INTERNAL due to cyclic fatigue and stress corrosion

56
Q

_____ Flaws in ceramics are due to brittle fracture (atoms unable to deform) and low ____ strength.

A

Griffith’s

tensile

57
Q

Ceramics have high ______ strength and act as a thermal/electrical ______.

A

Compressive

Insulator

58
Q

What are the three requirements in order for porcelain to bond to metal?

A
  1. Porcelain must have a lower melting temp. than metal
  2. Porcelain must have a similar COTE to the metal
  3. Porcelain must wet the surface of the metal
59
Q

The silica-glass of porcelain is modified with Na, K, Ca, and F in order to break up the matrix so as to ______.

A

LOWER the melting temperature

do not want the metal to melt in processing

60
Q

If the metal shrinks/expands more than the ceramic during heating or cooling, _____ forces will be put on the ceramic. Is this bad?

A

Compressive

Its “okay” because ceramics have high CS

61
Q

If the ceramic shrinks/expands more than the metal during heating or cooling, ______ forces will be put on the ceramic. Is this bad?

A

Tension

this is bad because porcelain has poor TS

62
Q

“Wetting the Surface of Metal” refers to the creation of a _____ layer between the metal and glass by way of which element?

A

metal -oxide layer

silicon oxygen

63
Q

Which element determines whether a material can be used for an MCC?

A

Sn (tin!…which is present in SuperStar and not Midas)

Fixed 2- Summer 2015 (7 decks)

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