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CSA > Clinical aspects of Amalgam > Flashcards

Clinical aspects of Amalgam Flashcards

1
Q

what components make up amalgam and dental amalgams

A

Amalgam - ANY alloy of mercury with another metal or other metals
Dental Amalgams - essentially an alloy of silver, mercury and tin, with some other metals added to modify properties
- alloy powder mixed with liquid mercury forms a paste which is mouldable

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2
Q

Describe the structure of amalgam capsules

A

All amalgams comes in sealed caps
Liquid mercury at one end and alloy in other
Push them in and it breaks membrane
High speed amalgamator mixes it

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3
Q

Describe the different types of alloy powder (particle shape)

A

Spherical - made by spraying molten metal into a fine mist
softer and more flowable
Lathe cut- made by creating an ingot of alloy and grinding down to a powder
Less flowable, good for building up large amounts of missing tooth structure

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4
Q

Describe alloy powder dissolving in liquid mercury

A
  • mixture of spherical and lathe cut
  • powder and liquid mercury meet, the mercury surrounds powder particles and dissolves them
    Powder particles contain silver and tin mainly
  • silver and tin goes out into the solutions
  • 3 possible combinations of dissolved metal can accur
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5
Q

what are the 3 possible combinations of the dissolved metals

A
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6
Q

what is gamma 2 Sn7Hg responsible for

A

corrosion - plaque retentive factor
creep - deformation under load
decrease in strength

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7
Q

how do corrosion products seal the cavity

A
  • after amalgam is paced int he cavity, the corrosion products seal gap to bond amalgam restoration to dentine
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8
Q

what is the benefit of adding copper to dental amalgam

A

to reduce gamma 2
better material
admixed
- adds strength

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9
Q

what does adding zinc do to amalgam

A
  • zinc is a scavenger that preferentially oxidises when metals are heated and prevents the others forming oxides
  • to reduce the amount of zinc, could be heated in an inert atmosphere
  • no benefits to the material
  • added by some manufacturers to prevent silver form oxidising during manufacture of the powder
  • not needed if powder can be manufactured in a vacuum
  • its presence can cause large expansion of material as it sets - leads to crakc within tooth
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10
Q

what is the ideal powder; liquid ratio of amalgam

A

50% mercury 50 % alloy powder
however trying to mix powder with < 50 % s=is didfuclt as mix is too dry so it can be hard to pack into cavity
- therefore more than 50% MERCRURY ADDED TO AMKE IT WORKABLE
- excess mercury is drawn to top but carved away

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11
Q

describe 7 goods things about amalgam

A
  • good compressive strength
  • good wear resistance
  • kind to opposing teeth
  • easy to use
  • chemical set
  • cheap
  • radioopaque
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12
Q

describe the disadvantages of amalgam

A
  • non adhesive
    weak in thin sections
    thermal conductor
    unaesthetic- dentine could discolour
  • plaque retentive factors if overhangs
    occasional lichenoid- type reactions
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13
Q

what properties should our amalgam cavities have

A
  • undercut
  • deeper than 2mm
  • pits and grooves
  • cavosurface angle -
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14
Q

what are clinical indications of amalgams

A
  • larger cavities affecting posterior teeth
  • where heavy occlusal forces are encoutnered
  • where aesthetics are not important
  • patients with a high caries rate
  • posterior restoration that extend subgingivally
  • building up broken down teeth prior to crowning
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15
Q

describe retention and resistance

A

Retention - prevention of being pulled out of the cavity vertically
macromechanical
undercuts are sufficient for occlusal and small approximal
Resistance- prevention of being dislodged under load
dovetail(keyhole)
cavosurface angle

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16
Q

what was older technique of using pins in amalgam

A
  • create wall by putting 1/2 pins into tooth
  • helps with vertical direction
  • put the pins can go into dentine
    into pulp - death of tooth
17
Q

How is amalgam bonded?

A
  • adhesive system similar to use in composite
    active substance MDP/4-META form a hybrid layer with dentine and a chemical bond to amalgam
  • difunctional monomer
    long chemical names
    form chemical bonds of the tooth
  • alternatively wet uncured RMGIC placed in the base of cavity can have amalgam packed directly on top
18
Q

why is polishing important after placing a amalgam restoration

A
  • less plaque retention
  • more comfort for the patient
  • polishing will not improve the life expectancy of the restoration
  • heat generated may be harmful to the pulp
19
Q

Is amalgam safe to use

A
  • amalgam is approx 50% mercury
  • mercury vapour is highly toxic
    mercury vapour is ingested whenever amalgams are mixed, placed or removed
  • Mercury vapour is released from amalgam filling during chewing and toothbrush
  • it had never been convincingly shown that the negligible levels of mercury entering the body from amalgam fillings have any impact on general health
20
Q

how is mercury poisonous?

A
  • when mercury enters the environment it can be converted by bacteria to methyl mercury in fresh and salt water
  • methyl mercury is highly poisonous

Governments such as Sweden and Germany that have banned amalgam have done so on environmental grounds rather than for health issues in its use

21
Q
A
21
Q

what is the minimal convention

A
  • bane on mercury contianing products and ‘phase down’ of amalgam by 2020
    call for a cease to teaching amalgam by 2015
    little agreement over protocols between schools
  • like it or not, composite will become the widely used type of materaol in the restoration of posterior teeth
22
Q

what is the evidence of risk from dental amalgam

A
  • no evidence of risk from mercury in amalgam to patients or dental staff
    problem occurs when mercury enters the environment
23
Q

what should be done in clinical skills lab when suing amalgam

A
  • report mercury spills
  • put empty capsules and waste amalgam in the receptacles provided
  • clean the heads into the designated sink - has separator on it
24
Q

Descirebt he different regulations of amalgam

A

Jan 2019- dental amalgam shall only be used int he pre-dosed encapsulated form
July 2018- dental amalgam should not eb used for treatment of deciduous teeth of children under 15 , pregnant or breastfeeding women except when deemed strictly necessary by the dental practitioner based on the specific medical needs of the patient
1 July 2019- measures to phase down the use of amalgam
January 2019 = requirement for dental facilities to be equipped with an amalgam separator

CSA (32 decks)

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