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Dental Materials Y2 > Dental Amalgams > Flashcards

Dental Amalgams Flashcards

1
Q

What is an amalgam made out of

A

When mercury is mixed with another metal like gold, tin or silver

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2
Q

What is considered the best and most cost effective amalgam option for restorations

A

Mercury + silver tin alloy

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3
Q

What metals are found in the conventional (low copper) alloy of amalgam

A

67%-74% Silver (gamma phase Ag3Sn)
25-28% - Tin
0-6% copper
0-2% zinc

this alloy is added to mercury

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4
Q

Describe the modern high copper amalgams alloy composition

A 
40-70% silver
21-30% tin
12-30% copper
0-1% zinc
0-0.5% palladaium
0-4% indium

alloy is added to mercury

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5
Q

What does adding silver in an amalgam alloy increase

A
  • Strength
  • Tarnish and corrosion resistance
  • Expansion
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6
Q

What does adding silver in an amalgam alloy decrease

A
  • Flow and creep

- Setting time

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7
Q

What does adding tin to an amalgam alloy increase

A
  • Setting time

- Flow and creep

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8
Q

What does adding tin to an amalgam alloy decrease

A
  • Strength
  • Expansion
  • Corrosion resistance
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9
Q

What does adding copper to an amalgam alloy increase

A
  • Strength and hardness
  • Tarnish and corrosion resistance
  • Expansion
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10
Q

What does adding copper to an amalgam alloy decrease

A
  • Flow and creep

- Setting time

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11
Q

What does adding zinc to an amalgam alloy do

A

Acts as a scavenger and decreases the oxidation of other metals

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12
Q

What is the role of mercury in an amalgam alloy

A

Activates the reaction

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13
Q

What does adding palladium to an amalgam alloy increase

A
  • Tarnish and corrosion resistance

- Strength

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14
Q

What does adding Indium to an amalgam alloy increase

A
  • Strength
  • Expansion
  • Setting time
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15
Q

What does adding Indium to an amalgam alloy decrease

A
  • flow and creep

- surface tension and so the amount of mercury required it less

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16
Q

What shapes of particles does the dental amalgam alloy powder come in

A

Lathe-cut

Spherical

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17
Q

How are lathe cut amalgam alloys formed

A

Block of alloy with gamma and beta phases is homogenised at 400C for up to 8 hours to form gamma phase.
Particles of this block are annealed at 100C to relieve internal strains.
This is then surface treated with acid to increase reactivity and remove oxides from surface

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18
Q

What size of particle can lathe cut amalgam alloys be

A

Micro cut
Fine cut
Coarse cut

Between 60-100um long
10-70um wide and 10-35 thick

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19
Q

How are spherical amalgam alloys created

A

Spherical particles are produced by atomising molten alloy in an inert atmosphere.

Acid washed to increase reactivity

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20
Q

What is the typical particle size of spherical amalgam alloy particles

A

5-50um

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21
Q

How do spherical particles compare to lathe cut particles in amalgam alloys

A
  • Requires less mercury - 40-45%
  • Require less mixing time
  • Require lower condensation pressures
  • Harden more rapidly
  • Smoother surface
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22
Q

What are the different ways that you can classify dental amalgams

A
  • Based on Cu content
  • Based on Zn content
  • Based on alloy
  • Based on shape
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23
Q

How can you classify dental amalgams based on Cu content

A

Low Cu alloys

High Cu alloys

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24
Q

How can you classify dental amalgams based on Zn content

A

Zn containing

Zn free

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25
Q

How can you classify dental amalgams based on the alloys

A

Binary
Ternary
Quaternary

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26
Q

How can you classify dental amalgams based on their shaped

A
  • Lathe cut
  • Spherical allots
  • Admix (dispersed phase)
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27
Q

Describe the setting reaction of dental amalgams

A
  • Mercury initially dissolves the surface of the alloy particles
  • New mercury containing alloys formed
  • Reaction is never complete
  • Set amalgam contains unreacted Ag3Sn in a matrix of the newly formed alloys.
  • A “cored structure”
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28
Q

What are the gamma 1 and gamma 2 compounds found in between Ag-Sn alloys (i think)

A 
Ag2Hg3 = gamma 1
Sn7-8Hg = gamma 2
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29
Q

What phases are found in the low copper, conventional, set amalgam structure

A

Gamma phase
Gamma 1 phase
Gamma 2 phase

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30
Q

Describe the gamma phase of conventional low copper dental amalgams

A

Ag3Sn

  • Unreacted alloy
  • Strongest phase and corrodes the 2nd least
  • Forms ~30% of volume of set amalgam
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31
Q

Describe the gamma 1 phase of conventional low copper dental amalgams

A

Ag2Hg3

  • Matrix for unreacted alloy found around and in-between AgSn alloy
  • 2nd strongest and corrodes the least
  • Forms ~60% of volume
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32
Q

Describe the gamma 2 phase of conventional low copper dental amalgams

A

Sn7-8Hg

  • Weakest and softest phase
  • Corrodes fast, voids form
  • ~10% of volume
  • Volume decreases with time due to corrosion
  • Found in between the gamma 1 phases and AgSN alloys
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33
Q

Describe the first setting reaction of Admixed high copper alloys

A
  • Hg dissolves Ag and Sn from Ag3Sn particles
  • In the first reaction AgCu remains unreacted
  • Gamma + Hg = Gamma + Gamma 1 + Gamma 2
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34
Q

Describe the second setting reaction of admixed high copper alloys

A
  • Gamma 2 (Sn7-8Hg) reacts with AgCu to form Cu6Sn5

- This forms the eta phase that surrounds the unconsumed AgCu particles as well as gamma 1 phase

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35
Q

Describe the structure of single phase high copper dental amalgams

A

Gamma (AgSn) phase coated in epsilon (Cu3Sn) coating

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36
Q

What happens in the first setting reaction of single phase high copper dental amalgam

A

Ag and Sn dissolve in Hg

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37
Q

What happens in the second setting reaction of dental amalgams

A

Gamma 1 (Ag2Hg3) crystals grow binding gamma (Ag3Sn) particles together

Eta crystals (Cu3Sn) form within gamma 1

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38
Q

Write down the setting reaction of single phase high copper dental amalgam

A

(Gamma + Eta) + Hg = Gamma + Eta + Gamma 1 + eta

39
Q

What contributes to the net shrinkage of all modern amalgams

A
  • Initial shrinkage from dissolution of the alloy
  • Expansion from growth of crystalline phases
  • The higher the mercury content the higher the expansion
  • Final bit of shrinkage due to final contraction caused by solid state reactions
  • Stable after 6-8 hours
40
Q

What contributes to higher shrinkage

A
  • Smaller particle size, more dissolution
  • Higher Hg/Alloy ratio, more dissolution
  • Trituration time longer and more rapid, more dissolution
  • Condensation pressure higher, lower mercury and less new alloy formed
41
Q

What is trituration

A

Mixing of dental amalgams

42
Q

What is speed and time is usually used in trituration

A

Around 3000 rpm

For about 5-20 seconds

43
Q

What is the dental amalgam powder mixed with

A

Powder is mixed with 40-50% mercury, higher amount for low copper

44
Q

What does under triturated alloy powder look like

A

Dull, dry, crumbly mix

45
Q

What does properly triturated alloy powder look like

A

Shiny mix, separates from capsule in single mass

46
Q

What does over triturated alloy powder look like

A

Shiny, hot, wet mix, sticks to capsule

47
Q

What is condensation in dental amalgams

A

This is when you pack the amalgam into the tooth cavity incrementally

48
Q

Why is condensation used for dental amalgams

A
  • removes excess mercury by bringing mercury to the top of the surface
  • Prevents voids
  • Gives optimum marginal adaptation
49
Q

What is roughly the final mercury content of lathe cut and spherical dental amalgams

A

Lathe Cut = 45%

Spherical = 40%

50
Q

Describe the relationship between condensation pressure and strength for lathe cut and spherical dental amalgams

A

Lathe cut - high strength under lower condensation pressures, doesn’t increase much with condensation pressure

Spherical - Needs higher condensation pressures to reach the levels of strength of lathe cut amalgams

51
Q

What 3 processes of finishing can be done for amalgams

A

Carving
Burnishing
Polishing

52
Q

What gives the better surfacee finish, spherical or lathe cut amalgams

A

Spherical

53
Q

What is burnishing

A

This is the process of smoothing out surfaces with pressure, helps to remove residual mercury from the surface and improves margins

54
Q

Why might a patient complain about pressure after having a zinc containing amalgams

A

Zinc containing amalgams undergo delayed expansion when they are contaminated with water, the zinc will react with the water and produce hydrogen

55
Q

What is tarnishing

A

The formation of black silver sulphide that can be polished off and does not cause long term problems, has no effect on clinical lifetime

56
Q

List the order of corrosion resistance by the phases found in dental amalgams

A

Gamma 1 > Gamma > Ag3Cu2 > epsilon > eta> gamma 2

57
Q

What is the most prone phase in low copper amalgams and what are the corrosion products

A

Low copper gamma 2 phase is the most prone and the corrosion products are tin oxides and chlorides

58
Q

What is the most prone phase in high copper amalgams and what are the corrosion products

A

High copper Eta phase is the most prone to corrosion, the products of corrosion = tin oxides, chlorides and copper chlorides.

High copper amalgams corrode more slowly than low copper amalgams

59
Q

What is galvanic corrosion and give an example

A

When you have opposing dissimilar metals, where one is more electronegative than the other so one will corrode and the other won’t

e.g. amalgam with gold casting alloy - amalgam will corrode here

60
Q

What is localised galvanic corrosion

A

Occurs between different phases as there is a difference between the electropnegativites of each phase

61
Q

What is Crevice corrosion

A

Plaque build up increases electronegativity with respect to the clean surface

Clean surface is cathode and plaque surface is anode and the plaque surface corrodes

62
Q

What is stress corrosion

A

Occurs under sustained tensile force in a corrosive environment

63
Q

What are the mechanical properties of amalgam

A
  • High compressive strength
  • Good wear resistance
  • Mercury content is critical to strength
  • Must be less than 50%
64
Q

How long do dental amalgams last

A

can last around 12 years, longer than composites

65
Q

What are the disadvantages of amalgam

A
  • Non adhesive - mechanical retention
  • Conducts heat and electricity
  • Corrosion and tarnish
  • Poor aesthetics
  • Amalgam is brittle, weak in thin section
  • Amalgam is visco-elastic - creep
66
Q

Describe the coefficient of thermal expansion of amalgam compared to dentin and what affect this can have

A

Coefficient is much higher than dentin so can result in marginal leakage

67
Q

What properties of amalgams affect the marginal seal

A
  • Coefficient of thermal expansion is much higher than dentin = marginal leakage
  • Low copper amalgams corrode and result in sealing of margins, this process is slower for high copper
  • For all amalgams, metal sulfides will form in tarnish and this will help marginal seal
68
Q

What products are there that can contribute to the marginal seal of dental amalgam restorations

A

Cavity varnishes - resins in a volatile solvent, seals dentin surface and reduce bacterial inflammation

Coat surface and margins with unfilled resin, will delay microleakage until corrosion products seals

69
Q

What do amalgam bonding agents do

A

Contain phosphonate esters or 4-META that supposed to reduce marginal leakage and postoperative sensitivity

70
Q

What is a disadvantage of amalgam bonding agents

A

Need to condense amalgam before polymerisation of bonding agent is complete = technically challenging

71
Q

How can the viscoelasticity of amalgams lead to marginal breakdown

A
  • Creep can lead to flow over the margins and this can create a thin layer of amalgam over the margins
  • These thin layers will fracture and result in marginal breakdown, “ditching”
  • Over filling has a similar effect
72
Q

What ways does the manufacturer control the quality of the amalgam

A
  • Alloy composition
  • Heat treatment of the alloy
  • Size, shape and method of production of the alloy particles
  • Surface treatment of the particles
  • Supplied form (encapsulated)
  • Mercury:alloy ratio
73
Q

What ways does the dentist control the quality of the amalgam

A
  • Trituration procedures
  • Cavity design
  • Condensation technique
  • Marginal integrity
  • Anatomy
74
Q

What 3 forms does mercury exist in and how can each enter the body

A

Elemental Hg - mainly absorbed through the lungs
Inorganic Hg-S - in some industrial processes, mainly through skin and mouth
Organic Hg-(CH3)2 - Fish contaminated with methyl mercury

75
Q

What are the main problems with using mercury amalgams

A

Toxic to patient and also very and for the environment

76
Q

What is the most dangerous way to absorb mercury

A

mercury vapour as Hg has high vapour pressure

77
Q

What is the half life of mercury

A

about 55 days

78
Q

What levels of mercury are considered subtle and dangerous

A

Subtle effects = 30 ug per day

Dangerous = 82 ug per day

79
Q

AY BAWS CAN I HABE DE NOTE PLZ

A

The dose of mercury that a patient will receive from amalgam fillings will be negligible but still needs to be noted

80
Q

What can released mercury in the oral cavity do other than enter the blood

A

React with unreacted gamma phase and leads to expansion

81
Q

Who is most at risk of dental amalgams

A

The dental team

82
Q

What complications in the oral cavity can arise as a result of amalgams

A

Lichenoid lesions - usually associated with old and corroded amalgams
Amalgam tattoo - accidental implantation of silver containing compounds into oral mucosa

83
Q

When might amalgam tattoo occur

A
  • During the removal of an old amalgam
  • Broken pieces-socket-tooth extraction
  • Particles entering surgical would
  • Amalgam dust in oral fluids
84
Q

Where might you see amalgam tattoo in the oral cavity

A

Gingiva
Buccal Mucosa
Alveolar Mucosa

85
Q

What element tried to replace mercury in amalgams

A

Gallium alloys, not that good tho

86
Q

What were the benefits of gallium alloys

A
  • Setting expansion - 1.6%
  • Good compressive strength
  • Low creep
  • Rapid solidification (early polish)
  • Biocompatibility and cytotoxicity similar to conventional amalgam and composites
87
Q

What were the disadvantages of using gallium alloys

A
  • Poor corrosion resistance
  • Prone to delayed expansion, moisture contamination
  • Expensive
  • Very wet mix and difficult to handle
  • Not used much but still available
88
Q

What is consolidated silver made of

A

Spherical alloy particles

89
Q

What is consolidated silver acid treated with

A

Fluoroboric acid

90
Q

What is a problem with consolidated silver as an alternative to amalgams

A

Needs high pressures required to remove voids

As you condense it the particles will strain harden and made condensation difficult

91
Q

What are the benefits and disadvantages of fluoridated amalgams

A

Released fluoride for several weeks but final product was more susceptible to corrosion

92
Q

How much copper can you find in low copper amalgams

A

0-6%

93
Q

How much copper can you find in high copper amalgams

A

12-30%

Dental Materials Y2 (13 decks)

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