Material Science of Metal-Ceramics

Question 1

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

Answer 1

Mechanical

Question 2

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

Answer 2

Modulus of elasticity

Question 3

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

Answer 3

Elongation

Question 4

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

Answer 4

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

Question 5

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

Answer 5

Fracture

Question 6

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

Answer 6

Physical

Question 7

Translucency and color are also known as ______ properties.

Answer 7

Optical

Question 8

What does LCTE stand for?

Answer 8

Linear Coefficient of Thermal Expansion

Question 9

Which has a higher UTS, enamel or dentin?

Answer 9

Dentin (UTS = ultimate tensile strength)

Question 10

Which has a greater VHN, enamel or dentin?

Answer 10

Enamel (hardness)

Question 11

Metals are strong and ________.

Answer 11

Ductile

Question 12

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

Answer 12

Dislocations

Question 13

What is the axial reduction requirement for MCC preparations?

Answer 13

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

Question 14

Noble metals will resist _______, tarnish, and corrosion.

Answer 14

oxidation

Question 15

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

Answer 15

Pure metals are too soft

Question 16

What methods can be employed to improve alloy mechanical properties?

Answer 16

1. Solid Solution Hardening

2. Grain Refining

Question 17

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

Answer 17

To resist deformation and to impede dislocations

Question 18

What is solid solution hardening?

Answer 18

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.

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

Grain refining will have what benefits on noble metals?

Answer 21

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

Question 22

What are the three casting alloys present in noble metals?

Answer 22

Au, Pd, and Pt

Question 23

How do casting alloys effect noble metals?

Answer 23

Increase hardness

Question 24

Into how many categories are casting alloys classified?

Answer 24

four

Question 25

What are the four classifications of casting alloys?

Answer 25

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

Question 26

Strength of alloys is determine by ______ Hardness Test.

Answer 26

Vicker's

Question 27

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

Answer 27

>80

Question 28

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

Answer 28

>40

Question 29

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

Answer 29

False: 25% noble metal but NO GOLD REQUIREMENT

Question 30

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

Answer 30

25

Question 31

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

Answer 31

CVC (partial veneer crowns or onlays), not mcc

Question 32

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

Answer 32

Type III

Question 33

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

Answer 33

True. 25% noble metal without a gold requirement percentage

Question 34

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

Answer 34

Gold and Pd

Question 35

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

Answer 35

0.01% Ir (always Ir or Ru)

Question 36

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

Answer 36

Yellow | Full Cast Crown and Bridge

Question 37

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

Answer 37

Alloys are oxidation resistant

Question 38

What is "Super Star"?

Answer 38

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

Question 39

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

Answer 39

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

Question 40

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

Answer 40

Ru | midas contains Ir

Question 41

Which elements in Super Star produce solid solution hardening?

Answer 41

Au, Ag, and Pd

Question 42

What is enamel's Vicker's Hardness rating?

Answer 42

~350 kg/mm^2

Question 43

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

Answer 43

UTS (tensile strength) | VHN (hardness)

Question 44

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

Answer 44

Enamel (yes) Dentin Metal (not translucent)

Question 45

What are the three components of Dental Porcelain?

Answer 45

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

Question 46

What kind of bonds are associated with ceramics?

Answer 46

Ionic and Covalent

Question 47

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

Answer 47

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

Question 48

Which type of bond requires an equal sharing of electrons?

Answer 48

Covalent

Question 49

What is the building block of Dental Porcelain?

Answer 49

SiO4 tetrahedron

Question 50

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

Answer 50

Quartz (or crystobilite) | Leucite

Question 51

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

Answer 51

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

Question 52

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

Answer 52

Ceramics: brittle Metal: ductile Plastic: ductile

Question 53

Ceramics are weak in ______ forces.

Answer 53

Tension

Question 54

Brittle fractures in ceramic is initiated from the ______ surface.

Answer 54

Internal

Question 55

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

Answer 55

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

Question 56

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

Answer 56

Griffith's | tensile

Question 57

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

Answer 57

Compressive | Insulator

Question 58

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

Answer 58

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

Question 59

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

Answer 59

LOWER the melting temperature | do not want the metal to melt in processing

Question 60

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

Answer 60

Compressive | Its "okay" because ceramics have high CS

Question 61

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

Answer 61

Tension | this is bad because porcelain has poor TS

Question 62

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

Answer 62

metal -oxide layer | silicon oxygen

Question 63

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

Answer 63

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