Brainscape's Knowledge GenomeTM

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


See full index

Dental Materials YR3 BDS > Metals, alloys and casting > Flashcards

Metals, alloys and casting Flashcards

1
Q

All metals are crystalline. What does crystallinity mean?

A

Metals have regularity, a repeating pattern

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

How many different space lattices can a metal form and which is the most common?

A

14 space lattices

Simple cubic is most common

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

Properties of metals

A
  • Strong bonds (high MP +BP)
  • Good stiffness (modulus of elasticity)
  • Ductile (Can be pulled into wires)
  • Malleable (can be beaten into sheets)
  • Conduct heat and electricity
  • Opaque (non-aesthetic)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is an alloy?

A

An alloy is two or more metals that are mutually soluble in each other in a molten state. Formation of alloys results in enhanced properties.

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

What do alloys of a fine grain structure have?

A

The least permanent deformation during service e.g. higher yield stress values

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Properties of alloys that are important

A
  • Colour: aesthetics
  • Grain size: size of crystals of alloy influenced by cooling rate heat and determines properties like tensile strength
  • Phase structure: level of mixing
  • Corrosion
  • Biocompatibility
  • Thermal properties: melting range, thermal expansion
  • Strength
  • Economic - cost
  • Porcelain bonding
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Precious metal

A

Containing metals of high economic value such as gold, platinum, palladium, silver
How expensive they are

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

Noble metal

A

A precious metal that is resistant to tarnish. This excludes “silver” by definition
Chemical property

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

Low gold alloys

A

Alloys containing <75% gold (less than 50 a/o gold) which means that gold atoms represent less than every other atom

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

Gold-substitute alloys

A

Precious alloys that do not contain gold

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Base-metal alloys

A

Alloys not containing precious metals to impart their corrosion

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

How are classes of alloys classified according to ADA 2003?

A
  • High noble alloys (40% wt Gold, 60% wt noble)
  • Titanium and titanium alloys (85% wt Ti) for implants
  • Noble alloys (25% wt e.g. pallidium)
  • Base metal alloys (<25% wt noble e.g. nickel, chromium)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How are high noble alloys (Gold-Au) classified?

A

Types 1-4 from soft to extra hard. The less gold, the stronger the alloy will be. From type 1-4 the ductility, elongation at break and corrosion will decrease whilst hardness, tensile strength, proportional limit and modulus of elasticity will increase.

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

How can gold be measured?

A 
Carat value (24 is maximum carat gold)
Fineness value (value goes up to 1000 and is more valuable than carat to work out % of gold)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Uses of type 1-4 of high noble alloys

A 
Type 1 (non-heat hardenable): inlay, single surface
Type 2 (non-heat hardenable): inlay, onlay (no thin sections)
Type 3 (heat hardenable): onlay, crown (potential for fracture)
Type 4 (heat hardenable): crown, bridge
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Use of gold in alloy

A

Corrosion resistance

17
Q

Use of copper in alloy

A

Hardness

18
Q

Use of silver in alloy

A

Counteract reddish colour of copper

19
Q

Use of pallidium in alloy

A

Increase MP and hardness

20
Q

Use of platinum in alloy

A

Increase MP (harder than Pd)

21
Q

Use of zinc in alloy

A

Prevents oxidation during melting (O2 getter)

22
Q

What are the 2 types o f corrosion?

A

Chemical corrosion = reaction of metal with oxygen
Electrochemical corrosion: need anode, cathode, circuit and electrolyte. Different electrochemical corrosion categories: galvanic corrosion, local galvanic corrosion, concentration cell corrosion and stress concentration

23
Q

How are noble alloys different from high noble alloys?

A

Noble alloys have higher hardness and yield strength compared to high noble but lower melting range.
Pd-Cu-Ag very strong - used for cast and are 25% stiffer than any high noble alloy.

