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