Brainscape's Knowledge GenomeTM

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


See full index

Year 3 Operative and endo > Casting Alloys > Flashcards

Casting Alloys Flashcards

1
Q

advantages of alloys 4

A
  • cost
  • biocompatibility (corrosion and tarnish resistance)
  • mechanical properties (stiffness, strength, hardness
  • ease of casting (low melting point, shrinkage, density)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

examples of alloys used in dentistry

A
  • amalgam
  • steel alloys, nickel titanium alloys ( instruments, endo/ortho wires)
  • gold, cobalt-chrome alloys (crowns, inlays, onlays, bases)
  • titanium alloys (implants and fixed or removable partial denture)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define 4 fabrication processes of alloys

A
  1. forming: plastic deformation, hot or cold working eg forging, rolling, extrusion, drawing
  2. amalgamation: blending mercury with other metals
  3. casting: pouring metal in to mould
  4. powder metallurgy: sintering, injection moulding, 3D printing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

typical steps in dental alloy casting

A
  • prepare dentition
  • prepare impression
  • pour model
  • wax desired shape
  • invest wax pattern
  • burn-out and heating the mould
  • melting and casting the alloy
  • finishing and polishing
  • heat treatment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

ideal physical properties of dental alloys 3

A 
low melting point (good flow)
high density (castability)
low coefficient of thermal expansion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is an alloy

A

mixture of metals

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

ideal chemical properties of dental alloys 2

A

chemical corrosion/ tarnish resistance

electrochemical corrosion resistance

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

ideal mechanical properties of dental alloys 3

A 
high modulus (stiffness)
high yield strength (resistance to plastic deformation)
hardenable by heat treatment (retention of polish)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

ideal biological properties of dental alloys 2

A

biocompatible (no toxic soluble phases)

non-reactive in oral environment

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

2 types of casting metal alloys

A
  1. noble alloys (gold, silver-palladium, platinum). resist oxidation, tarnish, corrosion during heating, casting, soldering
  2. base metal casting alloys (cobalt-chrome, nickel-chromium, titanium alloys)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

list the 6 platinum group noble metals PPIORR

A 
platinum
iridium
osmium
palladium
rhodium
ruthenium
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what does precious metal mean

A

how expensive it is. term not used

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

in what noble metal does small amounts of impurities have pronounced and detrimental effect on properties

A

gold

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

what is the best noble alloy and why

A

gold. softest, malleable, ductile.
tarnish resistant in air and water at any temp
insoluble in sulphuric, nitric, hydrochloric acids

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

what is gold soluble in?

A

conc nitric acid and hydrochloric acid (aqua regia)

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

which noble alloy has higher melting point than porcelain?

A

platinum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

when is palladium used and why?

A

dental casting alloys (cheaper than platinum)
helps prevent corrosion of silver in oral environment
absorbs H2 gas when heated properly

18
Q

what is the best known conductor of heat and electricity?

A

silver

19
Q

disadvantage of silver

A

combines with sulphur, chorine and phosphorus when not in clean dry air –> tarnish (eg in mouth)
occludes O2 in molten state

20
Q

2 minor alloying elements

A

iridium (Ir)

ruthenium (Ru)

21
Q

why are minor alloying elements used 4

A 
to increase alloys :
-tensile strength >30%
-tarnish resistance >30%
- yield strength
-elongation. 
50ppm --> x100 increase in number of grains per unit volume
22
Q

types of gold alloy

A 
I: soft (highest % gold, 85%)
II: medium 75%Au
III: hard 70%Au
IV: extra hard 65%Au
each contains Ag, Cu, Pt/Pd, Zn in that order
23
Q

measure of gold in alloy

A

karat/ carat (parts of pure gold per 24)

fineness (parts of pure gold per 1000)

