Final Exam: Amalgams Flashcards
What is an amalgam?
Alloy of mercury with other metal(s)
What do we use amalgam?
- What’s the cost like?
- Easy or difficult to use?
- What’s the proven track record?
- Why do we use it over composite?
- Inexpensive
- Ease of use
- Proven track record: (x) > 100 years
- Resin Free: Less allergies than composite
Basic constituents of amalgam:
COPPER (CU)
– What does it tie up? This helps reduce what kind of formation?
– Copper helps increase what in the amalgam?
– What three things does it reduce?
– If you increase CU, what happens?
– How is CU added to amalgam?
– ties up tin
– reducing gamma-2 formation
– increases strength
– reduces tarnish and corrosion
– reduces creep: deformation under steady pressure
—reduces marginal deterioration
-High copper = much better
Cu added by epsilon coating
Basic constituents of amalgam:
Zinc (Zn)
– Zinc is used in what and help do what in amalgam?
– What kind of anode is it?
- How does it help in providing better clinical performance?
- Zinc, in the presence of low CU allows, what does it do to the amalgam? …. and under what circumstance?
- Zinc is used in manufacturing
- Decreases oxidation of other elements (so no rusting)
- Sacrificial anode
- Zinc is used in manufacturing
- Less marginal breakdown
- Causes delayed expansion with low Cu allows
- If contaminated with moisture during condensation. ( H2O + Zn –> ZnO + H2 )
- Causes delayed expansion with low Cu allows
Basic composition of amalgam: (single composition)
What are the two matrix present in amalgam?
Matrix:
- - Ag2Hg3 called gamma 1
- - cement
- - Sn8Hg called gamma 2
- - Voids, weak, BAD GUY
Single Composition High-Copper Alloys
In High-Copper Alloys:
- What kind of sphere is associated with it? Give formula as well.
- What kind of coating is associate with it? Give formula as well.
- Silver and Tin dissolves in what element?
- Tin has affinity for what?
– Gamma sphere (g) (Ag3Sn)
– epsilon coating (e) (Cu3Sn)
– Ag and Sn dissolve in Hg
(Silver) (tin)
– Tin has affinity for copper
Gamma Epsilon
Ag3Sn + Cu3Sn + Hg -> Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5
Gamma Eta
Single Composition Spherical (SCS)
- Greater or less condensation force?
- What size of condenser would you use with SCS particles?
- What kind of sphere is associated with gamma particles?
- Less condensation force
- Larger condenser
- Gamma particles as 20 micron spheres
Dimensional Change
- Most high-copper amalgams undergo what kind of contraction?
- What do contractions leave?
- Initial leakages causes what type of sensitivity
- Over time, the marginal gap is reduced as a result of what?
- Most high-copper amalgams undergo a net contraction
1) Contraction leaves marginal gap
a) initial leakage
- aa)post-operative sensitivity
- Most high-copper amalgams undergo a net contraction
- Reduced with corrosion over time seals the marginal gap over time
Dimensional Change
The net contraction of amalgam is dependent on three things. What are they?
1) Type of alloy
2) Condensation technique
3) Trituration time
Dimensional Change
- What type of alloy plays a role in the net contraction?
- This type of alloy has MORE contraction due to what reason?
- spherical alloys (have more contraction)
- - More contraction due to LESS MERCURY
When using the condensation technique:
By having a greater condensation, what kind of contraction will you have?
HIGHER contraction
Trituration time:
Overtrituration (of the amalgam) causes what kind of contraction?
Higher contraction
Strength of amalgam:
What two characteristics are used to measure the strength of a particular amalgam?
- In thin sections of amalgam, what’s the strength like and why?
- What to do with caution points on amalgam?
- Higher compressive vs. tensile strength
- Weak in thin sections
- because UNSUPPORTED EDGES FRACTURE (brittle)
- Weak in thin sections
- Wait till the amalgam completely settles before chewing since there will be caution points after amalgam restoration.
Corrosion:
- Corrosion of the treated teeth results to what sort of strength?
- – Corrosion does what to the margins?
- – Using a low copper or high copper amalgam material, corrosion will last for how long?
- What phases accompany with these two copper materials.
- Reduces strength
- Seals margins
* low copper:
- - 6 months
- - SnO2, SnCl
- - gamma-2 phase
- Seals margins
* high copper: - - 6 - 24 months - - SnO2 , SnCl, CuCl - - eta-phase (Cu6Sn5)
What is Creep?
slow deformation of amalgam placed under a constant load.
load less than that necessary to produce fracture
Creep is correlated with what kind of breakdown?
Correlates with MARGINAL breakdown.
The presence of what kind of copper amalgams have creep resistance?
- High-copper amalgams prevent the formation of what type of matrix (aka… what kind of phase)?
- – Requires how much % of Cu in total for prevention of gamma-2 phase
- High-copper amalgams prevent the formation of what type of matrix (aka… what kind of phase)?
- High-Copper amalgams
- Prevention of gamma-2 phase
- (x) > 12%
Creep is present more in which gamma phase?
a lot more in gamma 2 phase
remember that gamma 2 phase matrix….. are that “bad” guys. This will be on test
Trituration:
Name the two types of trituration discussed in class.
- Overtrituration
- - Undertrituration
Overtrituration:
- What kind of mix is associated with an overtrituration mix?
- This mix would result to an increase or decrease working/setting time?
- This mix would result to an increase or decrease in setting contraction?
Overtrituration:
- - “hot” mix: sticks to capsule kinda like a ball after you "centrifuge" it.
- - decreases working / setting time
- - slight increase in setting contraction
In undertrituration, what kind of mix do you get from it?
– Grainy, crumbly mix
Condensation of amalgam:
- Condensation is said to be a continuation of what?
- Condensation packs the amalgam to what?
- Continuation of trituration
- - Adapts amalgam to cavity walls
Condensation of amalgam:
- The process of condensation reduces what in restoration?
- The process of condensation will help eliminate or induce voids?
- The process of condensation will help increase or decrease the strength and serviceability of restoration?
- Reduces residual Hg in restoration (reduces creep)
- Eliminates voids
- Increases strength and serviceability of restoration
Spherical alloys have what kind of condensing force?
Less condensing forces
What kind of copper will corrode faster?
- Low copper corrodes faster (6 months)
- - High copper will still SEAL
Stability:
Do all amalgams contract?
– If there are more contraction, what will happen to the sensitivity?
– What type of alloy (shape) will contract more?
- All amalgam contracts a bit
- More contraction = more sensitivity
- Spherical alloys contract more
