Amalgam Flashcards
What is dental amalgam?
Alloy formed by the reaction of
Mercury (liquid)
Sliver, tin, copper and other metals (powder)
What are the biggest metal components in amalgam?
Sliver
Tin
What are the possible particle types of amalgam? And how are they made?
Lathe cut
-coarse, medium, fine
-formed by filing ingots
Spherical, spheroidal
-range of particle sizes
-formed by spraying molten metal into inert atmosphere
What is the gamma phase of amalgam and what is it composed of?
Good strength and corrosion resistance
Made out of sliver and tin
What is the gamme 1 phase?
Good corrosive resistance
silver and mercury
stronger than gamma 2 but weaker than gamma
What is the gamma 2 phase?
Weak and poor corrosive resistance,
tin and mercury
(copper is added to counteract it)
Why was zinc removed?
Interaction of zinc with water in saliva/blood forms hydrogen bubbles and creates a pressure build up causing expansion
Downward pressure causes pulpal pain
Why is copper present?
increases strength & hardness
eliminates gamma 2 phase
What method is used to make amalgam?
trituration
What are the advantages of spherical particles?
- less Hg required
- higher tensile strength
- higher early compressive strength
- better packing and density
What are the mechanical properties of amalgam?
- Strength
– generally consider compressive but others important
– early (1hr) - Traditional materials, poor(ish)
– late (> 24hrs) - OK - Abrasion Resistance
– high, suitable for posterior teeth – too high for deciduous - Creep
– amalgam visco-elastic
– high in traditional materials
– affects marginal integrity
NB also marginal integrity depends on: * cavity design
What are the factors that could decrease strength?
- undermixing
- too high Hg content after condensation
- too low condensation pressure
- slow rate of packing
– increments do not bond - corrosion
What is creep?
When a material experiences low-level stress levels (ie below elastic limit stress) which are applied repeatedly over a prolonged time period, it may change shape, resulting in PERMANENT DEFORMATION
What can creep cause?
as the amalgam changes shape and the edges of the cavity protrude, the margins become vulnerable to fracture
What is the biocompatibility concerns about amalgam?
concern about mercury toxicity
“Although mercury is released from dental amalgams the quantities released are very small and do not cause verifiable effects on human beings.
While the current evidence supports the concept that existing dental restorative materials are safe, it must be recognised that the supporting data are incomplete.”
