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32 Cards in this Set

  • Front
  • Back
What are main components of amalgam?
Silver 41-61%
Tin 28-31%
Copper 12-27%
What are the 6 metals in Amalgam
Ag, Sn, Cu, Zinc, Indium, Palladium
What are the two types of particles used in Amalgam?
lathe cut: irregular filings from cutting ingot of alloy
spherical: round particles by atomising liquid alloy into stream of gas
What is the difference between the original and modern formula?
Modern: superior physical properties due to absence of tin or mercury (gamma 2) = reduced corrosion and creep
How does the alloy type influence Hg required?
Spherical alloy - less Hg (Valiant, Logic Plus)
admixed alloy - more Hg (Valiant PHD, Kermite)
What is the benefit of a high copper amalgam?
less tin/mercury reaction:
increase strength
reduce tarnish and corrosion
reduce creep
Is Gamma 2 good or bad? Why?
Sn8Hg
BAD
corrodes fast, weaker
low copper alloy: Hg reacts more with gamma
Is Gamma 1 good or bad? Why?
Ag2Hg3
GOOD
reduces creep
prevents gamma 2 formation through epsilon in form of eta (epsilon develops crystals on surface of gamma particle)
Dimensional change
High Cu amalgams undergo net contraction
leaves marginal gap
Strength
Develops slowly
spherical alloys strengthen faster (less Hg required)
Corrosion
Tarnishing, corrosion fatigue, galvanic corrosion
crevice corrosion: formation of products containing tin & copper that seals the margin between amalgam and cavity wall
Creep
Mainly due to Gamma 2 influence
high Cu amalgam: more creep resistant
Rigidity
stronger modules of elasticity
What is the alloy to mercury ratio for lathe cut alloys ?
1:1
(excess Hg = loss physical prop.)
What is trituration?
Mixing: Amalgamation.
Combining alloy particles with Hg
What happens after over-trituration?
sets prematurely: weakened rest.
generate heat: creates excess matrix, prevents adequate condensation and adaptation to wall prep.
What happens after under-trituration?
amalgam softer for longer: lower strength
appears shiny: no time for Hg to coat all alloy particles (low strength)
What is the best way to condense amalgam?
Overfill 1mm to reduce Hg brought to surface in rest. then carve later.
Advantages of amalgam
strong and rigid
longevity
cost effective
large rest.
Disadvantages of amalgam
needs mechanical retention
susceptible to corrosion
marginal leakage
Hg content
poor aesthetics
When shouldn't amalgam be used?
prenant women
kidney disease
primary dentition
(must be capsulated)
How is amalgam disposed?
Store in air tight container and seal well (under water)
Send to recycler when full.
What are the main reasons for failure?
1. secondary caries
2. fracture
What factors affect the success of an amalgam restoration?
material handling
oral hygiene, diet, fluoride
selecting high Cu amalgam
Why does tarnishing occur?
Formation of silver and copper sulphides by reactions with sulphur in food and drink
What is the main fracture-type? What are the main causes for this fracture?
Fracture of restoration margins.
Occlusal overload, creep, metal fatigue
How are shallow fissures created when carving amalgam in a Class II restoration?
Half hollenback to sweep.
What happens if the amalgam is carved too early?
Too much removed - over contoured
Keep fissures shallow
What happens if amalgam is carved too late?
Anatomy inaccurate, difficult to carve, under contoured.
(carve when there is a slight resistance)
What must you do once the amalgam is set?
wipe with damp cotton pellet, check occlusion
What are the 3 types of overhang?
I. light catch with explorer: remove w/ hand instrum.
II. moderate definitive overhang: ultrasonic or HI
III. gross overhand: replace
Patient record entry for Class II Amalgam restoration.
6/12/13 TOP, 35MO, caries free, dentine conditioner, lined with Fuji bond LC, amalgam (logic) with LA and rubber dam isolation, occlusion checked, POIG.