24
Q

why are the following used in gold alloys comp II

  1. copper
  2. silver
  3. platinum and palladium
  4. zinc
A
  1. copper: increase strength, tarnish resistance. dec melting temp
  2. silver: increase strength, better colour than red copper
  3. platinum and palladium: inc strength and melting temp
  4. zinc: prevent oxidation, improve castability
25
Q

how does each of the following properties change with increasing % of gold

a) hardness, modulus elasticity, tensile strength
b) prop limit, elongation, melting temp, corrosion resistance

A

a) decrease

b) increase

26
Q

uses of each type of gold casting alloy

A

I: inlays which are well-supported and no large masticatory forces. high ductility allows burnishing- improves hardness and fit
II: inlays. less ductile but better mechanical properties
III: inlays, onlays, full-coverage crowns, short-span bridges (areas with less support and opposing stress)
IV: extensive use of construction of partial denture components, long span bridges

27
Q

compare properties of low gold content alloys to casting gold alloys

A

similar to type III and IV except ductility which is significantly lower

28
Q

compare uses of low gold content alloys to casting gold alloys

A

same casting technique and usage but lower cost

29
Q

% components of silver palladium alloys

A

mostly silver
25% palladium
small amounts of copper, zinc, indium, gold

30
Q

give 3 examples of base metal casting alloys and their uses

A

(do not contain noble metals)

  • nickel-chromium: crown and bridge casting
  • cobalt-chromium: partial denture framework casting
  • titanium and titanium-aluminium-vanadium alloys: implant
31
Q

why is molybdenum present and where

A

to refine grain size in cobalt (nickel-chromium) alloys

32
Q

cobalt/ nickel-chromium alloys:

  1. % composition
  2. melting point
  3. modulus
  4. Vickers hardness number
A

cobalt/ nickel-chromium alloys:

  1. % composition: 60% cobalt (nickel), 30% chromium
  2. melting point: 1300-1500 C
  3. modulus: 250GPa (gold= 70-100GPa)
  4. Vickers hardness number: 350-400 (type IV gold hardened= 250-300)
33
Q

properties of composition I cobalt/nickel-chromium alloys

A

cobalt/nickel 65-78%

chromium >25%: responsible for corrosion/ tarnish resistance due to passivity

34
Q

what happens if >30% chromium

A

difficult to cast, brittle

35
Q

compare nickel to cobalt alloys

A

nickel decreased strength, hardness, MOE, fusion temp

increased ductility, elongation

36
Q

properties of composition II cobalt/nickel-chromium alloys 2MC

A

minor alloying elements control physical properties:

  • carbon (0.1-0.5%) inc strength, hardness, brittleness. inc by 0.2% –> too hard and brittle for dental use. dec by 0.2% –> dec yield strength to unacceptable levels
  • molybdenum (3-6%) inc strength, hardness, % elongation
37
Q

properties of composition III cobalt/nickel-chromium alloys

3AB

A

-aluminium (4-5%): forms Ni3Al in NiCr alloys –> precipitation, inc tensile and yield strength
-beryllium (0.5-2%): dec fusion temp by 100C
inc fluidity during casting
allows for electrolytic etching (with resin bond proshesis)

38
Q

properties of composition IV cobalt/nickel-chromium alloys

A
  • manganese (5%) and silicon (0.5%): inc fluidity and castability of molten alloy
  • boron –> deoxidizers (in nickel-containing alloys)
  • iron and copper: inc hardness
39
Q

properties of titanium

A
  • light weight (4.5g/cm3)
  • biocompatible
  • corrosion resistant (TiO2 surface from passivation)
  • low cost
40
Q

use of titanium v titanium alloys

A

titanium: implants, crowns, partial and complete dentures

Ti-6Al-4V: stronger, smaller diameter implants

41
Q

problems in casting titanium alloys

A
  • high melting point (1700c)
  • chemical reactions with gaseous elements
  • -> need well-controlled vacuum in processing, technology is expensive

Year 3 Operative and endo (6 decks)

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