Clinical aspects of Amalgam Flashcards
what components make up amalgam and dental amalgams
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
Describe the structure of amalgam capsules
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
Describe the different types of alloy powder (particle shape)
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
Describe alloy powder dissolving in liquid mercury
- 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
what are the 3 possible combinations of the dissolved metals
what is gamma 2 Sn7Hg responsible for
corrosion - plaque retentive factor
creep - deformation under load
decrease in strength
how do corrosion products seal the cavity
- after amalgam is paced int he cavity, the corrosion products seal gap to bond amalgam restoration to dentine
what is the benefit of adding copper to dental amalgam
to reduce gamma 2
better material
admixed
- adds strength
what does adding zinc do to amalgam
- 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
what is the ideal powder; liquid ratio of amalgam
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
describe 7 goods things about amalgam
- good compressive strength
- good wear resistance
- kind to opposing teeth
- easy to use
- chemical set
- cheap
- radioopaque
describe the disadvantages of amalgam
- non adhesive
weak in thin sections
thermal conductor
unaesthetic- dentine could discolour - plaque retentive factors if overhangs
occasional lichenoid- type reactions
what properties should our amalgam cavities have
- undercut
- deeper than 2mm
- pits and grooves
- cavosurface angle -
what are clinical indications of amalgams
- 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
describe retention and resistance
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
what was older technique of using pins in amalgam
- 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
How is amalgam bonded?
- 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
why is polishing important after placing a amalgam restoration
- 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
Is amalgam safe to use
- 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
how is mercury poisonous?
- 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
what is the minimal convention
- 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
what is the evidence of risk from dental amalgam
- no evidence of risk from mercury in amalgam to patients or dental staff
problem occurs when mercury enters the environment
what should be done in clinical skills lab when suing amalgam
- report mercury spills
- put empty capsules and waste amalgam in the receptacles provided
- clean the heads into the designated sink - has separator on it
Descirebt he different regulations of amalgam
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
