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Dental Materials > Amalgam 2 > Flashcards

Amalgam 2 Flashcards

1
Q

Allot composition affects durability. There have been … controlled clinical trials.
On who?

A
  • 14
  • class 1 and 2, 5-15 year follow up, 3119 restorations
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2
Q

Explain the clinical trials on durability of alloys

A
  • divided into 4 groups
  • zinc (free or containing)
  • copper (conventional or high)
  • failures reason assessed as related to restoration, process or patient
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3
Q

Results of durability of alloy trials

A
  • 481 failed restorations
  • 77% failed due to restoration
  • 80% due to fracture of amalgam
  • conventional zinc-free has shortest
  • high copper zinc-containing longest
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4
Q

Mechanical properties of amalgam

A
  • hard
  • rigid
  • brittle
  • strong in compression, weak in tension
  • low flexural strength
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5
Q

How is strength developed in amalgam over time?
What to tell patient?

A
  • slowly
  • danger of early fracture so patients warned
  • alloy powder side influences setting rate - smaller particles leads to faster strength development
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6
Q

Key features of cavity design and placement of amalgam

A
  • sufficient bulk
  • avoidance of thin amalgam sections
  • final mercury content of less than 50%
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7
Q

What variables can be manipulated with amalgam?

A
  • proportioning/mixing
  • mercury to alloy ratio
  • trituration - mixing by grinding
  • mercury hygeine
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8
Q

Why is proportions and mixing
manipulated?

A
  • ease
  • reproducibility
  • safety
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9
Q

How can the mercury alloy ratio be manipulated?

A
  • enough mercury for fluid mix
  • less than 50% mercury for good properties
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10
Q

Why is trituration manipulated?

A
  • ease
  • reproducibility
  • safety
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11
Q

Why is mercury hygeine manipulated?

A
  • to protect patient
  • and dental personnel
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12
Q

4 stages of manipulation of amalgam

A
  • proportioning and mixing
  • condensing
  • carving
  • polishing
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13
Q

Difference between traditional and modern proportioning

A
  • traditionally done by dentist or assistant
  • now encapsulated products
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14
Q

Final strength of amalgam depends on …

A
  • keeping as much gamma as possible
  • reducing mercury concentration to 40-45% in set material
  • mercury to alloy ratio is important
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15
Q

Explain traditional trituration

A
  • done by hand
  • mortar/pestle
  • required a wet mix (8:5 mercury to alloy)
  • took 40 seconds
  • resulted in excess mercury - and weakness therefore
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16
Q

What is trituration?

A

mixing by grinding

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17
Q

How is trituration done now?

A
  • an amalgamator
  • requires less mercury 1:1 if possible
  • mechanical for 8-15 secs
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18
Q

Explain condensation stage

A
  • transfer mixed amalgam to cavity
  • build up increments
  • condense with plugger/condenser
  • condense while plastic soon after trituration - don’t delay
19
Q

What does condensation allow to happen?

A
  • adapt to cavity form
  • binds together increments
  • reduces porosity
20
Q

Condensation pressure affects what?

A

final amalgam strength

21
Q

Condensation reduces …
How?

A
  • final mercury content
  • causes mercury to rise to the surface
22
Q

Effect of Lathe cut particles in condensation

A
  • resist flow due to friction and interference
  • require high force and high rate of application
  • gives good feedback to dentist
23
Q

Effect of spherical particles in condensation

A
  • easily flow passed each other
  • requires lower forces and wider pluggers
24
Q

How do a mixture of particles affect condensation?

A
  • faster setting times of small particles
  • good feedback from larger particles
25
Q

Explain carving of amalgam

A
  • always over fill cavity in condensation
  • remove mercury rich layer with carver (sharp steel or stellite)
26
Q

Why don’t we carve when it’s too soft?

A
  • drags out material
  • drags are thin sections which are weak
27
Q

Why don’t we carve when it’s too hard?

A
  • can’t carve it
  • material is brittle and fractures
28
Q

How does particle size influence carving?

A
  • fine grain easier than coarse
  • spherical amalgams easier to carve
29
Q

Explain polishing process

A
  • final stage
  • ideally when setting is complete - next visit
  • use abrasive suspended in fluid
  • zinc oxide in alcohol, pumice in glycerine, chalk
30
Q

Why do we polish amalgam?

A
  • improve appearance of restoration
  • prevent accumulation of food and micro-organisms
  • improves corrosion resistance - corrosion occurs rapidly in crevices and polishing creates a ‘Beilby layer’ to form an amorphous layer with good corrosion resistance
31
Q

4 features of the amalgam interface with tooth

A
  • no adhesion
  • possible leakage
  • thermal diffusivity
  • coefficient of thermal expansion
32
Q

Why is there no amalgam adhesion at tooth interface?

A
  • retention by cavity design of undercuts
  • destroys sound tooth
  • replacement destroys more tooth
33
Q

Why is leakage possible at amalgam interface with tooth?

A
  • corrosion products can seal margins - in vitro evidence
  • bonding agents can be used - not widely though
34
Q

How does amalgam interface have thermal diffusivity?

A
  • pulp sensitive to temp change
  • needs lining
35
Q

How does amalgam interface with tooth have coefficient of thermal expansion?

A
  • mismatch with tooth
  • ‘percolation’ is possible
36
Q

Where do concerns about amalgam come from?

A
  • mercury content
  • rival business claims
  • public health scares
37
Q

Sources of mercury

A
  • propotioning amalgam - modern capsules
  • trituration - modern amalgamators
  • residual mercury in fillings - condensation
  • corrosion - gamma 2 free amalgams now used
38
Q

Where have bans on amalgam?

A
  • Norway, Sweden and Denmark have bans on import, transport and use of mercury compounds
39
Q

What did Jones find about amalgam?

A
  • no conclusive evidence shows link between amalgam and neurological disorders and impaired kidney function
  • same with animals
40
Q

Potential environmental sources of mercury

A
  • over 50% from natural sources
  • 42% from fossil fuels burning
  • daily intake from 10 amalgam surfaces in mouth - 2% of WHO levels
41
Q

Explain the Minimata Tragedy

A
  • 1952 Japanese chemical industry booms
  • fish found floating in Minamata bay
  • domestic cats behaving bizarrely - neurological disorders and cat suicides
  • humans affected sporadically, no warning, death/paralysis/maiming
  • linked to high mercury in fish, mainly shellfish
  • 2955 contracted the disease and 1784 have died
42
Q

Mercury ban in Norway

A
  • fish industry major employer
  • german u-boat of 65,000 of mercury on ocean floor
  • acid-rain gave env mercury - similar to other places
  • env concerns lead to attempt to reduce mercury use
  • not based on amalgams
43
Q

Sweden and Denmark mercury ban

A
  • Sweden largest employers are automobile and battery manufacturers - large mercury use
  • amalgam not based on health risk from amalgam
44
Q

What is the Minimata Convention?

A
  • global drive to reduce mercury use (not just amalgam)
  • no amalgam use in pregnant women, under 16s, likely phase out of all amalgam use

Dental Materials (17 decks)

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