Amalgam
No description yet. This curated deck is ready for daily study.
Card preview (24)
What is the composition of amalgam
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 property 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