Gypsum

Question 1

model

Answer 1

a + likeness of an object

Question 2

How gypsum is made

Answer 2

calcination-process of heating a solid will drive off volatile chemically combined components (i.e. water)

Question 3

varying amts of heat

Answer 3

different products

Question 4

Dihydrate

Answer 4

starting product2CaSo4.2H20

Question 5

Beta Hemihydrate

Answer 5

plaster, irregular shape, spongy, more water

Question 6

Alpha Hemihydrates

Answer 6

regular shape, dense, less water than beta

Question 7

die stone

Answer 7

modified alpha hemihydrate, shorter and thicker crystals, less water than stone for mixing, higher strength than stone

Question 8

mixing time mechanical

Answer 8

20-30 s

Question 9

hand mix time

Answer 9

1 min

Question 10

setting time, how to know intitial set

Answer 10

when the light-Gilmore needle can barely penetrate mixture

Question 11

final setting determiner

Answer 11

barely a mark left by heavy gilmore needle

Question 12

increase water/powder ratio

Answer 12

increased setting time, decreased strength, decreased setting expansion

Question 13

longer vigorous mix means

Answer 13

shorter setting time

Question 14

warm water

Answer 14

shorter setting time-erratic

Question 15

chemical accelerants

Answer 15

Potassion S, NaCL, NaS, Borax

Question 16

Borax

Answer 16

chemical accelerant which accelerates at low c and retards at high c

Question 17

slurry water

Answer 17

provides additonal seeds of nucleation

Question 18

setting expansion mech

Answer 18

crystal of dihydrate is an outgrowth, can intermesh and obstruct growth of adj crystals, excess water during drying –> porous

Question 19

excess water loss during drying

Answer 19

porous structure

Question 20

hydroscopic setting expansion

Answer 20

expansion that occurs when gypsum sets while immersed in water, 2x normal expansion, crystals grow more freely

Question 21

wet strength

Answer 21

=green strength, less

Question 22

dry strength

Answer 22

st. when all excess water is used, 2-3 times of wet st.

Question 23

increase W/P ration

Answer 23

decrease st. (strength)-fewer hydrate crystals per unit V

Question 24

spatulation

Answer 24

increaed mixing time increases st.

Question 25

overmixing

Answer 25

dec st.-dec crystal interlocking

Question 26

inc mixing time

Answer 26

inc. st.

Question 27

type I gypsum

Answer 27

impression plaster, impressions and occlusal records-OBSOLETE-Runny

Question 28

Type II

Answer 28

Model plaster, study models, denture flasking, not used much

Question 29

Type III

Answer 29

dental stone, working casts and mounting on articulators

Question 30

IV

Answer 30

High st. dental stone and low expansion-for wax patterns-used often

Question 31

V

Answer 31

High st high expansion dental stone-dies for cast restirations w/ high casting shrinkage

Question 32

Mounting Stone

Answer 32

faster setting, low expansion, lower strength, altered type III

Question 33

Manipulation of Gypsum

Answer 33

storage, mL water, and stone powder in weight (grams)

Question 34

mixing by hand

Answer 34

parabolic bowl, stiff spatula, water into bowl, powder sifter onto water, mix 1 min (longer mix dec working time), reduce air entrapment (bubbles) by high frequency/low amplitude vibration

Question 35

longer mixing time for gypsum

Answer 35

dec working time

Question 36

mechanical mix

Answer 36

mix water and powder, stir, mix in vacuum, vibrate, attach hose and mix, take of lid, vibrate with lid just barely on, RINSE LID!! Vibrate on smaller machine while you put in each tooth slowly

Question 37

mechanical mix/pouring of an impression

Answer 37

mix water and powder, stir, mix in vacuum, vibrate, attach hose and mix, take of lid, vibrate with lid just barely on, RINSE LID!! Vibrate on smaller machine while you put in each tooth slowly, clean bowl out in garbage and sink

Question 38

T/F can use normal infetion control on cast?

Answer 38

True

Question 39

store above 130?

Answer 39

no

Question 40

gypsum composoition

Answer 40

Calcium sulfate dihydrate

Question 41

Add hardness to home water

Answer 41

gypsum

Question 42

Gypsum product uses in dentistry

Answer 42

diagnostic/models, working models, dies, mounting casts, denture processing, metal casting

Question 43

impression

Answer 43

a negative replica of the oral cavity

Question 44

a negative replica of the oral cavity

Answer 44

impression

Question 45

a positive likeness of an object

Answer 45

model

Question 46

Diagnostic study casts are useful for

Answer 46

Evaluating dentition Treatment planning Patient education Tracking Progress of otho/pros

Question 47

a reproduction of a prepared tooth made from gypsum, metal, or refractory material

Answer 47

die

Question 48

110 to 130 degrees calcination product

Answer 48

Plasters and stone (calcium sulfate hemihydrate)

Question 49

130 to 200 degrees C calcination product

Answer 49

hexagonal anhydrite

Question 50

200 to 1000 degrees calcination product

Answer 50

orthothrombic anhydrite