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BDS2: DM > Amalgam > Flashcards

Amalgam Flashcards

1
Q

What Amalgam contain?

A
  • Silver
  • Tin
  • Copper
  • Zinc
  • Palladium
  • Indium
  • Mercury
    (STiCZPIM)
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2
Q

Definition of Dental Amalgam

A

When Mercury is mixed with silver tin alloy

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3
Q

Low copper Amalgam composition

A
  • 67 -74% Silver
  • 25 -28% Tin
  • 0 - 6% Copper
  • 0 - 2% Zinc
    + Mercury
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4
Q

High Copper Amalgam composition

A
  • 40 - 70% Silver
  • 21 - 30% Tin
  • 12 - 30% Copper
  • 0 - 1% Zinc
  • 0 - 0.5% Palladium
  • 0 - 4% Indium
    + Mercury
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5
Q

Function of Silver in Amalgam

A

Increases

  • Strength
  • Tarnish and Corrosion Resistance
  • Expansion

Decreases

  • Flow and Creep
  • Setting Time
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6
Q

Definition of Amalgam

A

When mercury is mixed with another metal

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7
Q

Function of Tin in Amalgam

A

Increases

  • setting time
  • flow and creep

Decreases

  • strength
  • expansion
  • corrosion resistance
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8
Q

Function of Copper in Amalgam

A

Increases

  • Strength and hardness
  • Tarnish and corrosion resistance
  • expansion

Decreases

  • Flow and Creep
  • Setting Time
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9
Q

Function of Zinc in Amalgam

A
  • Acts as Scavenger

- Decreases oxidation of other metals

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10
Q

Function of Mercury in Amalgam

A

Activates the reaction

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11
Q

Function of Palladium in Amalgam

A

Increases

  • Tarnish and Corrosion Resistance
  • Strength
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12
Q

Function of Indium in Amalgam

A

Increases

  • Strength
  • Expansion
  • Setting time

Decreases

  • Flow and Creep
  • Surface Tension and thus reduces amount of Hg needed
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13
Q

How do you form Lathe-cut particles?

A
  • Heat ingot to homogenise (400C for 8hrs)
  • Cut particles from ingot
  • Anneal particles at 100C
  • Treat surface with acid to increase reactivity
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14
Q

How do you for Spherical Particles?

A
  • Atomise molten alloy
  • Quench
  • Acid Wash to increase reactivity
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15
Q

Lathe-cut VS Spherical

A

Spherical

  • Less mercury 40-45%
  • Less mixing time
  • Lower condensation pressures
  • Harden quicker
  • Smoother surface
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16
Q

What categories can you classify Dental Amalgams based on? 4

A
  • Cu Content
  • Zn Content
  • Alloy
  • Shape
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17
Q

Conventional Amalgams 2

A
  • Lathe cut Ag3Sn - Spherical Ag3Sn
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18
Q

High Cu Amalgams (Admix) 2

A
  • Lathe cut Ag3Sn + spherical Ag-Cu

- Lathe cut Ag3Sn + spherical Ag-Sn-Cu (or Ag-Cu-Pd)

19
Q

High Cu Amalgams (Single shape) 2

A
  • All spherical Ag-Sn-Cu

- Lathe cut Ag-Sn-Cu

20
Q

Quaternary Alloy Amalgam 1

A

Ag-Sn-Cu-In

21
Q

Setting Reaction Process

A
  • Mercury initially dissolves the surface of the alloy particles
  • New mercury with alloys is formed
  • Need to condense before crystallisation of new alloys
  • Reaction is never complete
  • Set amalgam contains unreacted Ag3Sn in a matrix of the newly formed alloys
  • A ‘cored structure’
22
Q

Conventional Low Cu Alloys Setting

A
  • Hg dissolves Ag and Sn from alloy
  • New inter-metallic compounds formed
  • Ag2Hg3 – γ1
  • Sn7-8Hg – γ2
23
Q

Gamma Phase (γ) Ag3Sn Properties 3

A
  • Unreacted Alloy
  • Strongest phase and corrodes 2nd least
  • Forms roughly 30% of volume of set amalgam
24
Q

Gamma 1 Phase (γ1) Ag2Hg3 Properties 4

A
  • Matrix for unreacted alloy
  • 2nd Strongest phase and corrodes least
  • Forms roughly 60% of volume
  • Fills gaps between Ag3Sn
25
Q

Gamma 2 Phase (γ2) Sn7-8Hg Properties 4

A
  • Weakest and softest phase
  • Corrodes fast, voids form
  • Forms roughly 10% of volume
  • Volume decreases with time due to corrosion
26
Q

Setting reaction for Admixed high copper alloy

A
  • Hg dissolves Ag from Ag-Cu spherical eutectic particles
  • Hg dissolves Ag and Sn from Ag3SN particles

Reaction

  • γ + Hg -> γ + γ1 + γ2
  • AgCu remains unreacted
27
Q

Final Reaction for Admixed High Copper Alloys

A

Sn7-8Hg+ Ag-Cu → Cu6Sn5 + Ag2Hg3

28
Q

Single Phase High Copper Setting Reaction

A

(γ + Cu3Sn) + Hg -> γ + Cu3Sn + γ1 + Cu6Sn5

29
Q

Why does Single phase higher copper alloy corrode the least?

A

No γ2 in final set product

30
Q

Structure of Single Phase High Copper Alloy

A

γ with Cu3Sn coating

31
Q

Modern Amalgam Shrinkage process

A
  • Initial shrinkage for roughly 20mins
  • Expansion from growth of cyrstalline phases
  • More Mercury = More expansion
  • Stable after 6-8 hours

OVERALL NET SHRINKAGE

32
Q

Reasons for higher shrinkage

A
  • Particle Size Smaller
  • Higher Hg/Alloy Ratio
  • Trituration time longer and more rapid
  • Condensation pressure higher
33
Q

Visual properties of Properly triturated Amalgam

A
  • Shiny

- Separates from capsule in a single mass

34
Q

What is condensation?

A

Packing incrementally into the cavity

35
Q

3 types of finishing

A
  • Carving
  • Burnishing
  • Polishing
36
Q

What Element causes Delayed Expansion?

A
  • Zn

Zn + H2O -> ZnO + H2

37
Q

What compound is Tarnish?

A

Black Silver Sulphide

No long term Problems

38
Q

Order of corrosion in pure phases?

A
  • γ1
  • γ
  • Ag3Cu2
  • Cu3Sn
  • Cu6Sn5
  • γ2
39
Q

Types of corrosion in Amalgam 3

A
  • Galvanic Corrosion
  • Crevice Corrosion
  • Stress Corrosion
40
Q

Mechanical Properties of Amalgam

A
  • High Compressive Strength
  • Good Wear Resistance
  • Mercury content must be < 50% for optimum results
41
Q

Disadvantages of Dental Amalgams

A
  • Non Adhesive (relies on mechanical retention)
  • Conducts Heat
  • Corrosion and Tarnish
  • Poor Aesthetics
  • Brittle
  • Viscoelastic (creep)
42
Q

What is marginal breakdown?

A

Thin layers of amalgam fracture easily as it is brittle

Known as ‘Ditching’

43
Q

How does the manufacturer affect the quality of Amalgam?

A
  • Alloy Composition
  • Heat Treatment
  • Size, Shape and production method of particles
  • Particle surface treatment
  • Where it is supplied from
  • Mercury:Alloy Ratio
44
Q

How does the dentist affect the quality of Amalgam?

A
  • Trituration Procedures
  • Cavity Design
  • Condensation Technique
  • Marginal Integrity
  • Anatomy

BDS2: DM (6 decks)

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