2. Amalgam Flashcards
- What are five reasons supporting the use of amalgam in restorations?
- Inexpensive
- Ease of use
- Proven track record (>100 years)
- Familiarity
- Resin-free (results in less allergies than composite)
- What are two reasons as to why Copper (Cu) is a component of amalgam?
- Ties up tin (reducing gamma-2 formation)
2. Reduces creep (less marginal deterioration)
- What is one reason as to why Zinc (Zn) is using during the manufacture of amalgam?
What downside is there to the use of Zinc?
It is a deoxidizer - decreases oxidation of other elements (acts as a sacrificial anode)
Downside - can result in delayed expansion
- The basic composition of amalgam consists of “filler (bricks)” and a “matrix”. What two chemicals comprise the “matrix”?
- Ag2Hg3 - Gamma 1 (acting as the cement)
2. Sn8Hg - Gamma 2 (forms voids and is the weakest part of an amalgam)
- Describe the alloy structure of single composition high-copper alloys
Gamma (γ) sphere with epsilon (ε) coating
γ: Ag3Sn
ε: Cu3Sn
- In single composition high-copper alloys, what elements will dissolve in mercury (Hg)?
(Reminder: Gamma (γ) sphere with epsilon (ε) coating
γ: Ag3Sn
ε: Cu3Sn)
Ag and Sn both dissolve in Hg
- Write the chemical reaction that single composition high-copper alloys undergo?
Ag3Sn (γ) + Cu3Sn (ε) + Hg ->
Ag3Sn (γ) + Cu3Sn (ε) + Ag2Hg3 (γ1) + Cu6Sn5 (ŋ)
Note: As Ag and Sn dissolve out of the alloys and into the mercury solution, both (γ1) and (ŋ) are formed. This is what prevents creep. Notice also that gamma-2 (Sn8Hg) is not being made because it is being tied up in the formation of (ŋ) Cu6Sn5.
- What is one difference between Single Composition Spherical amalgam (SCS) with Single Compositio Lathe-cut amalgam (SCL) in regards to condensation force and size of condenser used?
SCS requires less condensation force, but requires the use of a larger condenser
- Do high-copper amalgams undergo dimensional change (contraction)?
Yes, most high-copper amalgams undergo a net contraction resulting in a marginal gap
- What accounts for the post-operative sensitivity that may be present after an amalgam restoration? How is this issue reduced over the life of the amalgam restoration?
Post-Op sensitivity: Due to formation of marginal gap which results in initial leakage
Over the life of the amalgam corrosion will decrease the marginal gap
- What three factors can lead to dimensional change (marginal gap) in amalgam restorations?
- Alloys
- Condensation
- Trituration
- Type of alloy used - spherical alloys have more contraction due to less mercury
- Condensation technique (greater condensation = higher contraction)
- Trituration time (overtrituration = higher contraction)
- Do amalgams have higher compressive or tensile strength?
Compressive»_space; Tensile
Thin sections of amalgam are weak and can fracture
- What are the two effects that corrosion can have on an amalgam restoration?
- Reduction in strength
- Margins will become better sealed - time frame will change based on whether low copper (6 months /w gamma-2 phase) or high copper (6-24 months w/ eta phase (Cu6Sn5))
- What does amalgam creep correlate with?
What percentage of copper in high-copper amalgams is required in order to prevent amalgam creep?
Marginal breakdown
12% Copper will prevent the gamma-2 phase and reduce the creep rate
- Overtrituration
- Signs of overtrituration?
- How does overtrituration affect working/setting time?
- How does overtrituration affect setting contraction?
Signs: “hot” mix - sticks to capsule
Decreases working/setting time
Slight increase in setting contraction
