Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BDS M5 Dental Materials > Base metal casting alloys > Flashcards

Base metal casting alloys Flashcards

1
Q

What do base metal casting alloys NOT contain?

A

no Au, Ag, Pt or Pd

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

In dentistry what do base metal casting alloys comprise of?

A
  1. Co/Cr
  2. Ni/Cr
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is Co/Cr mainly used for?

A

mainly partial denture frameworks and complete denture bases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does Ni/Cr have applications in?

A

crown and bridge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the constituents of Co/Cr?

A
  • cobalt
  • chromium (no less than 25%)
  • molybdenum (no less than 4%)
  • cobalt + nickel + chromium (no less than 85%)
  • plus traces of elements Be, Si and C
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the actions of the cobalt and nickel constituents of Co/Cr?

A

confer hardness and strength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the actions of the chromium constituent of Co/Cr?

A

hardness and corrosion resistance (passivating effect)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does the passivating effect of chromium mean?

A

interaction of chromium and oxygen —> chromium oxide which is fairly resistant to corrosion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the actions of the trace inclusion constituents of Co/Cr?

A

improve casting and handling

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the constituents of Ni/Cr?

A
  • nickel (main constituent)
  • chromium (no less than 20 %)
  • molybdenum (no less than 4 %)
  • beryllium (no less than 2 %)
  • nickel + Cobalt + Chromium (no less than 85 %)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What constituent is there concern about being contained in dental alloys?

A

beryllium - carcinogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the fusion temperature for base casting alloys Co/Cr and Ni/Cr?

A

1200-1500 degrees C
- higher than gold alloys

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How are fusion temperatures for Co/Cr and Ni/Cr achieved?

A

either electrical induction or any acetylene torch

(1200-1500 degrees C)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the density of Co/Cr and Ni/Cr compared to gold alloys?

A

lower density than gold alloys

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Why does the casting machine for Co/Cr and Ni/Cr need to be different to that for gold alloys?

A

Co/Cr and Ni/Cr lower density
- need to avoid miscasting by having :
- additional casting thrust
- porous investment material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How are Co/Cr and Ni/Cr finished?

A

time consuming to finish
- sandblasting possible
- for Co/Cr alone electrolytic polishing

  • wary of finishing heat gain if fused to porcelain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are steel and stainless steel most widely used as?

A

wrought alloys
- instruments, burs and wires, and sometimes denture bases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What can be done to steel and stainless steel shape it?

A

hammered, drawn or bent into shape at temperatures well below the metal recrystallisation temperature
- may lead to work hardening (advantage/disadvantage)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the pros and cons of work hardening of steel and stainless steel?

A

pro: toughens up the alloy
con: if over work hardened more predisposed to fracture

20
Q

What is steel?

A

an alloy of iron and less than 2% carbon

21
Q

What happens if the carbon content of steel is increased beyond 2%?

A
  • brittle
  • unsuitable for cold working
22
Q

In solid state, a variety of strcutures are adopted by steel, depending on what?

A

carbon content and temperature

23
Q

When does steel have an austenite structure?

A

above 723 degrees C

24
Q

What is an austenite structure of steel?

A

an interstitial solid solution of carbon in a FCC iron matrix

25
Q

At what temperature do 2 phases of steel exist?

A

below 723 degrees C

26
Q

What 2 phases of steel exist below 723 degrees C?

A

Ferrite
- dilute solid solution of C (up to 0.02%) in Fe

Cementite
- specific compound Fe3C

27
Q

What is a mixture of ferrite and cementite termed?

A

pearlite

28
Q

What does 0.8% carbon in steel give?

A

eutectoid alloy

29
Q

What is the critical temperature of steel?

A

Tc = 723 degrees C

30
Q

How is the hardness of steel customised?

A

heat treatments

31
Q

In a phase diagram where is the hypo eutectoid alloy?

A

to the left of the eutectic alloy line

32
Q

In a phase diagram where is the hyper eutectoid alloy?

A

to the right of the eutectic alloy line

33
Q

What does being a hypo or hyper eutectoid alloy depend on?

A

percentage of carbon present

34
Q

What is an example of a hypereutectoid alloy?

A

cementite - hard, brittle
- cutting instruments e.g. burs

35
Q

What is an example of a hypoeutectoid alloy?

A

ferrite - softer and more ductile
- non cutting instruments such as forceps

36
Q

What is stainless steel?

A

steel with the addition of chromium

37
Q

In stainless steel, what does chromium improve?

A

improves corrosion resistance by passivating effect

38
Q

What may be added to stainless steel?

A

may also add Ni to increase corrosion resistance and strength

39
Q

What effect does the addition of both chromium and Ni to steel have?

A

reduces the Tc

40
Q

What is 18/8 stainless steel?

A

18% chromium and 8% Ni

41
Q

Is 18/8 stainless steel amenable to heat treatment? Why?

A

no - Tc is below where atomic movements are possible
- therefore rely upon cold working to form wrought structure e.g. non-cutting instruments, wires, denture bases

42
Q

What can 18/8 be soldered and welded?

A

yes

43
Q

What grades is 18/8 stainless steel available in?

A

3 grades: soft, half hard, hard

depends upon carbon content, these grades exist where the carbon content is less than 0.15%

44
Q

How may 18/8 stainless steel be joined?

A
  • solder - with Ag solder
  • welding - pressed together and heated
45
Q

In welding, what is the temperature change proportional to?

A

I^2Rt

where I = current, R= electrical resistance and t= time current passes

46
Q

What is martensitic stainless steel?

A
  • no Ni, 12% chromium
  • heat treatments possible
  • probes and cutting instruments
47
Q

What is springback ability of wire?

A

ability to undergo large deflections without permanent deformation
- springback potential = yield stress/modulus of elasticity

thickness affects stiffness

BDS M5 Dental Materials (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions