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88 Cards in this Set
- Front
- Back
What is the primary purpose of taking a dental impression?
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To make a negative reproduction of the dental arches.
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What tissues are included when making an impression?
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Existing teeth,
Restorations, Hard & soft tissues (rugee, tori, Mx tubersity etc.) |
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A diagnostic cast or "study model" forms a ________
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Positive replica of teeth and tissues.
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What material is a diagnostic cast made from?
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Plaster Stone.
(We don't make these at CCD, they're done in a lab or by a dental assistant.) |
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A ________ model is what we work with and will be ground down in the lab.
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Working
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What is the purpose of a Dental Die?
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The lab can cut away the un-necessary elements and only work on those specific area. Like making a partial.
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A dental die is _________ than a study model/diagnostic cast.
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Softer
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What colors does a dental die usually come in?
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Yellow, blue or pink
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What state should impression material be so that it can adapt to teeth and tissues?
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A moldable or plastic state.
**The material then sets into a semi-solid or plastic state.** |
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What are 6 important characteristics of impression material?
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1) Fluid enough to flow into or around area
2) Must harden once in the mouth 3) Must be biocompatible (won't harm tissues) 4) Dimensionally stable (won't expand/contract or change) 5) Easy to handle. 6) Able to disinfect. |
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What is the purpose of impression trays?
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To carry impression materials to the mouth.
*Need to be able to invert, don't want' liquid goo* |
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What are 2 other important aspects of impression trays?
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1) Support the material once its placed into the mouth
2) They need to be rigid enough to prevent distortion. |
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What important feature must be part of either stock trays or custom-made trays?
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They need to be large enough to fit all of the oral structures.
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What is the purpose of the holes (perforations) in the impression trays?
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To create retention..the material locks into the tray because of the holes.
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When taking an impression for a partial, what do you take an impression of?
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Only the area that you need.
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Are metal impression trays perforated?
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Some are and some are not.
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If the metal trays aren't perforated, what needs to be done?
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You need to prime the tray with an adhesive.
It creates a sticky surface the material will adhere to rather than sticking to the teeth. |
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What is a rim-lock in a metal impression tray?
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A raised or rolled edge that the material gets caught underneath and gets locked into the tray.
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What is the main difference between plastic & metal trays after the impression has been taken?
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Plastic are disposable.
Metal must be autoclaved but have to be prep'ed ahead of time (They go in special cleaners to remove the residual material etc.) |
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How do impression tray's come?
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Full uppers/lowers, Half right/left, Anterior only.
They don't have to be for the entire arch. Take the impression on what you need! |
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Hydrocolloids
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A water based colloid that functions as elastic impression materials. (These are used in dentistry.)
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What are the 2 types of hydrocolloids?
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1) Reversible--Agar
2) Irreversible--Alginaties |
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Which of these types of hydrocolloids do we NOT work with at CCD?
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Reversible
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What is the mechanism of actin on a reversible hydrocolloid?
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Water.
Warm water softens, Cool water hardens **They are extremely accurate** |
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The product used in a reversible hydrocolloid is called______-_______.
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agar-agar.
*Its from a seaweed extract.** |
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What types of impression trays are used with a reversible hydrocolloid?
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Stock metal trays.
(The water tubing that goes through them allows for heating/cooling.) |
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Irreversible hydrocolloid is also known as what?
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Alginate *It’s the most commonly used material.*
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What are 4 fabulous traits of alginate?
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1) Its inexpensive
2) Easy to use 3) requires no special equipment 4) numerous uses |
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What are some uses of alginate that we'll work with as Dental Hygienists?
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Mouth guards
Custom fluoride trays Diagnostic models, Bleaching trays, Partial denture frameworks, Fabricate temporary restoratons |
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What is the chemical composition of alginate?
(What ingredients at what %) MUST KNOW THIS! |
55% Diatomaceous earth (ground stone)
15-20% Potassium / sodium alginate (derived from seaweed) 14-20% Calcium sulfate dihydrate 10% Potassium Sulfate 2% trisodium phosphate |
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What is the working time for regular-set alginates?
Fast set alginates? |
2-3 minutes (This is what we work with)
1.5-2 minutes |
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When does working time begin?
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When the powder material and liquid combine.
*The longer one takes to mix the material, the less time one has to load and seat the tray.* |
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What needs to be done to remove the impression from the mouth?
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Need to break the seal!
Use a rapid snap movement to decrease deforming or tearing. |
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Once you remove the impression from the mouth what do you need to do?
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Keep it wet until (wrap in wet paper towel/keep in zip lock baggie) ready to pour up the impression in dental stone (gypsum)
**If its not kept moist the impression will shrink and it won't be accurate.** |
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Before placing in a paper towel/zip lock baggie, what needs to be done to the impression?
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Rinse 1st (to remove any "lunch" debris, then disinfect (cavicide) it immediately!
(3 minute disinfection period) |
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Ideally, when do you want to pour the impression to prevent distortion?
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1 hour of taking the impression
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Alginate that is mixed with too much water will be________.
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Weaker…more likely to tear and it will take longer to set!
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Removing the tray too slowly after the impression may cause the material to ________.
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Tear! Snap it out quickly.
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What are the 6 steps to the impression taking process?
