Exam 2: Gypsum

Question 1

replica of teeth and/or
associated supporting bony tissues of one
jaw, prepared from an impression

Answer 1

cast

Question 2

a model of a single tooth,

prepared from an impression

Answer 2

die

Question 3

properties of gypsum, which is not a critical property?

Answer 3

• mechanical
• detail reproduction
• dimensional accuracy/stability
• compatibility w impression materials
• color contrast
• economical

color contrast not critical

Question 4

gypsum is _____ form of ________ and is found as a _____ in different forms

Answer 4

dihydrate, calcium sulfate, mineral

Question 5

most common mineral for gypsum; what is its color?

Answer 5

selenite, transparent

Question 6

supplied powdered form of gypsum product

Answer 6

calcium hemihydrate/beta-hemihydrate/dental plaster

Question 7

Wet process through autoclaving of gypsum

Answer 7

autoclave hemihydrate/alpha hemihydrate/dental stone

Question 8

Dry process through calcination of gypsum

Answer 8

calcined hemihydrate

Question 9

autoclave hemihydrate/alpha hemihydrate/dental stone appearance

Answer 9

colored appearance

Question 10

calcium hemihydrate/beta-hemihydrate/dental plaster appearance

Answer 10

white

Question 11

in the office/lab, hemihydrate calcium sulfate is mixed with ____ and as a result
crystals of the dihydrate form (gypsum) are reformed.

Answer 11

water

Question 12

ratio for plaster

Answer 12

100g/18.6mL

Question 13

goal for consistency

Answer 13

smooth, workable plaster

Question 14

The setting reaction is not simply the re-incorporation of water in the hemihydrate form to
obtain the dihydrate form. Instead, is a process of ________ and _________

Answer 14

dissolution and recrystalization

Question 15

generalized gypsum setting reaction

Answer 15

1. Ca and sulfate ions ready to
   react with water; form dihydrate crystal nuclei
2. crystals of gypsum thrust/interlock which increases friction; paste becomes unworkable
3. thrust causes volumetric expansion
4. further expansion until most of hemihydrate crystals have dissolved

Question 16

most of the final set product is __________

Answer 16

crystallized gypsum

Question 17

The manufacturing process influences _____________________

Answer 17

size and shape of the supplied hemihydrate crystals

Question 18

calcined beta-hemihydrate is made of _____

Answer 18

irregular crystals

Question 19

Autoclaved alpha-hemihydrate is made of ____

Answer 19

smaller prismatic crystals

Question 20

dental plaster is mixed with (more/less) water than dental stone.

Answer 20

more

Question 21

Set dental plaster is ___________ than dental stone

Answer 21

more brittle and weaker

Question 22

autoclaved hemihydrate types

Answer 22

Type III, IV, V

Question 23

calcined hemihydrate types

Answer 23

Type I, II

Question 24

accelerators of setting time

Answer 24

gypsum, potassium sulfate

Question 25

things that slow setting time

Answer 25

borax, potassium citrate

Question 26

increase setting expansion

Answer 26

calcium acetate

Question 27

decrease setting expansion

Answer 27

potassium sulfate

Question 28

All additives used in gypsum products will _____ the final set gypsum

Answer 28

weaken

Question 29

Set casts and dyes should be _______ for obtaining max. mechanical strength
possible

Answer 29

thoroughly dried

Question 30

If cast is not properly dried, remaining water acts as a _____ in the set structure

Answer 30

plasticizer

Question 31

wet process creates…

Answer 31

dental stone

Question 32

dry process creates…

Answer 32

dental plaster

Question 33

which is more porous, dental plaster or dental stone?

Answer 33

dental plaster