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basic oral and dental care > dental amalgams > Flashcards

dental amalgams Flashcards

1
Q

What is dental amalgam?

A

Silver and shiny
Metal alloy powder (Ag3Sn) and liquid (Hg) capsule- safety
Conducts heat
Cheap

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2
Q

What are the two types of amalgams?

A

Conventional

High copper content (non gamma 2)

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3
Q

What is the composition of conventional amalgams?

A

Gamma phase-
~Silver, Ag 67-74%
~Tin, Sn 25-27%

~Copper, Cu ~6%
~Zinc, Zn ~2%

=alloy powder

+ triple distilled mercury, Hg
=liquid

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4
Q

What is the gamma phase?

A

Alloy

Eg. Ag3S, intermetallic compound, very narrow compositional range=3rd pure phase of Ag and Sn

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5
Q

How do you work out the type of alloy?

A

Atomic size
Covalency
Structure

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6
Q

What are the three types of alloy?

A

substitutional solid solution
interstitial solid solution
intermetallic compound

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7
Q

What do the size and shape of the powder particles influence?

A

Handling
Setting reactions
Final properties

Lathe cut (course/fine grains) OR spherical

Spherical handled easier
Fine grain sets faster

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8
Q

What is the setting reaction?

A

Ag3Sn + Hg—> Ag3Sn + Ag2Hg3 + Sn7-8Hg

Solid + liquid—> 3 solids

Alloy + triple distilled mercury—> unreacted alloy + silver mercury phase (gamma 1) + tin mercury phase (gamma 2)

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9
Q

What does the amalgam look like on a micrograph?

A

A. Outer layer of alloy particles dissolve in mercury
B. Gamma 1 phases form
C. Gamma 2 phases form (less)
D. Unreacted gamma alloy particles in a matrix of gamma 1 and 2 matrix

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10
Q

Why are amalgams placed?

A 
Primary caries
Secondary caries
Poor margin
Restoration fracture
Tooth fracture 
Other
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11
Q

Why are amalgams replaced?

A

Tooth fracture
Recurrent caries
Gross amalgam fracture
Marginal breakdown

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12
Q

Why might the tooth fracture?

A 
Undermined enamel (done via prep)
Weakened tooth structure (aim for minimal removal of tooth)
Residual caries (spreads and undermines cusp) + inflam of pulp
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13
Q

Why might recurrent caries occur?

A

Amalgam adults- 72%
Amalgam kids- 56%
Composites- 43%
~1985

Contamination
Poor matrix techniques (overhangs)
Poor condensation (porosity and excess Hg- reduced strength) (poor margins)

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14
Q

Why might there be a gross amalgam fracture?

A 
Shallow prep
Pressure points (sharp internal angles)- stress concs 
Not well mechanically retained proximally (reduced w grooves)
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15
Q

What is the tensile strength of amalgams?

A

69 MPa

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16
Q

Why might there be marginal breakdown?

A

Incorrect cavo-surface angles (esp acute)
Delayed expansion (if site not dry, zinc reacts w saliva to form ZnO and H2 gas- bubbles expand, amalgam expands, pressure on pulp)
Over/underfilling
Over carving
Creep and corrosion (metal dislocates and degrades)

17
Q

What are problems with amalgams?

A 
Non-adhesive
Not aesthetic 
Not strong/tough
Susceptible to creep and corrosion
Biocompatibility
18
Q

What is the benefit of having a stronger amalgam?

A

Preparing cavity simpler

Remove less tooth structure

19
Q

What are the tensile strengths?

A

Amalgam- 60MPa
Gamma- 170MPa
Gamma-1- 30MPa
Gamma-2- 20MPa

Would be stronger if we got rid of gamma-2

20
Q

What are lathe cut particles?

A

Machined from solid ingot
Graded chippings
Highly reactive w/o prior heating

21
Q

What are spherical alloys?

A

Reach full strength more quickly
Easier to condense
Easier to carve and polish
Lower mercury content

22
Q

What is admix?

A

Dispersed phase amalgams
Addition of Cu

Lathe cut + spherical= admix

AgSn alloy + AgCu alloy= AgSn +AgCu alloy

23
Q

What is the dispersed phase amalgam modified reaction?

A

Gamma + mercury + AgCu—> gamma + gamma-1 + gamma-2

—> (gamma-2 + AgCu)—> gamma + Cu6Sn5 + gamma-1

24
Q

What is the single phase high copper content formulation?

A

AgSnCu + Hg—> gamma-1 + (AgSnCu) + Cu6Sn5

Cu>12%

CuSn can be Cu3Sn or Cu6Sn5 depending on precise starting composition

25
Q

What is the microstructure of the high copper amalgam?

A

Gamma
Gamma-1
Unreacted AgCu
CuSn phases (Cu3Sn, Cu6Sn5)

26
Q

How corrosive is traditional amalgam?

A

Cathodic-
~Gamma -0.10V
~Gamma-1 +0.15V

Anodic-
~Gamma-2 -0.70V

Galvanic cell-
Electrochemical difference in electrolyte so anode metal corrodes

So if we get rid of gamma-2- less corrosion

27
Q

What’s re the benefits of high copper amalgams?

A 
Reach full strength more quickly
Easier to condense/carve/polish
Lower mercury content
Higher strength
Better resistance to corrosion
28
Q

What are dental amalgam variations?

A

Conventional

  • lathe cut Ag3Sn
  • spherical Ag3Sn

High Cu dispersed phase

  • Lathe cut Ag3Sn + spherical AgCu
  • Lathe cut AgSnCu + spherical AgSnCu

High Cu single phase

  • Spherical AgSnCu
  • Lathe cut AgSnCu
29
Q

What are the potential symptoms and hazards of mercury exposure?

A 
Respiratory failure
Kidney impairment
Cognitive disturbances 
Reduced visuoperceptual and constructional skills
Memory loss
Hypertension
Headaches
30
Q

What are potential sources of Hg contamination?

A

Spills
Leaky dispensers or capsules
Removing or polishing amalgams
Sterilising mercury contaminated instruments

31
Q

How should mercury contamination be avoided?

A
  • Use pre-capsulated alloys
  • Avoid direct skin contact and wear mask
  • Use high vol evacuation when finishing or removing amalgams
  • Store bulk mercury in unbreakable containers
  • Store amalgam scraps under radiographic fixer solution
  • Dispose contaminated items in sealed bags
  • Report and clean up spilled mercury immediately using clean up kit
  • Wear professional clothing only in dental surgery
  • provide proper ventilation
  • monitor mercury vapour levels in dental surgery
  • monitor personnel eg. Mercury urine level
  • use proper work area design
  • use an amalgamator with a cover
  • treat w respect

basic oral and dental care (49 decks)

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