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Dental Materials > Lecture 9: Metallic Materials > Flashcards

Lecture 9: Metallic Materials Flashcards

1
Q

what are the common metallic dental biomaterials?

A
  • amalgam
  • casting alloys
  • titanium and titanium alloys
  • stainless steel
  • co-cr alloys (cobalt chromium)
  • ni-ti alloys (nickel-titanium)
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2
Q

what is a casting alloy?

A

high noble, noble and base metals used in labratory and restorations

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3
Q

what are the noble metals and what do they do?

A
  • gold, palladium and platinum
  • high resistance for corrosion
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4
Q

what are the base metals and what do they do?

A
  • nickel, copper, silver, cobalt, zinc and titanium
  • high tendancy to corrode
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5
Q

what are some characteristics of gold?

A
  • best known
  • excellent corrosive resistance
  • good malleability
  • low melting point
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6
Q

what are some characteristics of palladium?

A
  • excellent corrosive resistance
  • medium melting point
  • much harder than gold (not practical by itself)
  • when mixed with gold: increased hardness, melting temp and whitens the color
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7
Q

what are some characteristics of platinum?

A
  • high melting point
  • harder than Pd
  • low dental use due to price and mixing
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8
Q

what is nobility of alloys?

A

sum of weight percentages of the noble metals in the alloy

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9
Q

what are characteristics of high noble alloys?

A
  • expensive
  • high density (easy to cast)
  • copper and silver added to increase hardness and strength
  • addition of Pt or Pd
  • excellent corrosion resistance
  • ## not high moduli
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10
Q

what are characteristics of noble alloys?

A
  • most compositionally diverse
  • moderate densities
  • strength is greater or equal to high noble alloys due to Pd content
  • lower cost than high noble alloys
  • gold based contain about 40% gold
  • higher amounts of silver and copper than high noble
  • au based contain low metlting so cannot be used for ceramic alloy restorations
  • Pd based contains 70% pd and almost no gold
  • Pd-Cu or Ag-Pd used for crowns or fixed partial dentures with or without ceramic dentures
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11
Q

what are characteristics of base-metal alloys?

A
  • minor amounts of noble elements
  • most complex and contains 6-8 elements
  • extremely high yield strength and hardness (difficult to polish)
  • low densities (difficult to cast)
  • least expensive
  • Nickel-cobalt base have high corrosion and questionable bio-compatibility
  • crowns, fixed partial dentures, impalnts
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12
Q

what are the mechanical and physical alloy properties?

A
  • melting range
  • young’s module and strength
  • hardness
  • casting shrinkage
  • density
  • color
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13
Q

explain melting range

A

alloys don’t melt at a single temperature but have a melting range

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14
Q

what is liquidus?

A

temp a which all alloy melts

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15
Q

what is solidus?

A

temp at which all alloy freezes

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16
Q

why is modulus and strength relevant?

A

for clinical success and prevention of restoration failure

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17
Q

why is high modulus required?

A

resist occlusal forces

18
Q

why is high strength needed?

A

to prevent permanent deformation
* can be increased for some alloys by heat treatment

19
Q

explain alloy hardness

A

-indication of how easy it is to indent or to polish
- related and proportional to yield strength

20
Q

all metals do what?

A

expand when heated
shrink when cooled

21
Q

alloys with what two properties are able to produce more accurate casting?

A

little solidification and cooling shrinkage

22
Q

definition of metals

A

any of the several solid material elements that are malleable under heat or pressure and can conduct heat/electricity

23
Q

definition of alloys

A

the mix of two or more substances where at least one is a metal

24
Q

amalgam is an alloy made of?

A
  • silver alloy powder: silver + tin + copper
  • liquid mercury
  • small contents of zinc and palladium
25
Q

what are the two types of silver alloy powder?

A

high copper alloy (13-30%) and low copper alloy (2-4%)

26
Q

what are the differences between low and high copper alloy?

A

high copper alloy has
- higher strength, less corrosion, less creep, better longevity,

low copper alloy has
- zn causing long term expansion

27
Q

what are the three silver alloy powder shapes?

A

irregular, spherical and combination

28
Q

what is amalgamation?

A
  • reaction that forms amalgam matrix where copper, silver and tin are dissolved into the mercury
  • once reaction is complete little to no mercury remains
29
Q

the crystallization of new products during amalgamation continues until???

A

all the liquid mercury is consumed

30
Q

what are the clinical properties of amalgam?

A
  • mechanical strength
  • dimensional change
  • creep
  • tarnish and corrosion
31
Q

what are the mechanical properties of amalgam?

A

brittle material where the Hg concentration controls the strength (maximum after 7 days)
** strength changes with time after restoration placement

32
Q

what are the two types of dimensional changes that can occur during setting?

A
  • contraction (negative) during alloy dissolution
  • expansion (positive) during impingement of reaction product crystals

** most significant property

33
Q

explain creep % of amalgam?

A

associated with breakdown at the margins of the restoration (loss of marginal integrity) where thin margins stretch beyond their limit

34
Q

what is corrosion and what does it lead to?

A
  • progressive destruction of a metal by chemical or electrochemical reaction
  • increased porosity, reduced marginal integrity, loss of strength and release of metallic ions
35
Q

list some of the corrosion products

A
  • tin oxides, tin hydrochlorides, copper oxides

**due to salty environment
** saliva can provide protection

36
Q

why do you want to limit exposure to mercury?

A
  • its toxic
  • slow elimination from the body
37
Q

what is minamata convention?

A

reducing the use of amalgam

38
Q

what are some characteristics of titanium alloy?

A
  • corrosion resistance
  • low toxicity (no release of ions)
  • excellent mechanical properties
  • low thermal conductivity
38
Q

what are the two most common titanium formulations?

A
  • commercially pure titanium
  • titanium-aluminum-vanadium
39
Q

in CP-ti alloy what determines the grade?

A

the amount of oxygen

40
Q

explain the ti-biocompatibility/corrosion protection properties

A
  • oxide layer: titanium spontaneously forms an oxide surface on exposure to air or saline environment
    ** self healing layer, inhibits low charge transfer, prevents corrosion
41
Q

explain dental titanium implants

A
  • implant surfaces are coated for bioactivity
  • silver copper fluoride (antibacterial)
  • improves osseointegration due to porosity

Dental Materials (8 decks)

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