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17 Cards in this Set
- Front
- Back
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dental amalgam
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alloy-mixture of two or more metals
alloy in amalgam is mostly silver but contains copper, tin & zinc when silver based allow is mixed with mercury, the reaction is amalgamation lacks esthetics |
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lathe cut alloy particles
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formed by shaving fine particles off an ingot of the alloy with the use of a lathe
particles are shifted to separate them into fine & ultra fine particles |
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spherical alloy particles
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produced by spraying molten alloy into an inert gas
formed as the atomized droplets cool |
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admixed particles
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consist of a mixture of lathe-cut & spherical particles
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alloy composition
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considered to be high copper confer (10%-30%)
compared with their predecessors (2% to 4%) silver (40%-70%) tin (12%-30%) mercury (43&-50%) |
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silver in amalgam
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setting expansion
increases strength corrosion resistance |
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tin in amalgam
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setting contraction
decreases strength corrosion resistance |
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copper in amalgam
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setting expansion
increases strength corrosion resistance |
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zinc in amalgam
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reduces oxidation of other metals
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gamma phase
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silver alloy phase
it is the strongest phase and involves the least corrosion |
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gamma-1 phase
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consists of mercury reacting with silver
strong and corrosion resistant |
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gamma 2 phase
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consists of the faction of mercury with tin
weak and corrodes easily |
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tarnish
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oxidation attacks surface of the amalgam & extends slightly below the surface
results from contact with oxygen chlorides, & sulfides in the mouth causes dark dull appearance that is not destructive to amalgam |
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corrosion
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chemical reaction between amalgam & substances in saliva or food that results in oxidation
2 dissimiliar metals interact in a solution that contains electrolytes an electrical current is generated between the metals (galvanism) |
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creep
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gradual change in shape of the restoration resulting from compression by the opposing dentition
associated with gamma 2 phase, seen with low copper alloys & results in deterioration of the margins |
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what is the strongest directly placed restorative materials
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amalgam
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high copper alloys
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mostly admixed or spherical ( needs -10% mercury)
still use matrix band, wedge to establish good proximal contact has higher 1 & 24 hour compressive strengths than admixed 24 hours admixed & spherical high-copper shrinks slightly whereas low copper expands |
