Amalgam Flashcards
Dental Amalgam is an alloy formed by the reaction of
-mercury (liquid)
-silver, tin, copper & other metals (powder)
What are the metals within amalgam
Ag (silver) 70%
Sn (tin) 25%
Cu (copper) 3%
Zn (zinc) 1%
Hg (merury) 1%
What does copper do
Increases strength and hardness
How are lathe cut particles formed
By filling ingots
What are the types of particles
Lathe cut
Sperical, speroidal
How are spherical particles formed
By spraying molten metal into inhert atmosphere
What is the amalgam setting reaction
Ag3Sn + Hg ——-> Ag3Sn + Ag2Hg3 + Sn7Hg9
What forms the amalgam matrix
g1 and g2
(Ag2Hg3) and (Sn7Hg9)
What is the composition of Gamma, Gamma 1 and Gamma 2
g good strength & corrosion resistance
g1 good corrosion resistance
g2 weak and poor corrosion resistance
What is the gamma phase
(Ag3Sn)
How many phases does amalgam have
3
What property does zinc have in amalgam
Oxidising agent
How does zinc interact with saliva and blood
interaction of zinc with saliva / blood -
Zn + H2O ZnO + H2
What do the bubbles of H2 formed within amalgam cause
pressure build up causes expansion
downward pressure cause pulpal pain
upward - restoration sitting proud of surface
What are the advantages of spherical particles
less Hg required
higher tensile strength
higher early compressive strength
less sensitive to condensation
easier to carve
Name 5 amalgam properties
Strength
Creep
Thermal expansion
Radioplaque
Not Anticariogenic
Thermal conductivity
Rigidity
What factors can decrease the strength of amalgam
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 FLOW, resulting in PERMANENT DEFORMATION
Why does amalgam experience creep
Visco-elastic material
What do the properties thermal expansion, thermal conductivity and thermal diffusivity mean for amalgam fillings
Thermal expansion - x 3 of tooth
Thermal Conductivity – high, may need to use liner / varnish in deep cavities
Thermal diffusivity – high, so when a transient thermal stimuli is applied (eg drinking tea) amalgam’s temperature rises quickly
What is copper enriched amalgam
Doesnt contain the g2 phase, contains >6% copper
What are the advantages amd disadvantages of amalgam
Advantages
strong
hard
durable
radiopaque
user friendly
Disadvantages
corrosion
leakage - does not bond
poor aesthetics
mercury:
- perceived toxicity
- environmental impact
Which amalgam has the least creep
Copper single composition
Which amalgam has the greastest creep values
Traditional lathe
Rate amalgam best - worst
Copper single
Copper dispersion
Traditional spherical
Traditional Lathe
What are the benefits of copper enriched
Higher early strength
Less creep
Higher corrosion resistance
Increased durability of margins
What is the setting reaction of single composition copper amalgam
Ag-Sn-Cu + Hg ——> Ag-Sn-Cu + g1 + Cu6Sn5
What does the first stage of the Dispersion Modified Setting Reaction produce
Gamma, Gamma 1 and Gamma 2
What is the second phase of the Dispersion Modified
Setting Reaction
g2 + Ag-Cu ——> Cu6Sn5 + g1
(takes several days)
What is fully consumed within the Dispersion Modified
Setting Reaction
Gamma 2
Why is the copper enriched amalgam setting reactions better
NO G2 PRODUCED
(all used up in dispersion)
Why is gamma 2 not wanted
Most prone to corrosion
