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Dental Materials Second Half Sem > Dental Alloys > Flashcards

Dental Alloys Flashcards

1
Q

what are some common metaic dental biomaterials?

A

-amalgam
-casting alloys
-titanium and titanium alloys (implants)
* Stainless steel (Tools)
* Co-Cr (Cobalt-Chromium) alloys
(Implants, lab, restorations)
* Ni-Ti (Nickel-Titanium) alloys
(brackets)

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2
Q

what are casting alloys?

A

used to mold alloys

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3
Q

what are noble metals?

A

Defined by their high resistance to corrosion. In dentistry:
- Gold (Au)
- Palladium (Pd)
- Platinum (Pt)

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4
Q

What are base metals?

A

High tendency to corrode in
oral environment. In dentistry:
- Nickel (Ni)
- Copper (Cu)
- Silver (Ag)
- Cobalt (Co)
- Zinc (Zn)
- Titanium (Ti) - exception no
corrosion

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5
Q

what are some pros of gold alloys?

A
  • Best known of dental metals
  • Excellent resistance to
    corrosion
  • Good malleability
  • Low melting point (1064C)
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6
Q

what are some pros of Palladium alloys?

A
  • Excellent corrosion resistance
  • Medium melting point (1554C)
  • Much harder than gold (not
    practical use in pure form)
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7
Q

When Palladium is mixed with Au what properties change?

A

-Increase hardness
-Increase melting temp
-Whiten the color

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8
Q

what are some pros of Platinum alloys?

A
  • High melting point (1772C)
  • Harder than Pd
  • Low dental use due to mixing
    and price
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9
Q

how are alloys charactarized?

A

Categorized on the basis of noble metal content (NOT BASE)

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10
Q

when is something considered to have a high alloy content?

A

over 60% noble and gold content

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11
Q

when is something considered to be noble alloy?

A

over 25% noble composition
(any less than not considered noble)

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12
Q

what are some properties of high noble alloys?

A
  • Expensive
  • High densities (> 13 g/cm3) —> easy to cast
  • Copper and Silver often added to increase hardness or strength
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13
Q

noble alloys have _____ resistance

A

excellent corrosion

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14
Q

high noble generally to not have ____ moduli

A

high

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15
Q

why cant Au-Ag-Cu alloys cannot be use in ceramic-alloy?

A

due to low melting point

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16
Q

what are some properties of noble alloys?

A

-compositionally diverse
-moderate density
-higher or equal strength to high noble due to Pd
low cost

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17
Q

Predominantly Base-Metal Alloys properties are:

A

-most complex (contain 6-8 elements)
-high yield strength and hardness (makes difficult to polish)
-low density making it hard to cast

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18
Q

what are some examples of mechanical and physical alloys properties?

A
  • Melting range
  • Young’s Modulus and Strength
  • Hardness
  • Casting Shrinkage
  • Density
  • Color
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19
Q

why do alloys have a melting range?

A

because they are a composition of different medals

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20
Q

what is the difference between the liquidus and solidus temperature?

A
  • Liquidus: temperature at which all alloy melts (upper range)
  • Solidus: temperature at which all alloy “freezes” (lower range)
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21
Q

what is alloy modulus and strength relevant for?

A

clinical success and prevention of restoration failure (bear occlusal forces)

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22
Q

high modulus is required for what?

A

resist occlusal forces

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23
Q

should have enough strength to resist:

A

permanent deformation

24
Q

what is hardness?

A

Indication of how easy the alloy is to indent or to polish

25
Q

high yield strength and high hardness is related to:

A

increased difficulty to polish

26
Q

for a resteration would you select an alloy harder than enamel?

A

no because it dan deform the enamel of the opposing tooth

27
Q

When do all metals expand/shrink??

A

Expand on heating (increase interatomic distances)
* Shrink on cooling (decrease interatomic distance)

28
Q

Alloys with little _____ and ____ _____ are able to produce more accurate casting

A

solidification and cooling shrinkage

29
Q

metals are:

A

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

30
Q

alloys are:

A
  • the mix of two or more substances where at
    least one of them is a metal.
  • For example: steels, cast iron, amalgam, Co-Cr
    alloys
31
Q

what is the composition of Amalgam?

