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56 Cards in this Set
- Front
- Back
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What type of force is used in the lost wax technique?
A. Mechanical pushing B. Gravity C. Vibration D. Gas pressure E. Centrifugal |
E. Centrifugal
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What is initially created, which will be replaced by the actual casing material?
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A wax model
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What type of material is used to take the place of the void left by the burned out wax?
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metal
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Some crowns combine metal and ceramics into one. What is the benefit of the metal? The ceramic (porcelain)?
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Metal - strength and accuracy
Ceramic - esthetics |
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Put these steps in order
A. Master die prep B. Burnout C. Casting D. Wax pattern formation E. Cavity/tooth prep F. Impression of prep G. Investment of pattern H. Finish and delivery |
E, F, A, D, G, B, C, H
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True or False, each type of restorative material requires a different amount of tooth removal prior to taking a mold
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True. Some materials need to be thicker/thinner than others
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Which of the following needs to be the thickest for structural integrity?
All metal Metal-ceramic All ceramic |
All ceramic. It is brittle and will fracture easily in thin layers. This means ceramic needs more 'reduction' of tooth structure, as in more tooth must be removed
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What is the max expansion for type IV die stone? Type V?
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.1%, .3%
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What is the main disadvantage of type IV die stone?
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It has poor abrasion resistance
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You can add silver plating, cyanoacrylate coating, and die hardeners to type IV die stone to make it stronger. What 2 quality actually gets worse when you do this?
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increases die dimensions
reduces casting accuracy |
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Why does the die material need to expand?
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Because the alloy shrinks (contracts)
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Which of these expands?
Die material Casting alloy Investment material |
Die material
Investment material |
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What is the name of material that can be used as both a die stone and investment material based on what water you add?
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Divestment (made by Whip Mix Corp.)
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Name 4 die materials
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electroformed dies (Cu- or Ag-plating)
Amalgam Epoxy, acrylic or polyester resins Resin-reinforced gypsum |
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A die spacer should end __mm from the internal line angles
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0.5mm
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What material provides the relief space for cement?
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die spacer
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What forms the channel for the casting alloy to flow into the invested ring after the wax pattern has been burned out?
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sprue former
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When restoring a single tooth, you attach a sprue to it known as a direct sprue. What if you're doing a bridge with several teeth?
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Use an indirect sprue
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Large restorations use a sprue made from ___ where small restorations use a sprue made from ___
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wax, resin
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The sprue thickness should be about the same size as the (thickest/thinnest) part of the wax pattern
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thickest
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What happens if the sprue is not thick enough?
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You get suck-back porosity
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What is used to overcome suck-back porosity
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use a reservoir
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Attach sprue former to the (largest/smallest) cross-sectional area on pattern so that molten alloy flows to the margins and minimizes the risk for turbulence during flow
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largest
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Sprue former length should place pattern about __mm from open end of ring
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6
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What does burnout depend on?
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The composition of sprue former
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If the investment is too thin (less than 6mm of space), what might happen?
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it might break
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The sprue base is also known as what?
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crucible former
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You are in lab and choose a casting ring that is level with the edge of the wax pattern. Why will this not work?
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You need an extra 6mm of space ABOVE the restoration so that when you burn it out, you have 6mm of investment above the void
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The goal of the casting ring liners is to permit (expansion/contraction) of investment material in the casting ring
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expansion
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What are the two main types of casting ring liners available?
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aluminum silicate ceramic liner
Cellulose (paper) liner |
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True or False, the ring liner may overlap so long as it is less than 5 mm thick
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False, DON'T overlap ever!!
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True or False, the ring liners must be used wet
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False, can be used wet or dry
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Ring liners should be at least __ mm thick
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1 mm
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True or False, you may have two ring liners used at once
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True (just don't overlap a single one! It needs to be even all the way around)
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Do you get greater expansion with a wet or dry ring liner?
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wet
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(hygroscopic/thermal) expansion exhibits a greater percentage of expansion
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hygroscopic
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You should mix the investment (manually/mechanically) in (open air/vacuum)
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mechanically, vacuum
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A pattern cleaner is used to (reduce/increase) surface tension of wax and improve wetting by investment
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reduce
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Which of these is considered "low heat"?
hygroscopic expansion thermal expansion |
hygroscopic
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When you invest wax, any air bubbles become what?
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metal nodules
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What is the solidification temperature for type II gold alloys?
MCR alloys? |
927C
1260C |
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What should be the TOTAL contraction for dental alloys?
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1.5 vol%
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The expansion of the investment must __ the contraction of the casting alloy
A. Equal B. Be more than C. Be less than D. Depends on what your goal is |
A. Equal
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If the gypsum-bonded investment is heated over 700C, what can occur?
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alligator skin appearance on alloy
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The margins of the casting should freeze (first/last) while the button should freeze (first/last)
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first, last
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Why should the margins freeze first?
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So that the remaining molten metal can compensate for the shrinkage that occurs when the casting shrinks
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At what temperature (in C) does the alloy glow?
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1000C
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The excess alloy after casting is known as what?
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a botton
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You should pickle the casting in a(n) (acid/base)
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acid
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Which comes first, sand-blasting or pickling?
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sand-blasting
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Should you cut off the sprue before or after you pickle?
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after
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The opening of the margins are typically how big? (in micrometers)
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a bit > than 25 micrometers
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How wide is a human hair? (in micrometers)
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40-60 micrometers
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About how wide is an explorer tip? (in micrometers)
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>100 micrometers
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If an explorer catches under a margin, you know it's deficient but if it doesn't cast, that doesn't mean it's perfect. Why?
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The margin should only be about 25 micrometers whereas an explorer is 100 micrometers. If a 100 micrometer tip detects a margin, then the margin is at least 100 micrometers, much too big. However, it would likely not catch a 50 micrometer margin, though 50 would still be too big.
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Most cements are fairly (soluble/insoluble) in the mouth
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soluble
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