Amalgam Flashcards
(80 cards)
Dental amalgam is an <i>alloy</i>. It is formed by the reaction of what materials?
- Mercury (liquid)
- Silver, tin, copper and other metals (powder)
What is an alloy?
- A material made from the mixing of 2 or more metals
What are the 2 different ways in which you can classify amalgam?
- By composition
- By particle size and shape
When classifying amalgams by composition. What are the 2 different possible compositions of amalgam?
- Traditional
- Copper enriched
Why do we sometimes classify amalgams into particle shape and size?
- As this affects the handling and final properties
What is the composition of amalgam?
- Ag (silver) = 70%
- Sn (Tin) = 25%
- Cu (Copper) = 3%
- Zn (Zinc) = 1%
- Hg (Mercury) = 1%
What are the functions of silver and tin the amalgam?
- This is am intermetallic compound which reacts with Hg liquid to form amalgam - this is the gamma phase
What is the function of copper in the amalgam?
- Increases strength and hardness (ensures that the material lasts longer)
What is the function of zinc in the amalgam?
- Scavenger during production - preferentially oxidise s and slag formed/removed - some zinc free
(Zn oxidises to prevent the other materials from oxidising)
What is special about ‘pre-amalgamated’ alloys?
- They react faster
What makes the liquid Hg in amalgam very pure?
- It is triple distilled
What is the function of liquid Hg in amalgam?
- Reacts with other metals
What is a lathe cut particle and how is it formed?
- Coarse, medium, fine
- Like a shaving (creates all sorts of fragments of irregular shape)
- Formed by filing ingots
What is an ingot?
- A loose term applied to any mass of material specifically cast from a molten state of known composition, weight, shape and physical dimension
What is a spherical/spheroidal particle and how is it formed?
- Range of particle sizes
- Formed by spraying molten metal into the inert atmosphere and so they produce globules as they hit the surface underneath
What is the setting reaction of amalgam?
- Ag3Sn + Hg -> Ag3Sn + Ag2Hg3 + Sn7Hg9
- Powder + liquid -> unreacted particles + amalgam matrix
What properties does gamma in the set structure of amalgam have? (2 points)
- Good strength
- Good corrosion resistance
What property does gamma 1 in the set structure of amalgam have?
- Good corrosion resistance
What properties does gamma 2 in the set structure of amalgam have?
Weak and poor corrosion resistance
What do voids in the set structure of amalgam cause?
- Decreases strength and increases corrosion
What is the mean tensile strength of the gamma component of amalgam?
170MPa
What is the mean tensile strength of the gamma-1 component of amalgam?
30MPa
What is the mean tensile strength of the gamma-2 component of amalgam?
20MPa
What is the mean tensile strength of amalgam?
60MPa