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Occlusion > irreversable hydrocolloids and dental gypsum products (complete) > Flashcards

irreversable hydrocolloids and dental gypsum products (complete) Flashcards

1
Q

what is the common name for irreversable hydrocolloids

A

alginate

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2
Q

when is irreversable hydrocolloid used (alginate)

A

diagnostic impressions
facial moulages
removable prosthesis
used in wound healing to form non-adhesive bandages

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3
Q

What does irreversable mean (irreversable hydrocolloids)

A

once the impression is made, it can’t be resoftened and used again (one way gelation)

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4
Q

what do the two parts of hydro-colloid mean

A 
hydro = water
colloid = glue
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5
Q

are there reversable hydrocolloids

A

yes

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6
Q

when are reversable hydrocolloids used

A

impressions of teeth for crowns and bridges

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7
Q

what are the problems with reversable hydrocolloids

A

need special equipment
harder to do
fairly fragile

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8
Q

what are the benefits of reversable hydrocolloids

A

they are accurate

can be heated up, melted, then reused again

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9
Q

where does the agar component of alginate come from

A

giant kelp

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10
Q

what kind of reaction takes the alginate from the sol state to the gel state

A

a chemical reaction

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11
Q

why is alginate so widely used

A

because it is easy to use

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12
Q

what are the two things in alginate, the ratio of which determines the strength and elasticity of the alginate

A

mannuronate

guluronate

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13
Q

what is the alginate like if the ratio of mannuronate to guluronate is high

A

they are weaker and more elastic

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14
Q

what is the alginate like if the ratio guluronate to mannuronate is high

A

they are stronger and more brittle

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15
Q

What is the most abundent material in alginate

A

diatomaceous earth

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16
Q

what is diatomaceous earth

A

fossilized diatoms (hard shelled algae)

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17
Q

what is the purpose of diatomaceous earth

A

a filler material that is used to kill bugs

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18
Q

what are the two main chemical reactors in alginate

A

potassium alginate and calcium sulfate

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19
Q

are gypsum products versitile or not

A

very versatile

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20
Q

what are gypsum products used for in dentistry

A 
making edentulous impressions
making casts from impressions
mounting casts on articulators
investments for casting and soldering
indexes for dental repairs
21
Q

where do gypsum products come from

A

a rock that is formed from the evaporation of sea water, has calcium and sulfate in it. it is mined in open pit mines or quarries

22
Q

what are the steps in getting from calcium sulfate dihydrate to gypsum(hardened calcium sulfate dihydrate)

A
  1. heat up calcium sulfate dihydrate
  2. gives up water and becomes calcium sulfate hemihydrate
  3. mix that with water and the reaction reverses, gives off heat, and hardens into gypsum (hardened calcium sulfate dihydrate)
23
Q

is the reaction of calcium sodium hemihydrate with water that forms gypsum (calcium sodium dihydrate) endo or exothermic

A

exothermic

24
Q

how do you know when your gypsum has sufficiently hardened

A

when the gypsum is no longer warm

25
Q

What are the different types of dental stones

A

Type 2 = plaster (pourous plaster)
Type 3 = low to moderate strength
Type 4 = high strength low expansion
Type 5 = high strength high expansion

26
Q

what are the characteristics of plaster

A

irregular crystal structure
porous
soft
less accurate

27
Q

what are the characteristics of dental stone

A 
regular crystal structure
less porous
harder
greater compressive strength
more accurate
28
Q

what are the important parameters to evaluate gypsum

A
  1. fluidity/viscosity at pouring
  2. setting time
  3. setting expansion
  4. compressive strength
  5. reproduction of detail
  6. surface hardness
  7. abrasion resistance
29
Q

what is the viscosity of gypsum

A

how runny it is,

the lower the viscosity the more runny

30
Q

what is the setting time of gypsum

A

the amount of time it takes the gypsum to harden after mixing

31
Q

why is setting time one of the most important characteristics of gypusm

A

because too short of a setting time doesn’t allow it to get set into the impression, and too long of a setting time means it takes too long

32
Q

what is setting expansion of gypsum

A

the amount of volumetric expansion that occurs as the stone hardens

33
Q

what would happen to a crown made on a stone that has high setting expansion

A

the crown would be too large

34
Q

what is the compressive strength of the stone

A

how resistant to failure the gypsum is to compressive strength

35
Q

compressive strength is highly dependent on what

A

the water to powder ratio (more water = less compressive strength)

36
Q

what is the reproduction of detail of dental stones

A

how detailed of impressions the stone will be

37
Q

which have higher reproduction of detail type 1 and 2 dental stone or type 3,4 and 5 dental stone

A

type 3, 4, and 5 have higher reproduction of detail

38
Q

what is surface hardness and resistance to abraision for gypsum

A

how hard the surface is, and how hard to scratch it it is

39
Q

what things affect the parameters of gypsum products

A 
ratio of powder to water
spatulation
humidity
temperature
additives
pH
40
Q

what does increasing the ratio of water to powder do to gypsum

A
  1. decreases compressive strength
  2. decreases surface hardness and abrasion resistance
  3. increases the porosity of the gypsum
41
Q

what does increased spatulation do to the gypsum

A
  1. accelerates setting time (causes more solidifying nuclei to form)
42
Q

What does humidity do to gypsum

A

humidity below 70% = faster setting time

humidity above 70% = slower setting time

43
Q

what is the easiest way to make sure that humidity doesn’t affect the setting time of your gypsum

A

keep the container sealed

44
Q

what affect does temperature have on gypsum

A

higher temp = shorter setting time

lower temp = longer setting time

45
Q

which is the physical property has the most effect on gypsum

A

temperature

46
Q

what are the two common additives to gypsum

A

potassium sulfate

NaCl

47
Q

what does potassium sulfate do to gypsum

A

accelerates setting time

improves surface quality

48
Q

what does NaCl do to gypsum

A

increases setting expansion

shortens setting time

49
Q

how does pH affect gypsum

A

low pH increases setting time (saliva is low pH)

high pH decreases setting time

Occlusion (7 decks)

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