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Dental Materials > Impression materials > Flashcards

Impression materials Flashcards

1
Q

What is the purpose of using impression materials and gypsum materials?

A

fabricate diagnostic cast

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2
Q

What is the purpose of impression materials?

A

makes NEGATIVE mold of dental structures

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3
Q

What is the synonymous term for irreversible hydrocolloid?

A

alginate for impression

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4
Q

What are the characteristics of ideal impression materials?

A

low cost, long self life, bio-compatible, stable, good handling, pleasant to patient

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5
Q

What are two rigid impression materials?

A

zinc oxide eugenol and plaster

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6
Q

What are two plastic impression materials?

A

wax and compound

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7
Q

What are two elastic impression materials?

A

hydrocolloids and elastomers

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8
Q

What are the limitations of alginate?

A

not used for crown or bridge impression because of the lack of accuracy

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9
Q

define sol

A

resembles a solution but is made of colloidal particles dispersed in liquid

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10
Q

What is the product of alginic acid in water?

A

sol

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11
Q

How can sol transform into gel?

A

through control of temperature and chemical

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12
Q

Define gel

A

entangles network of solid colloidal particles in which liquid is trapped in the interstices and held by capillary forces

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13
Q

When transforming from sol to gel, which control is reversible

A

temperature is reversible

chemically is irreversible

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14
Q

What is the purpose of a reactant in impression material?

A

allows for cross linking

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15
Q

What is the purpose of a retarder in impression material?

A

it controls the reaction

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16
Q

What is the purpose of a reinforced filler in impression material?

A

adds body and strength

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17
Q

What is the purpose of potassium sulfate or alkani zinc fluorides in impression material?

A

provides good surfaces on gypsum dies

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18
Q

What is the affect of increasing the powder and decreasing the water in alginate?

A

Lowering the W/P ratio causes an increase in strength, increase tear resistance, decreases working/setting time

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19
Q

How does lowering the temperature affect alignate?

A

increasing working/setting time

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20
Q

What is mixing time a measure of?

A

how long it takes to form uniform blend

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21
Q

What is working time a measure of?

A

how long from the beginning of the reaction until the setting begins

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22
Q

What is setting time a measure of?

A

how long from the beginning of the mix until the setting reaction is over

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23
Q

Is syneresis the gain or loss of eater to the surrounding?

A

loss

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24
Q

Is imbibition the gain or loss of water into the surrounding?

A

gain

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25
Q

What are the advantages of alginate?

A

economical, easy to use, quick setting, quick setting, fair tasting, hydrophilic, displace saliva/blood, stick trays

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26
Q

What are the disadvantages of alginate?

A

limited detail reproduction, low tear resistance, single pour only, quick pouring required, low dimensional stability

27
Q

What are three well known hydrophobic impression materials?

A

polysulfides
polysiloxanes
polyethers

28
Q

Doe hydrophobic materials have a high or low contact angle?

A

high angle because the water beads up

29
Q

How are polysiloxanes made less hydrophobic?

A

use of a surfactant or incoperating moieties into the silicone backbone

30
Q

How is polysiloxanes controled?

A

by molecular weight of the oligomers

31
Q

What is the major advantage and disadvantage of hydrophobic impression materials?

A 
advantage = dimensionally stable
disadvantage = bubbles because of body fluids
32
Q

Can polysiloxane be re-poured?

A

yes

33
Q

Why should the cast wait to be poured from a polysiloxane

A

all of the hydrogen gas needs to be freed from the mold

34
Q

What are the major disadvantages of polysiloxane?

A

cannot vary setting time, expessive, can produce bubbles in the cast

35
Q

Is polyether more or less hydrophobic than polysiloxane?

A

less hydrophobic = better w/ water

36
Q

What is the disadvantages of polyether?

A

extreemely stiff, low shear strength, bad taste, can cause contact dermatitis

37
Q

Are the different types of gypsum chemically different?

A

No, only the crystal structure is different

38
Q

What form (1-5) of gypsum is most commonly used?

A

type 3

39
Q

What is gypsum composed of?

A

calcium sulfate and two molecules of water

40
Q

What is the process of the removal of water to form the hemihydrate?

A

calcination

41
Q

Is the gypsum reaction reversible ?

A

Yes

42
Q

What does the reverse reaction entail?

A

it is exothermic

When the solid is mixed with water, it refers back to a dihydrate (powder)

43
Q

Can the physical properties of gypsum be manipulated?

A

yes, through the solubility and growth of dihydrate crystals

44
Q

What is the difference between type 1 and 2 dental plaster?

A

type one is the mounting stone while type two is the laboratory plaster used as 2nd pour

45
Q

Why is dental plaster weaker than dental stones?

A

contained pores, thus needs more water for mixing, and the irregular shapes of particles prevents uniform fitting

46
Q

What form (alpha or beta) is the hemihydrate form of gypsum?

A

alpha

47
Q

Why is dental stone used for making casts and molds?

A

high crushing strength and abrasion resistance

48
Q

How is the strength of plaster, stone, and high-strength stone differ?

A

based on shape and form of the hemihydrate crystals

49
Q

What is the characteristics do dental stone and high-strength dental stone crystals possess?

A

more dense and regular in shape

50
Q

What is the greatest disadvantage of gypsum products?

A

poor resistance to abrasion

51
Q

What are some gypsum hardeners?

A

colloidal silica or synthetic resin

52
Q

Are manipulation and setting times directly or indirectly related to the W/P ratio?

A

directly

53
Q

Are strength and setting time directly or indirectly proportional to W/P ratio?

A

indirectly

54
Q

How is the higher setting expansion in dental stone masked?

A

by the additives used in the fomulation

55
Q

What is characteristic of TRIAD?

A

custom tray material, visible light cured, no mixing, and no methyl methacrylate monomers

56
Q

What is the use of dimethacrylate in TRIAD?

A

acts as a softener but after curing allows for a stronger cross linked material

57
Q

What is characteristic of trim and jet materials?

A

provisional, similar chemistry to TRIAD, COLD cured (via mixing)

58
Q

Why is trim and jet used in temporaries rather than composite?

A

much simpler, cheaper, and can be easily manipulated

59
Q

Does an ethyl group add or decreased rigidity?

A

decrease,

and more ductile

60
Q

What is characteristic of mouthguard materials

A

can absorb high impact, high toughness, low rigidity, thermoplastic

61
Q

What is a thermoplastic material?

A

pliable at certain temperatures

62
Q

What is characteristic of a thermoplastic polymer>

A

low softening point, processed in hot water

63
Q

What does a vacuum formed thermoplastic polymer require?

A

die

Dental Materials (6 decks)

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