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Aqueous Impressions

  1. True/False: aqueous impressions are used to make accurate replica or mold of hard and soft oral tissues and can be used for single tooth to whole dentition, or edentulous mouth
    True
  2. what are the two types of aqueous hydrocolloids?
    • agar (reversible)
    • alginate (irreversible)
  3. what are the two twos of impression materials
    • elastomeric impressions
    • aqueous hydrocolloids
  4. what is the indication for agar hydrocolloids
    crown and bridge

    due to its high accuracy
  5. 5 things that make up agar hydrocolloids
    • agar: complex polysaccharide--seaweed: gelling agent 
    • borax: strengthening agent
    • potassium sulfate--improves gypsum surface; overcomes the retarding effect of borax on gypsum cast material 
    • coloring agent
    • water: 85%
  6. 5 factors affecting agar hydrocolloids gelation time
    • sol temp (liquefaction): 70-100*C
    • cooling (gelation) temp: 37-50*C
    • agar content
    • thickness
    • surface area
  7. T/F: alginate hydrocolloids change from the sol phase to the gel phase with a chemical reaction that is reversible
    FALSE, the reaction is irreversible
  8. what is the main ingredient in alginate hydrocolloids
    alginic acid
  9. what is sodium phosphates role in the chemistry of alginate
    it acts as a retarder to slow the reaction
  10. in the alginate reaction: calcium ions from the calcium sulfate dehydrate react preferentially with ______ ___  to form insoluble compound___ ____
    phosphate ions

    calcium phosphate
  11. After the phosphate ions are depleted, the calcium ions react with the _____ ____    -->insoluble calcium alginate, which together with water forms the irreversible calcium alginate gel
    soluble alginate
  12. what does potassium alginate act as in the alginate reaction
    soluble alginate
  13. what does diatomaceous earth or silicate act as in the alginate reaction
    filler
  14. what does calcium sulfate-dihydrate act as in the alginate reaction
    reactor
  15. what does potassium sulfate act as in the alginate reaction
    counter acts the inhibiting effect of the hydrocolloid on the fluoride, silicates or borates setting of gypsum, giving a high-quality surface to the dye
  16. T/F it is acceptable to use alginate hydrocolloids for fixed prosth but not agar hydrocolloids
    FALSE

    agar is acceptable but not alginate
  17. Mixing times of :

    regular alginate:
    fast set:
    • 1 minute
    • 45 seconds
  18. Average working times for materials:

    fast-set materials
    regular-set materials
    Fast-set materials: 1.25-2min

    Regular-set: 3 min up to 4.5min
  19. four factor that affect speed of reaction for setting time
    • power/water ratio
    • temperature
    • mixing rate
    • additives (retarder)
  20. Setting time is temperature dependent

    Colder water-->____ setting time and ____ working time

    Hot water-->____ setting time and ____ working time

    Every ~__* is about ___ ____
    • slower; more
    • quicker; less

    10*; 1 minute
  21. T/F: when you are trying to alter the setting time you should alter the water to powder ratio
    FALSE

    changing this ratio will reduce the strength and accuracy
  22. a function of percent compression, time under compression and time after removal of the compressive load
    permanent deformation
  23. typical elastic recovery value
    98.2% (permanent deformation: 1.8%)
  24. Lower permanent deformation (higher elastic recovery) when (3):
    • percent compression is lower
    • time under compression is shorter
    • recovery time is longer (up to 8 minutes after release of load)
  25. % flexibility of most alginates vs. some hard-set alginates
    Most alginates: 14%

    Some hard-set alginates: 5% to 8%
  26. measuring of force/thickness ratio needed to initiate and continue tearing
    tear strength
  27. Probability of tearing decreases with increased ____ _ _____
    rates of removal
  28. Why shouldn't you leave the stone in the alginate for more than 30-60 minutes?
    the alginate will pull the water from your cast and leave it chalky
  29. three things that disinfect the impressions that are recommended by the CDC
    • household bleach (1/10 dilution) 
    • iodophors
    • synthetic phenols
  30. the best sized tray is ideally ____ mm from tissues to tray
    3-6 mm
  31. when mixing powder and water which should be added to which
    • add the denser one first
    • so add the powder TO water
Author
arikell
ID
338432
Card Set
Aqueous Impressions
Description
Midterm Material 2/14
Updated

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