Impression materials

Question 1

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

Answer 1

fabricate diagnostic cast

Question 2

What is the purpose of impression materials?

Answer 2

makes NEGATIVE mold of dental structures

Question 3

What is the synonymous term for irreversible hydrocolloid?

Answer 3

alginate for impression

Question 4

What are the characteristics of ideal impression materials?

Answer 4

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

Question 5

What are two rigid impression materials?

Answer 5

zinc oxide eugenol and plaster

Question 6

What are two plastic impression materials?

Answer 6

wax and compound

Question 7

What are two elastic impression materials?

Answer 7

hydrocolloids and elastomers

Question 8

What are the limitations of alginate?

Answer 8

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

Question 9

define sol

Answer 9

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

Question 10

What is the product of alginic acid in water?

Answer 10

sol

Question 11

How can sol transform into gel?

Answer 11

through control of temperature and chemical

Question 12

Define gel

Answer 12

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

Question 13

When transforming from sol to gel, which control is reversible

Answer 13

temperature is reversible

chemically is irreversible

Question 14

What is the purpose of a reactant in impression material?

Answer 14

allows for cross linking

Question 15

What is the purpose of a retarder in impression material?

Answer 15

it controls the reaction

Question 16

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

Answer 16

adds body and strength

Question 17

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

Answer 17

provides good surfaces on gypsum dies

Question 18

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

Answer 18

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

Question 19

How does lowering the temperature affect alignate?

Answer 19

increasing working/setting time

Question 20

What is mixing time a measure of?

Answer 20

how long it takes to form uniform blend

Question 21

What is working time a measure of?

Answer 21

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

Question 22

What is setting time a measure of?

Answer 22

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

Question 23

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

Answer 23

loss

Question 24

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

Answer 24

gain

Question 25

What are the advantages of alginate?

Answer 25

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

Question 26

What are the disadvantages of alginate?

Answer 26

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

Question 27

What are three well known hydrophobic impression materials?

Answer 27

polysulfides polysiloxanes polyethers

Question 28

Doe hydrophobic materials have a high or low contact angle?

Answer 28

high angle because the water beads up

Question 29

How are polysiloxanes made less hydrophobic?

Answer 29

use of a surfactant or incoperating moieties into the silicone backbone

Question 30

How is polysiloxanes controled?

Answer 30

by molecular weight of the oligomers

Question 31

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

Answer 31

``` advantage = dimensionally stable disadvantage = bubbles because of body fluids ```

Question 32

Can polysiloxane be re-poured?

Answer 32

yes

Question 33

Why should the cast wait to be poured from a polysiloxane

Answer 33

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

Question 34

What are the major disadvantages of polysiloxane?

Answer 34

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

Question 35

Is polyether more or less hydrophobic than polysiloxane?

Answer 35

less hydrophobic = better w/ water

Question 36

What is the disadvantages of polyether?

Answer 36

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

Question 37

Are the different types of gypsum chemically different?

Answer 37

No, only the crystal structure is different

Question 38

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

Answer 38

type 3

Question 39

What is gypsum composed of?

Answer 39

calcium sulfate and two molecules of water

Question 40

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

Answer 40

calcination

Question 41

Is the gypsum reaction reversible ?

Answer 41

Yes

Question 42

What does the reverse reaction entail?

Answer 42

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

Question 43

Can the physical properties of gypsum be manipulated?

Answer 43

yes, through the solubility and growth of dihydrate crystals

Question 44

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

Answer 44

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

Question 45

Why is dental plaster weaker than dental stones?

Answer 45

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

Question 46

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

Answer 46

alpha

Question 47

Why is dental stone used for making casts and molds?

Answer 47

high crushing strength and abrasion resistance

Question 48

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

Answer 48

based on shape and form of the hemihydrate crystals

Question 49

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

Answer 49

more dense and regular in shape

Question 50

What is the greatest disadvantage of gypsum products?

Answer 50

poor resistance to abrasion

Question 51

What are some gypsum hardeners?

Answer 51

colloidal silica or synthetic resin

Question 52

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

Answer 52

directly

Question 53

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

Answer 53

indirectly

Question 54

How is the higher setting expansion in dental stone masked?

Answer 54

by the additives used in the fomulation

Question 55

What is characteristic of TRIAD?

Answer 55

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

Question 56

What is the use of dimethacrylate in TRIAD?

Answer 56

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

Question 57

What is characteristic of trim and jet materials?

Answer 57

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

Question 58

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

Answer 58

much simpler, cheaper, and can be easily manipulated

Question 59

Does an ethyl group add or decreased rigidity?

Answer 59

decrease, | and more ductile

Question 60

What is characteristic of mouthguard materials

Answer 60

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

Question 61

What is a thermoplastic material?

Answer 61

pliable at certain temperatures

Question 62

What is characteristic of a thermoplastic polymer>

Answer 62

low softening point, processed in hot water

Question 63

What does a vacuum formed thermoplastic polymer require?

Answer 63

die