A

Silver Alloy + Mercury + Small quantity of zinc and palladium

32
Q

what is the composition of the high copper alloy?

A

13-30% Cu
* Higher strength
* Less corrosion
* Less creep
* Better longevity at the margins
* Reduced corrosion (In and Pd

33
Q

what is the composition of the low copper alloy?

A

2-4% Cu (more tin)
* Zn causes long-term expansion due
to moisture
* ADA Standard <0.01% wt
* Replaced by High-Copper

34
Q

what is the significance of the shape of silver alloy powder?

A

-influence the properties of amalgam
-irregular, spherical and combination shapes

35
Q

What is amalgamation and what does it form?

A

-Copper, silver, and tin dissolve into the mercury
-forms amalgam matrix

36
Q

Dissolved elements form new ___ ____ and the crystalliation of them will continue till?

A

solid products, liquid mercury is consumed

37
Q

what are clinical properties of amalgam?

A
  • Mechanical Strength
    –Compression
    –Tension
  • Dimensional Change
  • Creep
  • Tarnish and Corrosion
38
Q

amalgam is a classic ____ material

A

brittle (only elastic, no plasticity)

39
Q

what composition in amalgam controls the strength?

A

mercury content

40
Q

how does amalgam strength change over time?

A

Strength changes with time after restoration placement (causes risk for fracture and failure)

41
Q

when does amalgam reach its max strength?

A

7 days

42
Q

what dimensional changes occur during setting?

A
  • CONTRACTION during alloy dissolution
  • EXPANSION during impingement of reaction product crystals
43
Q

The ___ ____ during the setting of amalgam is one of its most significant properties

A

dimensional change

44
Q

creep is associated with :

A

breakdown at the margins of restoration (loss of marginal integrity)

45
Q

what is corrosion?

A

Corrosion is the progressive destruction of a metal by
chemical or electrochemical reaction with its environment

46
Q

what can occur with corrosion of amalgam?

A
  • increased porosity
  • Reduced marginal integrity
  • Loss of strength
  • Release of metallic ions to oral environment
47
Q

what are corrosion products of amalgam?

A
  • Tin oxides, tin hydroxychlorides, copper oxides
  • Due to environment with salty solutions
  • Saliva may provide corrosion protection (protein pellicle)
48
Q

how long does mercury take to leave the body?

A

up to 300 days
(in service, amalgam generates minimal amount of mercury vapor)

49
Q

who should not get mercury fillings?

A

-pregnant or soon to be pregnant
-nursing women
-children (esp under 6)
-neuro issues
-impared kidney function

50
Q

what are some properties of titanium alloys?

A
  • Excellent corrosion resistance (almost equivalent to
    platinum)
  • Low toxicity
  • Very low allergenic potential and high
    biocompatibility
  • Chemically inert (no release of ions)
  • Excellent mechanical properties
  • Light/strong metal, easy to manufacture
  • Low thermal conductivity
51
Q

what is the most common titanium formation?

A
  • Commercially Pure titanium (cp-Ti)
    -Grades 1-4
  • Titanium–aluminum–vanadium (Ti–6Al–4V)
52
Q

what is Cp-Ticomposituon

A

Titanium: 99%, Oxygen: 0.2-0.4%, Traces Fe, H and Ni:
0.25%

53
Q

the amount of _____ determines the grade of the titanium alloy

A

oxygen

54
Q

what is the composition of ti alloys?

A

90% Titanium, 6% Aluminum, 4% Vanadium

55
Q

Ti Alloys (Ti6Al4V) have what compated to cp-ti?

A

improved strength

56
Q

what is an oxide layer?

A

–Titanium spontaneously forms a oxide surface on exposure to
air or physiologic saline environment
* Self-healing layer
* Inhibits low-charge transfer (biocompatibility)
* Prevents corrosion (good osseointegration)

57
Q

coating on dental implants have what benefit?

A

-antibacterial
-improve osseointegration
-antibiotics

Dental Materials Second Half Sem (6 decks)

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