24
Q

Base metal alloys

A

Consist of Ni-Cr and Co-Cr alloys

80% of RPD are from Co-Cr alloys

25
Q

Composition of base metal alloys

A

Cobalt 35-65%,
Chromium 11-26%
Nickel 0-30%
Molybdenum little amount

26
Q

What are the properties of each components of base metal alloys?

A

Co and Ni are simialr and result in hard alloys.
Ni slightly enhances ductility [percent elongation]
Mo provides strength and hardness to Co-Cr alloys
Cr gives corrosion resistance but it fails in high concentration of Cl-

27
Q

Advantages of base metal alloys

A

+ High modulus of elasticity (they can be used in thin section)
+ Hardness
+ strength
+ low density

28
Q

How are base metal alloys classified for fixed restorations?

A

Type 1: low strength applications e.g. inlays
Type 2: medium strength e.g. large inlays, onlays, crowns
Type 3: high strength e.g bridge pontics
Type 4: extra high strength for very high stress applications e.g. long span bridges and implant superstructures

29
Q

What is biocompatibility?

A

Ability of a material to perform with an appropriate host response in a specific situation

30
Q

Titanium alloy composition

A

Ti6Al4V
Ti 6%
Aluminium and 4% vanadium with coating hydroxyapatite
Al is a stabiliser and V is B stabiliser

31
Q

Why titanium?

A

Lightweight, biocompatible, corrosion resistant (dynamic inert oxide layer), strong and low priced

32
Q

Titanium grades

A

Grades 1-4 from yeild strength 25,000 –> 70,000

33
Q

Why is implant dentistry becoming more common?

A
  • Demographics and increasing wealth: ageing population with increasing wealth
  • Growing pt awareness of benefits of implants over conventional solutions, increasing importance of estehtics
  • Increasing acceptance of implants: long term clinical success of implant treatment
  • Rising number of trained dentists
34
Q

Different types of implant materials

A

Titanium
Zirconia (aesthetics, no allergies, more holistic, biofilm no plaque accumulation, periimplantitis, chipping of crown)
TiZr (stronger than pure titanium and has excellent osteointegration properties)

35
Q

Lost wax casting technique

A

A wax pattern is heated, vaporised and subsequently replaced by a metal.

  1. impression
  2. Die production (positive replica)
  3. Waxing on die (Wax restoration)
  4. Wax investment (sprue)
  5. Investing
  6. Wax burnout
  7. casting
36
Q

Porcelain-Fused to metal: metal important requirements

A

Metal must have the potential to bond to the dental porcelain, need oxide forming elements; possess coefficient thermal contraction compatible with dental porcelains; sufficiently high solidus temp to permit application of low-fusing porcelains

37
Q

How does porcelain bond to metal?

A
  • Physical bonding nil
  • Mechanical bonding: extensive - surface roughness from sandblasting determines degree of mechanical inter-digitation
  • Chemical bonding: occurs by oxide mixing
38
Q

What are the mechanical failures for porcelain-to-metal fracture and porcelain fractures?

A

Porcelain-to-metal fracture

  1. Fractures originating at the metal surface: surface metal contamination, incomplete degassing, under fired opaque porcelain, improper metal thickness, incorrect metal conditioner, reused metal alloy.
  2. Fracture at the opaque and entering the bulk porcelain: porosity at the opaque layer, cracks at the opaque layer, incomplete opaque bonding from firing at too low temp.

Porcelain fractures

  1. Design or procedural errors: too little bulk of metal, sharp edges of porcelain, improper margin design
  2. Malocclusion or impact stresses
  3. Thermal contraction incompatibility: built in stresses generate cracks at pores, thermal fatigue propagates cracks
39
Q

Repair systems for porcelain to metal fractures

A
  1. Silane and acrylic e.g. fusion, George Taub products
  2. silane + composite e.g. PULPDENT porcelain repair kit
  3. Silane and composite e.g. MIRAGE PFM Repair

Dental Materials YR3 BDS (4 decks)

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