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Sympsoiums yr2 > 5- Dental Amalgam > Flashcards

5- Dental Amalgam Flashcards

1
Q

What is amalgam?

A

An alloy of mercury with another metal

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2
Q

Why do we use amalgam?

A
  • inexpensive material
  • easy to use
  • been used for over 100 years
  • resin-free [so less allergies than composite]
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3
Q

What are the advantages of using amalgam?

A
  • inexpensive
  • rigid
  • strong
  • wear resistance
  • durable
  • easy to manipulate
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4
Q

What are the disadvantages of using amalgam?

A
  • bad aesthetics
  • mercury hazard
  • MARGINAL DITCHING : [CREEP AND CORROSION RISK]
  • non-bonding (doesn’t rely on adhesive so more tooth tissue is removed)
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5
Q

What are 2 different types of amalgam cut you can have?

A
  1. Irregular (lathe-cut)

2. Spherical (atomised)

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6
Q

What are the 2 different sizes of amalgam cuts?

A
  1. Fine cut [35 nanometers]

2. Micro cut [25 nanometers]

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7
Q

What do the properties of amalgam depend on?

A

Alloy composition i.e material

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8
Q

What do the handling characteristics of amalgam depend on?

A

Shape and size of the alloy particle

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9
Q

Narrow head condenser?

A

Irregular alloy particle

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10
Q

Wide head condenser?

A

Spherical alloy particle

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11
Q

On average how much silver is in amalgam?

A

70

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12
Q

Difference between conventional and blended amalgam?

A

Blended contains much higher copper count (13)

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13
Q

What is the primary reaction of amalgam?

A

Reaction of alloy with mercury

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14
Q

State primary reaction equation?

A

Ag3Sn + Hg –> Ag2Hg3 + Sn7Hg + Ag3Sn

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15
Q

What is gamma 1 phase?

A

Silver mercury [Ag2Hg3]

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16
Q

What is gamma 2 phase?

A

Tin mercury [Sn7Hg]

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17
Q

What is the unreacted core i.e gamma phase?

A

Ag3Sn

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18
Q

Which phase do we try to minimise?

A

Phase 2 (it is corrosive, weak, low strength)

19
Q

Properties of Ag3Sn (Gamma)

A
  • hard

- strong

20
Q

Properties of Ag2Hg3 (gamma 1)

A
  • brittle phase
  • intermediate strength
  • small crystals
  • low melting temperature
21
Q

Properties of Sn7Hg (Gamma 2)

A
  • Soft-phase
  • weak low strength
  • high flow
  • corrosion
  • long, blade-like crystals
22
Q

State secondary reaction equation

A

Sn7Hg + Ag-Cu –> Cu6Sn5 + Ag2Hg3

23
Q

What happens if excess mercury is present in the secondary reaction?

A

Then not all of gamma 2 phase is removed

24
Q

Things to think about amalgam?

A
  • conductivity
  • strength magnitude
  • risk of creep?
  • corrosion
  • tarnish (corrosion of top layer only)
  • marginal integrity and microleakage
  • toxicology and biocompatibility
25
Q

Colour of amalgam?

A

lustrous, shiny white

26
Q

Radiopacity of amalgam?

A

> 2mm, aluminium

27
Q

Coefficient of thermal expansion of amalgam?

A

25ppm/degree C

28
Q

Electrical conductivity of amalgam?

A

High

29
Q

Thermal conductivity of amalgam?

A

High

30
Q

What is corrosion?

A

metal reacting with oxygen to form an oxide degrading the surface

31
Q

What is creep?

A

when you apply a force how much does it tilt (could affect marginal seal leading to leakage and recurrent caries)

32
Q

Equation when corroded?

A

Sn8Hg (+ h20 from saliva) –> Hg + SnO2 + Sn(OH)6

33
Q

Harms of corrosion?

A

releases free mercury

34
Q

How can we prevent corrosion?

A

Using high-grade Cu amalgam, eutectic spheres make the material safer as well as stronger

35
Q

What is the difference between using high-grade Cu amalgam and low grade in secondary reaction?

A

Low grade leaves lots of gamma phase 2 whereas high grade there is barely any G2 only G1 which is much stronger and safer

36
Q

What is blended amalgam made of?

A

2 parts conventional alloy + 1 part Ag-Cu eutectic spheres

37
Q

Why should you use cavity varnish when applying amalgam?

A

improves marginal seal

38
Q

why should you have moisture control when applying amalgam?

A

zinc reacts with water releasing hydrogen ions that cause delayed expansion

39
Q

Why should you carve the amalgam restoration?

A
  • removes the mercury rich surface layer

- rebuilds the anatomy of the tooth

40
Q

Why should you polish the amalgam restoration?

A
  • gives lustrous surface

- better corrosion resistance

41
Q

How is mercury toxicity possible?

A
  • Direct contact with mercury
  • removing old restorations
  • mercury hypersensitivity
42
Q

Why has there been a decline in the use of amalgam?

A
  1. Environmental concerns

2. Aesthetic issues

43
Q

Environmental risks of using amalgam?

A
  1. Recycling/disposal of amalgam
  2. Mercury Spillage
  3. Residual mercury left in capsules

Sympsoiums yr2 (27 decks)

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