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1) Select the proper tray size (might use different sizes on Mx vs Mn)
2) prepare the necessary materials. 3) Advise patient/patient comfort 4) consider work time/set time 3:00 minutes 5) Rinse after removal 6) Apply disinfectant |
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If you select a tray that is not the correct size for the Pt, what do you do with the tray?
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Rinse, cavicide and place in zip lock bag…we'll recycle it.
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What can be done to a tray to make it wider? What if the tray needs to be extended?
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Heat it up
Wax can be added to the rims to extend the tray. |
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What temperature of water is best to mix with the alginate?
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Cool or room temperature.
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What should I do with the can of alginate before opening and getting started?
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Tumble the can first!
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How much water gets mixed with each level scoop of powder?
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One scoop of water per water line.
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What must be work to avoid inhalation of powder?
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Masks!
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What color does our alginate begin as and what does it change to?
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Begins as purple, changes to pink and once its set its white.
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How do you remove air bubbles from the mix?
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Press it to the side of the bowl.
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Is manual mixing or mechanical mixing better?
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Mechanical, but we don't do this at CCD.
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How do you load the impression tray?
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Load from posterior and work to the anterior. Add large increments as quickly as possible. Smooth the surface with wet fingers and remove excess material.
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Which tray should you "seat" first and why?
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Lower tray first so as to avoid the gag reflex.
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When loading the lower tray, where should I be standing?
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In front of Pt. Apply equal pressure downward.
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When loading the upper tray, where should I be standing?
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Behind the Pt (at 11 or 1)
Seat the anterior of the tray 1st and then the posterior. |
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What should I have the Pt do after loading the upper tray?
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Have Pt tilt head forward and provide them with paper towel.
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What is the regular set time vs fast set time?
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Regular: 2-5 minutes (once in the mouth) Fast set: 1-2 minutes (once in the mouth)
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What is considered an acceptable impression?
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All teeth and alveolar process is recorded
Good detail (including frenum) No debris or distortion Palatal vault is recorded Retro-molar area/tuberosity is recorded |
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Are dental impressions considered contaminated?
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YES! Remove, Rinse and disinfect.
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How long should the impression sit in a bag prior to pouring?
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3-30 minutes
(since placing cavicide on it, don't let it go past 30 mins) |
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What is the purpose of the silicone bite impression?
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To "register" how the Pt's bite comes together.
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Gupsum is a material that is widly found…..
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in nature (They are mined and ground into a powder.)
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What 2 types of gypsym are we concerned with?
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Dihydrate & Hemihydrate
(The difference is in how much they are ground) |
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If you're pouring a diagnostic model you should use _______.
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plaster (white) Very Porous
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If you're making a crown or bridge you use….
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Die stone (it can be cut apart)
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When hemihydrate is mixed with water it becomes a ___________ mixture.
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flowable
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When the impression is mixed with water, what type of reaction occurs in the bowl?
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Endothermic (Creates heat) *Double check this*
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What type of reaction happens when the material hardens? What is the material called?
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Exothermic..heat is give off and causes material to harden.
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When hemihydrate is heated in open vats to 115 C, what happens to the material?
What is the material called? |
It ends up very pourous and somewhat irrregular in its posered shape.
Plaster of B-hemihydrate (Beta-hemihydrate) Its white. |
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If the hemihydrate is heated up under pressurized conditions at a temp > 115C what is the result of the powder particles?
What is the material called? What color is it? |
They are more uniform in shape, less pourous.
Dental Stone or Hemihydrate Yellow |
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If the temperature and pressure are further increased what is the material called?
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Die stone
It makes a more defined type model. |
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What are 2 factors contribute to the strength & (abraision resistance) hardness of the model?
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Shape of the particles and porosity
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The strength of the gypsum products is related to the amount of _______ used to produce the study or working model.
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Water
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What does the difference in type of gypsom depend on?
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The size and shape of the particles,
The porosity of the powder, & they way the powder was processed. |
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Physically, gypsum products are manufactured as? (3 items)
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Plaster, stone (yellow), and high-strength stone
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Larger, irregular particles make the product……?
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more porous and weaker. (Break & abrade easily)
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Smaller, more uniform particles make the product….?
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less porous and stronger
(Don't break as easily or abrade) |
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___________ _________ happens with all gypsum products.
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Setting expansion
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Which product has the highest rate of expansion?
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plaster (white) Very Porous
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Which product has t he lowest rate of expansion?
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Die stone
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Set gypsum stone is not highly ________ in water?
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soluble
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Solubility is directly related to the ___________ of the material.
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porosity.
As such plaster is more more soluble than stone. |
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Exposing models to ________ for a prolonged period of time should be avoided.
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water
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The mix that is created to take impressions should have sufficient _______ to reproduce details of the impression.
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Flow!
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Having too much water will make the mix _________
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weak (less accurate…needs to be like frosting.)
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Having too little water will make the mix _____ ______.
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not flow
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What is the mechanical device we can utilize to assist in mixing? What does it do?
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A Vibrator Gets rid of air bubbles
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When working with yellow lab stone, how do you want to add the water to the powder?
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Gradually.
Its easy to put in too much water and then you have to keep adding more stone |
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What is the approximate working time of lab stone?
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About 5 minutes
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Diagnostic & working casts have two parts.
What are they? |
1) Anatomical portion (replicates the hard and soft structures)
2) The base or "Art Portion" |
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What is the difference between a single pour and a double pour?
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A single pour fills the impression only (no base).
A double pour inverts the impressionon top of a "stone base" |