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28 Cards in this Set
- Front
- Back
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What is gypsum |
Crystalized and needs whater a refined powder that is composed of calcium sulfate hemihydrate. When added to water hydration occurs causing the formation of dihydrate which is in turn what becomes an interlocking of crystals/ Hardened stone |
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What is the purpose of Gypsum material |
Positive replications of oral structures |
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Define Study model |
For planning Tx or record tx phases |
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Define Cast? |
Replica on which an appliance is fabricated |
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Describe Die? |
Replica that is a seperated single tooth (ONE PART OF A MODEL) |
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Define articulator? |
Labortory instrument used to mimic movements of the mouth/TMJ |
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What does working time/intital setting time mean? |
From the time of mixing to time of semi solid state |
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What does Final setting time mean? |
Rigid and can safetly be removed from the impression |
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What are the different types of Gypsum (3) |
Plaster Stone High strength stone/ Improved stone |
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Explain Plaster |
Weakest Least expensive Porous, white Beta hemihydrate TYPE II |
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What is plaster used for |
Articulations |
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Explain Stone |
Powder is more regular in shape Stronger than plaster Yellow colored Alpha hemidydrate TYPE III |
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What is stone most used for |
Cast and model dentures and partials |
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Explain high strength stone/ improved stone |
Strongest Dense particles DIE STONE TYPE IV |
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What is High strength stone/ improved stone used for? |
Dies and casts intended for crown and bridge work |
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What are the water powder ratios for Plaster Stone Improved stone |
Plaster: 45-50ml water/ 100g powder Stone: 28-30 ml water/ 100g powder Improved stone: 19-24 ml water/ 100g powder |
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The ratios set for the different types of stone are designed to |
accomade the characteristics or properties that the stone have when mixing with water |
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What can increase the setting time? (4) |
Decrease rate of mixing Higher water/ powder ratio Borax (retarder) chemical Colder water |
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What can decrease the setting time (4) |
Increased mixing Lower water/powder ration Potassiu sulfate (Accelerator) Warm Water |
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EXPANSION WHICH TYPE expans the most |
Plaster |
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What are the percentages of expansion for the three stone |
Plaster: 0.2-0.3% Stone: 0.08-0.10% Improved Stone: 0.05-0.07% is the least |
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What is happening during expansion ? |
Crystals that are being formed grow therefore causing an outward thrust. External expansion occurs with internal porosity |
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How can you change expansion |
Less water with increased spatulation= Increased expansion Increased water with decreased spatulation= Descreased expansion |
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What are the two types of mixing |
Hand mixing Vacuum mixing |
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How is hand mixing done |
mix until smooth, and homogenus mix is achieved Wipin motion is used to prevent incorption of air |
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How is vacuum mixing done |
Mechanical mixing More consistency with less air trapped in mixture |
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What is used to assist the flow of gypsum |
Vibrator |
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Surface tension relief can be accomplished by using what |
Designed liquied that can be purchased in a spray bottle |
