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Applied Dental materials > Dental amalgam > Flashcards

Dental amalgam Flashcards

1
Q

what is dental amalgam a product of?

A

amalgamation :

alloy + mercury react to form silvery hard grey mass

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2
Q

why is it not increasingly demanded from the public?

A

performs better but has poor aesthetics

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3
Q

why is the use of dental amalgam declining?

A
  • development of viable alternatives

- concerns on safety and environmental pollution

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4
Q

what are the two compositions of dental amalgam?

A
  • conventional (products pre 1996)

- higher copper (post 1986)

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5
Q

what was development of amalgam stimulated by?

A

better understanding of structure properly relationships

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6
Q

what is the conventional composition of amalgam?

A
  • 65% Ag
  • 29% Sn
  • 6% Cu
  • 2% Zn
  • 3% Hg
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7
Q

what is the typical high copper composition of amalgam?

A
  • 40% Ag
  • 32% Sn
  • 30% Cu
  • 2% Zn
  • 3% Hg
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8
Q

what are the variations in alloy morphology?

A
  • lathe cute

- sperhical

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9
Q

what gamma phases is wanted and which is not wanted?

A

wanted - phase 1

not wanted - phase 2

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10
Q

Describe the dental amalgam setting reaction.

A
  • preponderance of Ag3Sn (undergoes setting reaction)
  • Cu has strengthening effect on amalgam
  • Zn acts as scavenger in alloy production (may eliminate if manufacture in inert atmosphere
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11
Q

what is mixing termed?

A

trituration

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12
Q

Describe the setting reaction and dimensional changes.

A

Dimensional changes :

  • 30 mins small shrinkage (Hg diffuses into alloy)
  • 30-60 mins - expansion due to crystallisation
  • overall effect is either net expansion /contraction
  • ISO limit +/- 0.1% expansion/contraction
  • manipulative variables help limit
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13
Q

why is moisture controlled during setting reaction?

A

when Zn combines with H20 , H2 gas is produced

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14
Q

how long is the setting reaction from placement to function?

A

15-20 minutes

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15
Q

how long is the setting reaction for final strength?

A

24 hours

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16
Q

How does compressive strength relate to tensile and transverse strength?

A

compressive strength is greater than tensile and transverse

17
Q

what is strength proportional to?

A

Mercury (Hg) content

-optimum if Hg 44-48%

18
Q

Describe creep properties.

A

Plastic deformation under load :
clinically flows manifesting as protrusions at restoration margins
-fracture off producing ditching
-responsible: gamma 2 largely, but not exclusively
-corrosion of the alloy exacerbates (releases Hg in marginal crevice ) –> localised expansion of amalgam

19
Q

Describe corrosion properties.

A

Electrochemical interactions of different alloy phases with salvia as electrolyte :

  • gamma 2 anode
  • gamma 2 breaks down to Sn and Hg ( Hg remains free and is ingested)
  • ADVANTAGE- corrosion products provide marginal seal
  • in high copper phase undergoing most corrosion is CU-Sn (does not corrode as much)
20
Q

Describe thermal properties.

A
  • metal has high thermal diffusivity
  • three fold coefficient of thermal expansion of dentine
  • in reality not a problem due to transient nature of functionally encountered thermal stimuli
21
Q

Describe biological properties.

A

Hg compounds know to be toxic to CNS:

-risk to dental team

22
Q

what risk does dental amalgam have to the patient?

A

-1998 placement and removal of dental amalgam restorations banned by D o H during pregnancy
-no conclusive evidence but perceived elevated risk:
Hg doses high -placement,contouring, removal
-Hg concentrates and crosses placenta (abortion/child abnormalities?)
-high concentration of Hg in urine/blood of those with amalgam restorations

23
Q

what do some reports link dental amalgam to?

A

-multiple sclerosis
-behavioural problems
-psychiastric disturbances
(removals of amalgam restorations claimed to bring about relief of symptoms)

24
Q

What about environmental pollution?

A
  • water of dental unit
  • release of Hg during trituration
  • crematoria
25
Q

Describe manipulative variables

A
  • alloy:Hg ratio
  • range 5:8 to 10:8
  • drier mixes achieved by mechanical mixing
  • packing and condensation removes excess mercury
26
Q

Describe dispensation of dental amalgam.

A
  • weight (most accurate)
  • volume dispensers
  • alloy tablets
  • proportioning and mixing devices
  • now generally manufacturer encapsulated (accurate and most reproducible)
27
Q

what are the manufacturer variables?

A

Particle size of alloy :

  • smaller achieves higher 1 and 24 hour strengths
  • if extremely small : too rapid a set -cannot remove excess Hg by manipulation

Applied Dental materials (5 decks)

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